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Comet

A comet is an icy, small Solar System body that warms and begins to release gases when passing close to the Sun, a process called outgassing. This produces an extended, gravitationally unbound atmosphere or coma surrounding the nucleus, and sometimes a tail of gas and dust gas blown out from the coma. These phenomena are due to the effects of solar radiation and the outstreaming solar wind plasma acting upon the nucleus of the comet. Comet nuclei range from a few hundred meters to tens of kilometers across and are composed of loose collections of ice, dust, and small rocky particles. The coma may be up to 15 times Earth's diameter, while the tail may stretch beyond one astronomical unit. If sufficiently close and bright, a comet may be seen from Earth without the aid of a telescope and can subtend an arc of up to 30° (60 Moons) across the sky. Comets have been observed and recorded since ancient times by many cultures and religions.

Comets usually have highly eccentric elliptical orbits, and they have a wide range of orbital periods, ranging from several years to potentially several millions of years. Short-period comets originate in the Kuiper belt or its associated scattered disc, which lie beyond the orbit of Neptune. Long-period comets are thought to originate in the Oort cloud, a spherical cloud of icy bodies extending from outside the Kuiper belt to halfway to the nearest star. Long-period comets are set in motion towards the Sun by gravitational perturbations from passing stars and the galactic tide. Hyperbolic comets may pass once through the inner Solar System before being flung to interstellar space. The appearance of a comet is called an apparition.

Extinct comets that have passed close to the Sun many times have lost nearly all of their volatile ices and dust and may come to resemble small asteroids. Asteroids are thought to have a different origin from comets, having formed inside the orbit of Jupiter rather than in the outer Solar System. However, the discovery of main-belt comets and active centaur minor planets has blurred the distinction between asteroids and comets. In the early 21st century, the discovery of some minor bodies with long-period comet orbits, but characteristics of inner solar system asteroids, were called Manx comets. They are still classified as comets, such as C/2014 S3 (PANSTARRS). Twenty-seven Manx comets were found from 2013 to 2017.

, there are 4,584 known comets. However, this represents a very small fraction of the total potential comet population, as the reservoir of comet-like bodies in the outer Solar System (in the Oort cloud) is about one trillion. Roughly one comet per year is visible to the naked eye, though many of those are faint and unspectacular. Particularly bright examples are called "great comets". Comets have been visited by uncrewed probes such as NASA's Deep Impact, which blasted a crater on Comet Tempel 1 to study its interior, and the European Space Agency's Rosetta, which became the first to land a robotic spacecraft on a comet.

Etymology
The word comet derives from the Old English cometa from the Latin comēta or comētēs. That, in turn, is a romanization of the Greek κομήτης 'wearing long hair', and the Oxford English Dictionary notes that the term (ἀστὴρ) κομήτης already meant 'long-haired star, comet' in Greek. Κομήτης was derived from κομᾶν 'to wear the hair long', which was itself derived from κόμη  'the hair of the head' and was used to mean 'the tail of a comet'.

The astronomical symbol for comets (represented in Unicode) is, consisting of a small disc with three hairlike extensions.

Nucleus

The solid, core structure of a comet is known as the nucleus. Cometary nuclei are composed of an amalgamation of rock, dust, water ice, and frozen carbon dioxide, carbon monoxide, methane, and ammonia. As such, they are popularly described as "dirty snowballs" after Fred Whipple's model. Comets with a higher dust content have been called "icy dirtballs". The term "icy dirtballs" arose after observation of Comet 9P/Tempel 1 collision with an "impactor" probe sent by NASA Deep Impact mission in July 2005. Research conducted in 2014 suggests that comets are like "deep fried ice cream", in that their surfaces are formed of dense crystalline ice mixed with organic compounds, while the interior ice is colder and less dense.

The surface of the nucleus is generally dry, dusty or rocky, suggesting that the ices are hidden beneath a surface crust several metres thick. The nuclei contains a variety of organic compounds, which may include methanol, hydrogen cyanide, formaldehyde, ethanol, ethane, and perhaps more complex molecules such as long-chain hydrocarbons and amino acids. In 2009, it was confirmed that the amino acid glycine had been found in the comet dust recovered by NASA's Stardust mission. In August 2011, a report, based on NASA studies of meteorites found on Earth, was published suggesting DNA and RNA components (adenine, guanine, and related organic molecules) may have been formed on asteroids and comets.

The outer surfaces of cometary nuclei have a very low albedo, making them among the least reflective objects found in the Solar System. The Giotto space probe found that the nucleus of Halley's Comet (1P/Halley) reflects about four percent of the light that falls on it, and Deep Space 1 discovered that Comet Borrelly's surface reflects less than 3.0%; by comparison, asphalt reflects seven percent. The dark surface material of the nucleus may consist of complex organic compounds. Solar heating drives off lighter volatile compounds, leaving behind larger organic compounds that tend to be very dark, like tar or crude oil. The low reflectivity of cometary surfaces causes them to absorb the heat that drives their outgassing processes.

Comet nuclei with radii of up to 30 km have been observed, but ascertaining their exact size is difficult. The nucleus of 322P/SOHO is probably only 100 - 200 m in diameter. A lack of smaller comets being detected despite the increased sensitivity of instruments has led some to suggest that there is a real lack of comets smaller than 100 m across. Known comets have been estimated to have an average density of 0.6 g/cm3. Because of their low mass, comet nuclei do not become spherical under their own gravity and therefore have irregular shapes.

Roughly six percent of the near-Earth asteroids are thought to be the extinct nuclei of comets that no longer experience outgassing, including 14827 Hypnos and 3552 Don Quixote.

Results from the Rosetta and Philae spacecraft show that the nucleus of 67P/Churyumov–Gerasimenko has no magnetic field, which suggests that magnetism may not have played a role in the early formation of planetesimals. Further, the ALICE spectrograph on Rosetta determined that electrons (within 1 km above the comet nucleus) produced from photoionization of water molecules by solar radiation, and not photons from the Sun as thought earlier, are responsible for the degradation of water and carbon dioxide molecules released from the comet nucleus into its coma. Instruments on the Philae lander found at least sixteen organic compounds at the comet's surface, four of which (acetamide, acetone, methyl isocyanate and propionaldehyde) have been detected for the first time on a comet.

Coma

The streams of dust and gas thus released form a huge and extremely thin atmosphere around the comet called the "coma". The force exerted on the coma by the Sun's radiation pressure and solar wind cause an enormous "tail" to form pointing away from the Sun.

The coma is generally made of water and dust, with water making up to 90% of the volatiles that outflow from the nucleus when the comet is within 3 to 4 astronomical units (450,000,000 to 600,000,000 km; 280,000,000 to 370,000,000 mi) of the Sun. The parent molecule is destroyed primarily through photodissociation and to a much smaller extent photoionization, with the solar wind playing a minor role in the destruction of water compared to photochemistry. Larger dust particles are left along the comet's orbital path whereas smaller particles are pushed away from the Sun into the comet's tail by light pressure.

Although the solid nucleus of comets is generally less than 60 km across, the coma may be thousands or millions of kilometers across, sometimes becoming larger than the Sun. For example, about a month after an outburst in October 2007, comet 17P/Holmes briefly had a tenuous dust atmosphere larger than the Sun. The Great Comet of 1811 had a coma roughly the diameter of the Sun. Even though the coma can become quite large, its size can decrease about the time it crosses the orbit of Mars around 1.5 AU from the Sun. At this distance the solar wind becomes strong enough to blow the gas and dust away from the coma, and in doing so enlarging the tail. Ion tails have been observed to extend one astronomical unit (150 million km) or more.

Both the coma and tail are illuminated by the Sun and may become visible when a comet passes through the inner Solar System, the dust reflects sunlight directly while the gases glow from ionisation. Most comets are too faint to be visible without the aid of a telescope, but a few each decade become bright enough to be visible to the naked eye. Occasionally a comet may experience a huge and sudden outburst of gas and dust, during which the size of the coma greatly increases for a period of time. This happened in 2007 to Comet Holmes.

In 1996, comets were found to emit X-rays. This greatly surprised astronomers because X-ray emission is usually associated with very high-temperature bodies. The X-rays are generated by the interaction between comets and the solar wind: when highly charged solar wind ions fly through a cometary atmosphere, they collide with cometary atoms and molecules, "stealing" one or more electrons from the atom in a process called "charge exchange". This exchange or transfer of an electron to the solar wind ion is followed by its de-excitation into the ground state of the ion by the emission of X-rays and far ultraviolet photons.

Bow shock
Bow shocks form as a result of the interaction between the solar wind and the cometary ionosphere, which is created by the ionization of gases in the coma. As the comet approaches the Sun, increasing outgassing rates cause the coma to expand, and the sunlight ionizes gases in the coma. When the solar wind passes through this ion coma, the bow shock appears.

The first observations were made in the 1980s and 1990s as several spacecraft flew by comets 21P/Giacobini–Zinner, 1P/Halley, and 26P/Grigg–Skjellerup. It was then found that the bow shocks at comets are wider and more gradual than the sharp planetary bow shocks seen at, for example, Earth. These observations were all made near perihelion when the bow shocks already were fully developed.

The Rosetta spacecraft observed the bow shock at comet 67P/Churyumov–Gerasimenko at an early stage of bow shock development when the outgassing increased during the comet's journey toward the Sun. This young bow shock was called the "infant bow shock". The infant bow shock is asymmetric and, relative to the distance to the nucleus, wider than fully developed bow shocks.

Tails
In the outer Solar System, comets remain frozen and inactive and are extremely difficult or impossible to detect from Earth due to their small size. Statistical detections of inactive comet nuclei in the Kuiper belt have been reported from observations by the Hubble Space Telescope but these detections have been questioned. As a comet approaches the inner Solar System, solar radiation causes the volatile materials within the comet to vaporize and stream out of the nucleus, carrying dust away with them.

The streams of dust and gas each form their own distinct tail, pointing in slightly different directions. The tail of dust is left behind in the comet's orbit in such a manner that it often forms a curved tail called the type II or dust tail. At the same time, the ion or type I tail, made of gases, always points directly away from the Sun because this gas is more strongly affected by the solar wind than is dust, following magnetic field lines rather than an orbital trajectory. On occasions—such as when Earth passes through a comet's orbital plane, the antitail, pointing in the opposite direction to the ion and dust tails, may be seen.

The observation of antitails contributed significantly to the discovery of solar wind. The ion tail is formed as a result of the ionization by solar ultra-violet radiation of particles in the coma. Once the particles have been ionized, they attain a net positive electrical charge, which in turn gives rise to an "induced magnetosphere" around the comet. The comet and its induced magnetic field form an obstacle to outward flowing solar wind particles. Because the relative orbital speed of the comet and the solar wind is supersonic, a bow shock is formed upstream of the comet in the flow direction of the solar wind. In this bow shock, large concentrations of cometary ions (called "pick-up ions") congregate and act to "load" the solar magnetic field with plasma, such that the field lines "drape" around the comet forming the ion tail.

If the ion tail loading is sufficient, the magnetic field lines are squeezed together to the point where, at some distance along the ion tail, magnetic reconnection occurs. This leads to a "tail disconnection event". This has been observed on a number of occasions, one notable event being recorded on 20 April 2007, when the ion tail of Encke's Comet was completely severed while the comet passed through a coronal mass ejection. This event was observed by the STEREO space probe.

In 2013, ESA scientists reported that the ionosphere of the planet Venus streams outwards in a manner similar to the ion tail seen streaming from a comet under similar conditions."

Jets
Uneven heating can cause newly generated gases to break out of a weak spot on the surface of comet's nucleus, like a geyser. These streams of gas and dust can cause the nucleus to spin, and even split apart. In 2010 it was revealed dry ice (frozen carbon dioxide) can power jets of material flowing out of a comet nucleus. Infrared imaging of Hartley 2 shows such jets exiting and carrying with it dust grains into the coma.

Orbital characteristics
Most comets are small Solar System bodies with elongated elliptical orbits that take them close to the Sun for a part of their orbit and then out into the further reaches of the Solar System for the remainder. Comets are often classified according to the length of their orbital periods: The longer the period the more elongated the ellipse.

Short period
Periodic comets or short-period comets are generally defined as those having orbital periods of less than 200 years. They usually orbit more-or-less in the ecliptic plane in the same direction as the planets. Their orbits typically take them out to the region of the outer planets (Jupiter and beyond) at aphelion; for example, the aphelion of Halley's Comet is a little beyond the orbit of Neptune. Comets whose aphelia are near a major planet's orbit are called its "family". Such families are thought to arise from the planet capturing formerly long-period comets into shorter orbits.

At the shorter orbital period extreme, Encke's Comet has an orbit that does not reach the orbit of Jupiter, and is known as an Encke-type comet. Short-period comets with orbital periods less than 20 years and low inclinations (up to 30 degrees) to the ecliptic are called traditional Jupiter-family comets (JFCs). Those like Halley, with orbital periods of between 20 and 200 years and inclinations extending from zero to more than 90 degrees, are called Halley-type comets (HTCs). , 70 Encke-type comets, 100 HTCs, and 755 JFCs have been reported.

Recently discovered main-belt comets form a distinct class, orbiting in more circular orbits within the asteroid belt.

Because their elliptical orbits frequently take them close to the giant planets, comets are subject to further gravitational perturbations. Short-period comets have a tendency for their aphelia to coincide with a giant planet's semi-major axis, with the JFCs being the largest group. It is clear that comets coming in from the Oort cloud often have their orbits strongly influenced by the gravity of giant planets as a result of a close encounter. Jupiter is the source of the greatest perturbations, being more than twice as massive as all the other planets combined. These perturbations can deflect long-period comets into shorter orbital periods.

Based on their orbital characteristics, short-period comets are thought to originate from the centaurs and the Kuiper belt/scattered disc —a disk of objects in the trans-Neptunian region—whereas the source of long-period comets is thought to be the far more distant spherical Oort cloud (after the Dutch astronomer Jan Hendrik Oort who hypothesized its existence). Vast swarms of comet-like bodies are thought to orbit the Sun in these distant regions in roughly circular orbits. Occasionally the gravitational influence of the outer planets (in the case of Kuiper belt objects) or nearby stars (in the case of Oort cloud objects) may throw one of these bodies into an elliptical orbit that takes it inwards toward the Sun to form a visible comet. Unlike the return of periodic comets, whose orbits have been established by previous observations, the appearance of new comets by this mechanism is unpredictable. When flung into the orbit of the sun, and being continuously dragged towards it, tons of matter are stripped from the comets which greatly influence their lifetime; the more stripped, the shorter they live and vice versa.

Long period

Long-period comets have highly eccentric orbits and periods ranging from 200 years to thousands or even millions of years. An eccentricity greater than 1 when near perihelion does not necessarily mean that a comet will leave the Solar System. For example, Comet McNaught had a heliocentric osculating eccentricity of 1.000019 near its perihelion passage epoch in January 2007 but is bound to the Sun with roughly a 92,600-year orbit because the eccentricity drops below 1 as it moves farther from the Sun. The future orbit of a long-period comet is properly obtained when the osculating orbit is computed at an epoch after leaving the planetary region and is calculated with respect to the center of mass of the Solar System. By definition long-period comets remain gravitationally bound to the Sun; those comets that are ejected from the Solar System due to close passes by major planets are no longer properly considered as having "periods". The orbits of long-period comets take them far beyond the outer planets at aphelia, and the plane of their orbits need not lie near the ecliptic. Long-period comets such as C/1999 F1 and C/2017 T2 (PANSTARRS) can have aphelion distances of nearly 70000 AU with orbital periods estimated around 6 million years.

Single-apparition or non-periodic comets are similar to long-period comets because they have parabolic or slightly hyperbolic trajectories when near perihelion in the inner Solar System. However, gravitational perturbations from giant planets cause their orbits to change. Single-apparition comets have a hyperbolic or parabolic osculating orbit which allows them to permanently exit the Solar System after a single pass of the Sun. The Sun's Hill sphere has an unstable maximum boundary of 230000 AU. Only a few hundred comets have been seen to reach a hyperbolic orbit (e > 1) when near perihelion that using a heliocentric unperturbed two-body best-fit suggests they may escape the Solar System.

, only two objects have been discovered with an eccentricity significantly greater than one: 1I/ʻOumuamua and 2I/Borisov, indicating an origin outside the Solar System. While ʻOumuamua, with an eccentricity of about 1.2, showed no optical signs of cometary activity during its passage through the inner Solar System in October 2017, changes to its trajectory—which suggests outgassing—indicate that it is probably a comet. On the other hand, 2I/Borisov, with an estimated eccentricity of about 3.36, has been observed to have the coma feature of comets, and is considered the first detected interstellar comet. Comet C/1980 E1 had an orbital period of roughly 7.1 million years before the 1982 perihelion passage, but a 1980 encounter with Jupiter accelerated the comet giving it the largest eccentricity (1.057) of any known solar comet with a reasonable observation arc. Comets not expected to return to the inner Solar System include C/1980 E1, C/2000 U5, C/2001 Q4 (NEAT), C/2009 R1, C/1956 R1, and C/2007 F1 (LONEOS).

Some authorities use the term "periodic comet" to refer to any comet with a periodic orbit (that is, all short-period comets plus all long-period comets), whereas others use it to mean exclusively short-period comets. Similarly, although the literal meaning of "non-periodic comet" is the same as "single-apparition comet", some use it to mean all comets that are not "periodic" in the second sense (that is, to include all comets with a period greater than 200 years).

Early observations have revealed a few genuinely hyperbolic (i.e. non-periodic) trajectories, but no more than could be accounted for by perturbations from Jupiter. Comets from interstellar space are moving with velocities of the same order as the relative velocities of stars near the Sun (a few tens of km per second). When such objects enter the Solar System, they have a positive specific orbital energy resulting in a positive velocity at infinity ($$v_{\infty}\!$$) and have notably hyperbolic trajectories. A rough calculation shows that there might be four hyperbolic comets per century within Jupiter's orbit, give or take one and perhaps two orders of magnitude.

Oort cloud and Hills cloud

The Oort cloud is thought to occupy a vast space starting from between 2000 and 5000 AU to as far as 50000 AU from the Sun. This cloud encases the celestial bodies that start at the middle of the Solar System—the Sun, all the way to outer limits of the Kuiper Belt. The Oort cloud consists of viable materials necessary for the creation of celestial bodies. The Solar System's planets exist only because of the planetesimals (chunks of leftover space that assisted in the creation of planets) that were condensed and formed by the gravity of the Sun. The eccentric made from these trapped planetesimals is why the Oort Cloud even exists. Some estimates place the outer edge at between 100000 and 200000 AU. The region can be subdivided into a spherical outer Oort cloud of 20000 - 50000 AU, and a doughnut-shaped inner cloud, the Hills cloud, of 2000 - 20000 AU. The outer cloud is only weakly bound to the Sun and supplies the long-period (and possibly Halley-type) comets that fall to inside the orbit of Neptune. The inner Oort cloud is also known as the Hills cloud, named after Jack G. Hills, who proposed its existence in 1981. Models predict that the inner cloud should have tens or hundreds of times as many cometary nuclei as the outer halo;  it is seen as a possible source of new comets that resupply the relatively tenuous outer cloud as the latter's numbers are gradually depleted. The Hills cloud explains the continued existence of the Oort cloud after billions of years.

Exocomets
Exocomets beyond the Solar System have been detected and may be common in the Milky Way. The first exocomet system detected was around Beta Pictoris, a very young A-type main-sequence star, in 1987. A total of 11 such exocomet systems have been identified, using the absorption spectrum caused by the large clouds of gas emitted by comets when passing close to their star. For ten years the Kepler space telescope was responsible for searching for planets and other forms outside of the solar system. The first transiting exocomets were found in February 2018 by a group consisting of professional astronomers and citizen scientists in light curves recorded by the Kepler Space Telescope. After Kepler Space Telescope retired in October 2018, a new telescope called TESS Telescope has taken over Kepler's mission. Since the launch of TESS, astronomers have discovered the transits of comets around the star Beta Pictoris using a light curve from TESS. Since TESS has taken over, astronomers have since been able to better distinguish exocomets with the spectroscopic method. New planets are detected by the white light curve method which is viewed as a symmetrical dip in the charts readings when a planet overshadows its parent star. However, after further evaluation of these light curves, it has been discovered that the asymmetrical patterns of the dips presented are caused by the tail of a comet or of hundreds of comets.

Connection to meteor showers
As a comet is heated during close passes to the Sun, outgassing of its icy components releases solid debris too large to be swept away by radiation pressure and the solar wind. If Earth's orbit sends it through that trail of debris, which is composed mostly of fine grains of rocky material, there is likely to be a meteor shower as Earth passes through. Denser trails of debris produce quick but intense meteor showers and less dense trails create longer but less intense showers. Typically, the density of the debris trail is related to how long ago the parent comet released the material. The Perseid meteor shower, for example, occurs every year between 9 and 13 August, when Earth passes through the orbit of Comet Swift–Tuttle. Halley's Comet is the source of the Orionid shower in October.

Comets and impact on life
Many comets and asteroids collided with Earth in its early stages. Many scientists think that comets bombarding the young Earth about 4 billion years ago brought the vast quantities of water that now fill Earth's oceans, or at least a significant portion of it. Others have cast doubt on this idea. The detection of organic molecules, including polycyclic aromatic hydrocarbons, in significant quantities in comets has led to speculation that comets or meteorites may have brought the precursors of life—or even life itself—to Earth. In 2013 it was suggested that impacts between rocky and icy surfaces, such as comets, had the potential to create the amino acids that make up proteins through shock synthesis. The speed at which the comets entered the atmosphere, combined with the magnitude of energy created after initial contact, allowed smaller molecules to condense into the larger macro-molecules that served as the foundation for life. In 2015, scientists found significant amounts of molecular oxygen in the outgassings of comet 67P, suggesting that the molecule may occur more often than had been thought, and thus less an indicator of life as has been supposed.

It is suspected that comet impacts have, over long timescales, delivered significant quantities of water to Earth's Moon, some of which may have survived as lunar ice. Comet and meteoroid impacts are thought to be responsible for the existence of tektites and australites.

Fear of comets
Fear of comets as acts of God and signs of impending doom was highest in Europe from AD 1200 to 1650. The year after the Great Comet of 1618, for example, Gotthard Arthusius published a pamphlet stating that it was a sign that the Day of Judgment was near. He listed ten pages of comet-related disasters, including "earthquakes, floods, changes in river courses, hail storms, hot and dry weather, poor harvests, epidemics, war and treason and high prices".

By 1700 most scholars concluded that such events occurred whether a comet was seen or not. Using Edmond Halley's records of comet sightings, however, William Whiston in 1711 wrote that the Great Comet of 1680 had a periodicity of 574 years and was responsible for the worldwide flood in the Book of Genesis, by pouring water on Earth. His announcement revived for another century fear of comets, now as direct threats to the world instead of signs of disasters. Spectroscopic analysis in 1910 found the toxic gas cyanogen in the tail of Halley's Comet, causing panicked buying of gas masks and quack "anti-comet pills" and "anti-comet umbrellas" by the public.

Departure (ejection) from Solar System
If a comet is traveling fast enough, it may leave the Solar System. Such comets follow the open path of a hyperbola, and as such, they are called hyperbolic comets. Solar comets are only known to be ejected by interacting with another object in the Solar System, such as Jupiter. An example of this is Comet C/1980 E1, which was shifted from an orbit of 7.1 million years around the Sun, to a hyperbolic trajectory, after a 1980 close pass by the planet Jupiter. Interstellar comets such as 1I/ʻOumuamua and 2I/Borisov never orbited the Sun and therefore do not require a 3rd-body interaction to be ejected from the Solar System.

Extinction
Jupiter-family comets and long-period comets appear to follow very different fading laws. The JFCs are active over a lifetime of about 10,000 years or ~1,000 orbits whereas long-period comets fade much faster. Only 10% of the long-period comets survive more than 50 passages to small perihelion and only 1% of them survive more than 2,000 passages. Eventually most of the volatile material contained in a comet nucleus evaporates, and the comet becomes a small, dark, inert lump of rock or rubble that can resemble an asteroid. Some asteroids in elliptical orbits are now identified as extinct comets. Roughly six percent of the near-Earth asteroids are thought to be extinct comet nuclei.

Breakup and collisions
The nucleus of some comets may be fragile, a conclusion supported by the observation of comets splitting apart. A significant cometary disruption was that of Comet Shoemaker–Levy 9, which was discovered in 1993. A close encounter in July 1992 had broken it into pieces, and over a period of six days in July 1994, these pieces fell into Jupiter's atmosphere—the first time astronomers had observed a collision between two objects in the Solar System. Other splitting comets include 3D/Biela in 1846 and 73P/Schwassmann–Wachmann from 1995 to 2006. Greek historian Ephorus reported that a comet split apart as far back as the winter of 372–373 BC. Comets are suspected of splitting due to thermal stress, internal gas pressure, or impact.

Comets 42P/Neujmin and 53P/Van Biesbroeck appear to be fragments of a parent comet. Numerical integrations have shown that both comets had a rather close approach to Jupiter in January 1850, and that, before 1850, the two orbits were nearly identical. Another group of comets that is the result of fragmentation episodes is the Liller comet family made of C/1988 A1 (Liller), C/1996 Q1 (Tabur), C/2015 F3 (SWAN), C/2019 Y1 (ATLAS), and C/2023 V5 (Leonard).

Some comets have been observed to break up during their perihelion passage, including great comets West and Ikeya–Seki. Biela's Comet was one significant example when it broke into two pieces during its passage through the perihelion in 1846. These two comets were seen separately in 1852, but never again afterward. Instead, spectacular meteor showers were seen in 1872 and 1885 when the comet should have been visible. A minor meteor shower, the Andromedids, occurs annually in November, and it is caused when Earth crosses the orbit of Biela's Comet.

Some comets meet a more spectacular end – either falling into the Sun or smashing into a planet or other body. Collisions between comets and planets or moons were common in the early Solar System: some of the many craters on the Moon, for example, may have been caused by comets. A recent collision of a comet with a planet occurred in July 1994 when Comet Shoemaker–Levy 9 broke up into pieces and collided with Jupiter.

Nomenclature

The names given to comets have followed several different conventions over the past two centuries. Prior to the early 20th century, most comets were referred to by the year when they appeared, sometimes with additional adjectives for particularly bright comets; thus, the "Great Comet of 1680", the "Great Comet of 1882", and the "Great January Comet of 1910".

After Edmond Halley demonstrated that the comets of 1531, 1607, and 1682 were the same body and successfully predicted its return in 1759 by calculating its orbit, that comet became known as Halley's Comet. Similarly, the second and third known periodic comets, Encke's Comet and Biela's Comet, were named after the astronomers who calculated their orbits rather than their original discoverers. Later, periodic comets were usually named after their discoverers, but comets that had appeared only once continued to be referred to by the year of their appearance.

In the early 20th century, the convention of naming comets after their discoverers became common, and this remains so today. A comet can be named after its discoverers or an instrument or program that helped to find it. For example, in 2019, astronomer Gennadiy Borisov observed a comet that appeared to have originated outside of the solar system; the comet was named 2I/Borisov after him.

Early observations and thought

From ancient sources, such as Chinese oracle bones, it is known that comets have been noticed by humans for millennia. Until the sixteenth century, comets were usually considered bad omens of deaths of kings or noble men, or coming catastrophes, or even interpreted as attacks by heavenly beings against terrestrial inhabitants.

Aristotle (384–322 BC) was the first known scientist to use various theories and observational facts to employ a consistent, structured cosmological theory of comets. He believed that comets were atmospheric phenomena, due to the fact that they could appear outside of the zodiac and vary in brightness over the course of a few days. Aristotle's cometary theory arose from his observations and cosmological theory that everything in the cosmos is arranged in a distinct configuration. Part of this configuration was a clear separation between the celestial and terrestrial, believing comets to be strictly associated with the latter. According to Aristotle, comets must be within the sphere of the moon and clearly separated from the heavens. Also in the 4th century BC, Apollonius of Myndus supported the idea that comets moved like the planets. Aristotelian theory on comets continued to be widely accepted throughout the Middle Ages, despite several discoveries from various individuals challenging aspects of it.

In the 1st century AD, Seneca the Younger questioned Aristotle's logic concerning comets. Because of their regular movement and imperviousness to wind, they cannot be atmospheric, and are more permanent than suggested by their brief flashes across the sky. He pointed out that only the tails are transparent and thus cloudlike, and argued that there is no reason to confine their orbits to the zodiac. In criticizing Apollonius of Myndus, Seneca argues, "A comet cuts through the upper regions of the universe and then finally becomes visible when it reaches the lowest point of its orbit." While Seneca did not author a substantial theory of his own, his arguments would spark much debate among Aristotle's critics in the 16th and 17th centuries.

In the 1st century AD, Pliny the Elder believed that comets were connected with political unrest and death. Pliny observed comets as "human like", often describing their tails with "long hair" or "long beard". His system for classifying comets according to their color and shape was used for centuries.

In India, by the 6th century AD astronomers believed that comets were apparitions that re-appeared periodically. This was the view expressed in the 6th century by the astronomers Varāhamihira and Bhadrabahu, and the 10th-century astronomer Bhaṭṭotpala listed the names and estimated periods of certain comets, but it is not known how these figures were calculated or how accurate they were.

There is a claim that an Arab scholar in 1258 noted several recurrent appearances of a comet (or a type of comet), and though it's not clear if he considered it to be a single periodic comet, it might have been a comet with a period of around 63 years.

In 1301, the Italian painter Giotto was the first person to accurately and anatomically portray a comet. In his work Adoration of the Magi, Giotto's depiction of Halley's Comet in the place of the Star of Bethlehem would go unmatched in accuracy until the 19th century and be bested only with the invention of photography.

Astrological interpretations of comets proceeded to take precedence clear into the 15th century, despite the presence of modern scientific astronomy beginning to take root. Comets continued to forewarn of disaster, as seen in the Luzerner Schilling chronicles and in the warnings of Pope Callixtus III. In 1578, German Lutheran bishop Andreas Celichius defined comets as "the thick smoke of human sins ... kindled by the hot and fiery anger of the Supreme Heavenly Judge". The next year, Andreas Dudith stated that "If comets were caused by the sins of mortals, they would never be absent from the sky."

Scientific approach
Crude attempts at a parallax measurement of Halley's Comet were made in 1456, but were erroneous. Regiomontanus was the first to attempt to calculate diurnal parallax by observing the Great Comet of 1472. His predictions were not very accurate, but they were conducted in the hopes of estimating the distance of a comet from Earth.

In the 16th century, Tycho Brahe and Michael Maestlin demonstrated that comets must exist outside of Earth's atmosphere by measuring the parallax of the Great Comet of 1577. Within the precision of the measurements, this implied the comet must be at least four times more distant than from Earth to the Moon. Based on observations in 1664, Giovanni Borelli recorded the longitudes and latitudes of comets that he observed, and suggested that cometary orbits may be parabolic. Despite being a skilled astronomer, in his 1623 book The Assayer, Galileo Galilei rejected Brahe's theories on the parallax of comets and claimed that they may be a mere optical illusion, despite little personal observation. In 1625, Maestlin's student Johannes Kepler upheld that Brahe's view of cometary parallax was correct. Additionally, mathematician Jacob Bernoulli published a treatise on comets in 1682.

During the early modern period comets were studied for their astrological significance in medical disciplines. Many healers of this time considered medicine and astronomy to be inter-disciplinary and employed their knowledge of comets and other astrological signs for diagnosing and treating patients.

Isaac Newton, in his Principia Mathematica of 1687, proved that an object moving under the influence of gravity by an inverse square law must trace out an orbit shaped like one of the conic sections, and he demonstrated how to fit a comet's path through the sky to a parabolic orbit, using the comet of 1680 as an example. He describes comets as compact and durable solid bodies moving in oblique orbit and their tails as thin streams of vapor emitted by their nuclei, ignited or heated by the Sun. He suspected that comets were the origin of the life-supporting component of air. He pointed out that comets usually appear near the Sun, and therefore most likely orbit it. On their luminosity, he stated, "The comets shine by the Sun's light, which they reflect," with their tails illuminated by "the Sun's light reflected by a smoke arising from [the coma]".

In 1705, Edmond Halley (1656–1742) applied Newton's method to 23 cometary apparitions that had occurred between 1337 and 1698. He noted that three of these, the comets of 1531, 1607, and 1682, had very similar orbital elements, and he was further able to account for the slight differences in their orbits in terms of gravitational perturbation caused by Jupiter and Saturn. Confident that these three apparitions had been three appearances of the same comet, he predicted that it would appear again in 1758–59. Halley's predicted return date was later refined by a team of three French mathematicians: Alexis Clairaut, Joseph Lalande, and Nicole-Reine Lepaute, who predicted the date of the comet's 1759 perihelion to within one month's accuracy. On 1758 November 14, Alexis Clairaut announced to the Royal Academy of Sciences in Paris his prediction of the date at which Halley's comet would return: On 1759 April 7, the French astronomer Joseph-Nicolas Delisle announced to the Royal Academy of Sciences in Paris that he and his assistant Charles Messier had observed the return of Halley's comet, as predicted: De l'Isle subsequently admitted that the comet's return had first been seen by a German amateur astronomer and farmer, Georg Palitzsch: The story behind the rediscovery of Halley's comet was given by Joseph Lalande in: See also:
 * Clairaut (January 1759) "Mémoire sur la cométe de 1682," Le Journal des Sçavans, pp. 38–45. On p. 44, Clairaut predicts that Halley's comet would return in mid April 1759. From p. 44 (translated from French): " ... it seems to me that the expected comet must pass its perihelion towards the middle of next April." On p. 40, Clairaut states that his prediction might be slightly incorrect due to the presence of unknown planets beyond Saturn: "A body [i.e., Halley's comet] which passes into regions so remote, and which escapes our eyes during such long intervals, might be subjected to totally unknown forces; such as the action of other comets, or even of some planet always too far from the sun to ever be perceived."
 * de l'Isle (June 1759) "Lettre de M. de l'Isle ... contenant la découverte du retour de la Comète de 1682, ... " (Letter from Mr. de l'Isle ... containing the discovery of the return of the comet of 1682), Le Journal des Sçavans, pp. 356–364.
 * de l'Isle (August 1759) "Seconde lettre de M. de l'Isle," Le Journal des Sçavans, pp. 523–529. From p. 526 (translated from French): " ... I received a letter from Heidelberg on the first of April in the evening, in which it is written to me that there had been published at Leipzig on the 24th of January of this year a German memoir in which it is said that this comet had been seen in Saxony by a peasant, named Palisch, on the 25th and 26th of December of last year; I can hardly conceive how this peasant could have discovered it, this comet ... "
 * Delalande, Tables astronomiques de M. Halley, ... Et l'Histoire de la Comete de 1759. [Astronomical tables of Mr. Halley, ... and the history of the comet of 1759.] (Paris, France: Durand, 1759), pp. 91 ff. Lalande acknowledged the contributions of Madame Lepaute to predicting the return of Halley's comet on p. 110. From p. 110 (translated from French): " ... but it must be admitted that this immense series of details would have seemed frightening to me if Madame LEPAUTE, [who has] long applied [herself] successfully to astronomical calculations, had not shared in the work."
 * Broughton, Peter (1985) "The first predicted return of comet Halley", Journal for the History of Astronomy, 16 : 123–132. Available at: Astrophysics Data System
 * Clairaut, du mouvement des comètes,'' ... [Theory of the movement of comets, ...] (Paris, France: Michel Lambert, 1760); see especially the preface. When the comet returned as predicted, it became known as Halley's Comet.

As early as the 18th century, some scientists had made correct hypotheses as to comets' physical composition. In 1755, Immanuel Kant hypothesized in his Universal Natural History that comets were condensed from "primitive matter" beyond the known planets, which is "feebly moved" by gravity, then orbit at arbitrary inclinations, and are partially vaporized by the Sun's heat as they near perihelion. In 1836, the German mathematician Friedrich Wilhelm Bessel, after observing streams of vapor during the appearance of Halley's Comet in 1835, proposed that the jet forces of evaporating material could be great enough to significantly alter a comet's orbit, and he argued that the non-gravitational movements of Encke's Comet resulted from this phenomenon.

In the 19th century, the Astronomical Observatory of Padova was an epicenter in the observational study of comets. Led by Giovanni Santini (1787–1877) and followed by Giuseppe Lorenzoni (1843–1914), this observatory was devoted to classical astronomy, mainly to the new comets and planets orbit calculation, with the goal of compiling a catalog of almost ten thousand stars. Situated in the Northern portion of Italy, observations from this observatory were key in establishing important geodetic, geographic, and astronomical calculations, such as the difference of longitude between Milan and Padua as well as Padua to Fiume. Correspondence within the observatory, particularly between Santini and another astronomer Giuseppe Toaldo, mentioned the importance of comet and planetary orbital observations.

In 1950, Fred Lawrence Whipple proposed that rather than being rocky objects containing some ice, comets were icy objects containing some dust and rock. This "dirty snowball" model soon became accepted and appeared to be supported by the observations of an armada of spacecraft (including the European Space Agency's Giotto probe and the Soviet Union's Vega 1 and Vega 2) that flew through the coma of Halley's Comet in 1986, photographed the nucleus, and observed jets of evaporating material.

On 22 January 2014, ESA scientists reported the detection, for the first definitive time, of water vapor on the dwarf planet Ceres, the largest object in the asteroid belt. The detection was made by using the far-infrared abilities of the Herschel Space Observatory. The finding is unexpected because comets, not asteroids, are typically considered to "sprout jets and plumes". According to one of the scientists, "The lines are becoming more and more blurred between comets and asteroids." On 11 August 2014, astronomers released studies, using the Atacama Large Millimeter/Submillimeter Array (ALMA) for the first time, that detailed the distribution of HCN, HNC, H2CO, and dust inside the comae of comets C/2012 F6 (Lemmon) and C/2012 S1 (ISON).

Spacecraft missions

 * The Halley Armada describes the collection of spacecraft missions that visited and/or made observations of Halley's Comet 1980s perihelion. The space shuttle Challenger was intended to do a study of Halley's Comet in 1986, but exploded shortly after being launched.
 * Deep Impact. Debate continues about how much ice is in a comet. In 2001, the Deep Space 1 spacecraft obtained high-resolution images of the surface of Comet Borrelly. It was found that the surface of comet Borrelly is hot and dry, with a temperature of between 26 and 71 C, and extremely dark, suggesting that the ice has been removed by solar heating and maturation, or is hidden by the soot-like material that covers Borrelly. In July 2005, the Deep Impact probe blasted a crater on Comet Tempel 1 to study its interior. The mission yielded results suggesting that the majority of a comet's water ice is below the surface and that these reservoirs feed the jets of vaporized water that form the coma of Tempel 1. Renamed EPOXI, it made a flyby of Comet Hartley 2 on 4 November 2010.
 * Ulysses. In 2007, the Ulysses probe unexpectedly passed through the tail of the comet C/2006 P1 (McNaught) which was discovered in 2006. Ulysses was launched in 1990 and the intended mission was for Ulysses to orbit around the Sun for further study at all latitudes.
 * Stardust. Data from the Stardust mission show that materials retrieved from the tail of Wild 2 were crystalline and could only have been "born in fire", at extremely high temperatures of over 1000 C. Although comets formed in the outer Solar System, radial mixing of material during the early formation of the Solar System is thought to have redistributed material throughout the proto-planetary disk. As a result, comets contain crystalline grains that formed in the early, hot inner Solar System. This is seen in comet spectra as well as in sample return missions. More recent still, the materials retrieved demonstrate that the "comet dust resembles asteroid materials". These new results have forced scientists to rethink the nature of comets and their distinction from asteroids.
 * Rosetta. The Rosetta probe orbited Comet Churyumov–Gerasimenko. On 12 November 2014, its lander Philae successfully landed on the comet's surface, the first time a spacecraft has ever landed on such an object in history.

Great comets

Approximately once a decade, a comet becomes bright enough to be noticed by a casual observer, leading such comets to be designated as great comets. Predicting whether a comet will become a great comet is notoriously difficult, as many factors may cause a comet's brightness to depart drastically from predictions. Broadly speaking, if a comet has a large and active nucleus, will pass close to the Sun, and is not obscured by the Sun as seen from Earth when at its brightest, it has a chance of becoming a great comet. However, Comet Kohoutek in 1973 fulfilled all the criteria and was expected to become spectacular but failed to do so. Comet West, which appeared three years later, had much lower expectations but became an extremely impressive comet.

The Great Comet of 1577 is a well-known example of a great comet. It passed near Earth as a non-periodic comet and was seen by many, including well-known astronomers Tycho Brahe and Taqi ad-Din. Observations of this comet led to several significant findings regarding cometary science, especially for Brahe.

The late 20th century saw a lengthy gap without the appearance of any great comets, followed by the arrival of two in quick succession—Comet Hyakutake in 1996, followed by Hale–Bopp, which reached maximum brightness in 1997 having been discovered two years earlier. The first great comet of the 21st century was C/2006 P1 (McNaught), which became visible to naked eye observers in January 2007. It was the brightest in over 40 years.

Sungrazing comets
A sungrazing comet is a comet that passes extremely close to the Sun at perihelion, generally within a few million kilometers. Although small sungrazers can be completely evaporated during such a close approach to the Sun, larger sungrazers can survive many perihelion passages. However, the strong tidal forces they experience often lead to their fragmentation.

About 90% of the sungrazers observed with SOHO are members of the Kreutz group, which all originate from one giant comet that broke up into many smaller comets during its first passage through the inner Solar System. The remainder contains some sporadic sungrazers, but four other related groups of comets have been identified among them: the Kracht, Kracht 2a, Marsden, and Meyer groups. The Marsden and Kracht groups both appear to be related to Comet 96P/Machholz, which is the parent of two meteor streams, the Quadrantids and the Arietids.

Unusual comets
Of the thousands of known comets, some exhibit unusual properties. Comet Encke (2P/Encke) orbits from outside the asteroid belt to just inside the orbit of the planet Mercury whereas the Comet 29P/Schwassmann–Wachmann currently travels in a nearly circular orbit entirely between the orbits of Jupiter and Saturn. 2060 Chiron, whose unstable orbit is between Saturn and Uranus, was originally classified as an asteroid until a faint coma was noticed. Similarly, Comet Shoemaker–Levy 2 was originally designated asteroid.

Largest
The largest known periodic comet is 95P/Chiron at 200 km in diameter that comes to perihelion every 50 years just inside of Saturn's orbit at 8 AU. The largest known Oort cloud comet is suspected of being Comet Bernardinelli-Bernstein at ≈150 km that will not come to perihelion until January 2031 just outside of Saturn's orbit at 11 AU. The Comet of 1729 is estimated to have been ≈100 km in diameter and came to perihelion inside of Jupiter's orbit at 4 AU.

Centaurs
Centaurs typically behave with characteristics of both asteroids and comets. Centaurs can be classified as comets such as 60558 Echeclus, and 166P/NEAT. 166P/NEAT was discovered while it exhibited a coma, and so is classified as a comet despite its orbit, and 60558 Echeclus was discovered without a coma but later became active, and was then classified as both a comet and an asteroid (174P/Echeclus). One plan for Cassini involved sending it to a centaur, but NASA decided to destroy it instead.

Observation
A comet may be discovered photographically using a wide-field telescope or visually with binoculars. However, even without access to optical equipment, it is still possible for the amateur astronomer to discover a sungrazing comet online by downloading images accumulated by some satellite observatories such as SOHO. SOHO's 2000th comet was discovered by Polish amateur astronomer Michał Kusiak on 26 December 2010 and both discoverers of Hale–Bopp used amateur equipment (although Hale was not an amateur).

Lost
A number of periodic comets discovered in earlier decades or previous centuries are now lost comets. Their orbits were never known well enough to predict future appearances or the comets have disintegrated. However, occasionally a "new" comet is discovered, and calculation of its orbit shows it to be an old "lost" comet. An example is Comet 11P/Tempel–Swift–LINEAR, discovered in 1869 but unobservable after 1908 because of perturbations by Jupiter. It was not found again until accidentally rediscovered by LINEAR in 2001. There are at least 18 comets that fit this category.

In popular culture
The depiction of comets in popular culture is firmly rooted in the long Western tradition of seeing comets as harbingers of doom and as omens of world-altering change. Halley's Comet alone has caused a slew of sensationalist publications of all sorts at each of its reappearances. It was especially noted that the birth and death of some notable persons coincided with separate appearances of the comet, such as with writers Mark Twain (who correctly speculated that he'd "go out with the comet" in 1910) and Eudora Welty, to whose life Mary Chapin Carpenter dedicated the song "Halley Came to Jackson".

In times past, bright comets often inspired panic and hysteria in the general population, being thought of as bad omens. More recently, during the passage of Halley's Comet in 1910, Earth passed through the comet's tail, and erroneous newspaper reports inspired a fear that cyanogen in the tail might poison millions, whereas the appearance of Comet Hale–Bopp in 1997 triggered the mass suicide of the Heaven's Gate cult.

In science fiction, the impact of comets has been depicted as a threat overcome by technology and heroism (as in the 1998 films Deep Impact and Armageddon), or as a trigger of global apocalypse (Lucifer's Hammer, 1979) or zombies (Night of the Comet, 1984). In Jules Verne's Off on a Comet a group of people are stranded on a comet orbiting the Sun, while a large crewed space expedition visits Halley's Comet in Sir Arthur C. Clarke's novel 2061: Odyssey Three.

In literature
The long-period comet first recorded by Pons in Florence on 15 July 1825 inspired Lydia Sigourney's humorous poem in which all the celestial bodies argue over the comet's appearance and purpose.

title: Comet


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Talk:The World Factbook

Albania as example of inaccuracies
I just removed the following from the factual inaccuracies section:
 * For example, Albania was until recently, described in the Factbook as Muslim 56.7%, Roman Catholic 10%, Orthodox 6.8%, atheist 2.5%, Bektashi 2.1%, other 5.7%, unspecified 16.2%, which was based on a survey conducted in 1939, before World War II; numerous surveys conducted since the fall of the Communist regime since 1990 have given quite different figures.

Those statistics are almost identical to the 2011 Albanian census figures cited at Albania, so close that I suspect it's ultimately the same data, with different rounding. It would be quite surprising if that 2011 census had the same findings as a 1939 one. Check the first reference, and the Factbook is indeed now sourcing its numbers to the 2011 census. The second reference doesn't discuss the Factbook or anything directly related to the idea of it citing old data. My guess is that at one time, the Factbook did indeed cite erroneous numbers via relying on a much older survey, but that's not a claim we can support on the weight of these sources.

I'm leaving all this here in case someone comes across a reliable source that discusses this, so they don't have to start from scratch. It might be as simple as plugging in the "right" numbers, plus updated referencing. --BDD (talk) 13:34, 27 October 2021 (UTC)

Primary source based
I recall flagging the reliance of this article on the work itself, and did again because it seems unresolved. I know the agency's work is astonishing, but I can't cite me. ~ cygnis insignis 15:39, 19 January 2022 (UTC)

Chagos Archipelago: Neutral language needed
The section about the Chagos Archipelago (which includes a large U.S./U.K. military base on Diego Garcia island) uses judgmental language to portray the United States as unjust. Even if this is true, the evidence for that conclusion must be stated in neutral terms. The biased language is unclear and therefore confusing, e.g.:

The United States is behind both the excision of the Chagos Archipelago from Mauritian territory and the forcible expulsion of the Chagossians from their lands to establish a military base on one of the island of the archipelago, namely Diego Garcia.

 * Does "behind" mean that the United States performed these actions or supported them while other actors performed them? The vagueness of "behind" might make it a weasel word implying conspiracy.
 * The passage also seems to state that all Chagossians (presumably the people of the Chagos Archipelago) were expelled from the islands, not just from Diego Garcia.
 * A reader unfamiliar with the facts might conclude that the Chagossians were the ones who "established a military base on one of the island[s]".

That's how confusing this compound sentence is. — ℜ ob C. alias ALAROB 17:03, 15 March 2022 (UTC)

Scope of "territorial issues and controversies" section
Many of the entires on this list only cite the Factbook itself, as opposed to a secondary source describing it as controversial, so it appears to be much more like routine maintenance than anything controversial. Numberguy6 (talk) 16:48, 27 July 2023 (UTC)

FACEBOOK DALOD
FACEBOOK — Preceding unsigned comment added by 154.198.107.70 (talk) 01:55, 29 October 2023 (UTC)

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

title: Talk:The World Factbook


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Wikipedia:Status of the porting of the CIA World Factbook

There is now a 2010 CIA - The World Factbook available online. Most of our entries are from the 2000 edition. Anyone with a lot of time and a sense of purpose is encouraged to update licence article's with the new data. Please state the World Factbook year to which the country has been updated when updating this list (i.e. "updated to 2007" not "finished").

Pieces of information ported not country-by-country

 * Table of historical exchange rates
 * Abbreviations used in CIA World Factbook (2002 edition; not entirely ported to List of general acronyms)

Countries
Please annotate the list below with the current status of the port from the CIA web site to the Wikipedia

 A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

A

 * Afghanistan (updated to 2007) —Cronholm144 11:37, 15 August 2007 (UTC)
 * Akrotiri (updated to 2007) —Cronholm144 11:37, 15 August 2007 (UTC)
 * Albania (updated to 2007) —Cronholm144 15:25, 15 August 2007 (UTC)
 * Algeria (Updated to 2003) Regulus 11:05, 6 Sep 2003 (UTC)
 * American Samoa
 * Andorra
 * Angola (updated to 2003) Greenman 31 Oct 2003
 * Anguilla
 * Antarctica
 * Antigua and Barbuda
 * Arctic Ocean
 * Argentina
 * Armenia
 * Aruba
 * Ashmore and Cartier Islands
 * Atlantic Ocean
 * Australia
 * Austria
 * Azerbaijan

B

 * Bahamas, The
 * Bahrain
 * Baker Island
 * Bangladesh
 * Barbados
 * Belarus
 * Belgium
 * Belize
 * Benin (geography done)
 * Bermuda (updated all the stats in Economy of Bermuda by Scratchdawg 16:37, 16 February 2007 (UTC))
 * Bhutan
 * Bolivia
 * Bosnia and Herzegovina (partly 2000, partly 2003)
 * Botswana (updated to 2003) Greenman 2 Nov 2003
 * Bouvet Island
 * Brazil
 * British Indian Ocean Territory
 * British Virgin Islands (Geography updated to 2004)
 * Brunei
 * Bulgaria
 * Burkina Faso
 * Burma
 * Burundi

C

 * Cambodia
 * Cameroon
 * Canada
 * Cape Verde
 * Cayman Islands
 * Central African Republic
 * Chad
 * Chile
 * China
 * Christmas Island
 * Clipperton Island
 * Cocos (Keeling) Islands
 * Colombia
 * Comoros (just added, Aug. 1 '01)
 * Congo, Democratic Republic of the (updated to 2003) Greenman 31 Oct 2003
 * Congo, Republic of the
 * Cook Islands
 * Coral Sea Islands
 * Costa Rica
 * Ivory Coast
 * Croatia (updated to 2003)
 * Cuba
 * Curacao
 * Cyprus
 * Czech Republic

D

 * Denmark
 * Dhekelia
 * Djibouti
 * Dominica
 * Dominican Republic

E

 * Ecuador
 * Egypt
 * El Salvador
 * Equatorial Guinea
 * Eritrea (updated to 2006)
 * Estonia
 * Ethiopia (updated to 2006)
 * European Union

F

 * Falkland Islands (Islas Malvinas) (info as CIA factbook of 10 January, 2006, extended)
 * Faroe Islands
 * Fiji
 * Finland
 * France
 * French Polynesia
 * French Southern and Antarctic Lands

G

 * Gabon
 * Gambia, The
 * Gaza Strip See also: Palestine
 * Georgia (Updated to 2004)
 * Germany
 * Ghana
 * Gibraltar
 * Greece
 * Greenland

 * Grenada
 * Guam
 * Guatemala
 * Guernsey
 * Guinea
 * Guinea-Bissau
 * Guyana

H

 * Haiti
 * Heard Island and McDonald Islands
 * Holy See (Vatican City)
 * Honduras
 * Hong Kong
 * Howland Island
 * Hungary

I

 * Iceland
 * India (updated to 2003 (Transportation/Communication)
 * Indian Ocean
 * Indonesia
 * Iran
 * Iraq

 * Ireland
 * Isle of Man
 * Israel See also: Palestine
 * Italy

J

 * Jamaica
 * Jan Mayen
 * Japan
 * Jarvis Island
 * Jersey
 * Johnston Atoll
 * Jordan

K

 * Kazakhstan
 * Kenya
 * Kingman Reef
 * Kiribati
 * Korea, North
 * Korea, South
 * Kosovo
 * Kuwait
 * Kyrgyzstan

L

 * Laos
 * Latvia
 * Lebanon
 * Lesotho
 * Liberia
 * Libya
 * Liechtenstein
 * Lithuania
 * Luxembourg

M

 * Macau
 * Macedonia
 * Madagascar
 * Malawi
 * Malaysia
 * Maldives
 * Mali
 * Malta
 * Marshall Islands
 * Mauritania
 * Mauritius
 * Mayotte
 * Mexico
 * Micronesia, Federated States of
 * Midway Islands
 * Moldova
 * Monaco
 * Mongolia
 * Montenegro
 * Montserrat
 * Morocco
 * Mozambique (updated to 2003) Greenman 8 Nov 2003

N

 * Namibia (updated to 2003) Greenman 2 Nov 2003
 * Nauru
 * Navassa Island
 * Nepal
 * Netherlands
 * New Caledonia
 * New Zealand (Updated to 2003) RossA 07:07, 11 Dec 2003 (UTC)
 * Nicaragua
 * Niger
 * Nigeria
 * Niue
 * Norfolk Island
 * Northern Mariana Islands
 * Norway

O

 * Oman

P

 * Pacific Ocean
 * Pakistan
 * Palau
 * Palmyra Atoll
 * Panama
 * Papua New Guinea (geography updated)
 * Paracel Islands
 * Paraguay
 * Peru
 * Philippines
 * Pitcairn Islands
 * Poland
 * Portugal
 * Puerto Rico

Q

 * Qatar

R

 * Romania
 * Russia
 * Rwanda

S

 * Saint Barthelemy
 * Saint Helena, Ascension, and Tristan da Cunha
 * Saint Kitts and Nevis
 * Saint Lucia
 * Saint Martin
 * Saint Pierre and Miquelon
 * Saint Vincent and the Grenadines
 * Samoa
 * San Marino
 * São Tomé and Príncipe
 * Saudi Arabia
 * Senegal

 * Serbia - almost updated to 2003 data; have not done demographics or government) —The preceding unsigned comment was added by Hoshie (talk • contribs).
 * Seychelles
 * Sierra Leone (updated to 2003) Greenman 15 November 2003
 * Singapore
 * Sint Maarten
 * Slovakia
 * Slovenia
 * Solomon Islands
 * Somalia
 * South Africa
 * South Georgia and South Sandwich Islands
 * Southern Ocean
 * South Sudan
 * Spain
 * Spratly Islands
 * Sri Lanka
 * Sudan
 * Suriname
 * Svalbard
 * Swaziland (updated to 2003) Greenman 12 Nov 2003
 * Sweden
 * Switzerland
 * Syria

T

 * Taiwan
 * Tajikistan
 * Tanzania
 * Thailand
 * Timor-Leste
 * Togo
 * Tokelau
 * Tonga
 * Trinidad and Tobago (updated to 2008) Christianwelsh 25 April 2008
 * Tunisia
 * Turkey
 * Turkmenistan
 * Turks and Caicos Islands
 * Tuvalu

U

 * Uganda
 * Ukraine
 * United Arab Emirates
 * United Kingdom
 * United States
 * United States Pacific Island Wildlife Refuges
 * Uruguay
 * Uzbekistan

V

 * Vanuatu
 * Venezuela
 * Vietnam
 * Virgin Islands (updated all to 2010 Gruepig (talk) 08:02, 22 November 2010 (UTC))

W

 * Wake Island
 * Wallis and Futuna
 * West Bank See also: Palestine
 * Western Sahara
 * "World" entry under Earth

Y

 * Yemen

Z

 * Zambia (updated to 2003) Greenman 13 Dec 2003
 * Zimbabwe (updated to 2003) Greenman 13 Nov 2003

Naming issues:

 * East Timor - entry is under Timor-Leste
 * Myanmar - entry is under Burma
 * Palestine - separate entries under West Bank and Gaza Strip
 * Republic of Macedonia - entry is under Macedonia

The Department of State info is at http://www.state.gov/r/pa/bgn/ ; I'm going about adding that alphabetically, as well; it's taking some time because not all of the text can be cut and pasted directly, at least not without looking sloppy. Much of it has to be integrated or left unadded, and some of their information, oddly enough, conflicts with the CIA info, esp. in re: economic figures. The status of that is here

 * See also : CIA World Factbook

Environmental Agreements
(Appendix C in the CIA World Factbook)
 * Basel Convention - updated to
 * Convention on Biological Diversity - updated to
 * Convention on Fishing and Conservation of Living Resources of the High Seas - updated to
 * Convention on Long-Range Transboundary Air Pollution - updated to
 * Nitrogen Oxide Protocol - updated to
 * POP Air Pollution Protocol - updated to
 * Sulphur Emissions Reduction Protocol - updated to
 * Volatile Organic Compounds Protocol - updated to
 * Convention on the International Trade in Endangered Species of Wild Flora and Fauna - updated to
 * Convention on the Prevention of Marine Pollution by Dumping Wastes and Other Matter - updated to
 * Convention on the Prohibition of Military or Any Other Hostile Use of Environmental Modification Techniques - updated to
 * Convention on Wetlands of International Importance Especially As Waterfowl Habitat - updated to
 * International Convention for the Regulation of Whaling - updated to
 * International Tropical Timber Agreement, 1983 - updated to
 * International Tropical Timber Agreement, 1994 - updated to
 * Montreal Protocol on Substances That Deplete the Ozone Layer - updated to
 * Protocol of 1978 Relating to the International Convention for the Prevention of Pollution From Ships, 1973 - updated to
 * Protocol on Environmental Protection to the Antarctic Treaty - updated to
 * Treaty Banning Nuclear Weapon Tests in the Atmosphere, in Outer Space, and Under Water - updated to
 * United Nations Convention on the Law of the Sea - updated to
 * United Nations Convention to Combat Desertification - updated to
 * United Nations Framework Convention on Climate Change - updated to


text:
Compost

Compost is a mixture of ingredients used as plant fertilizer and to improve soil's physical, chemical, and biological properties. It is commonly prepared by decomposing plant and food waste, recycling organic materials, and manure. The resulting mixture is rich in plant nutrients and beneficial organisms, such as bacteria, protozoa, nematodes, and fungi. Compost improves soil fertility in gardens, landscaping, horticulture, urban agriculture, and organic farming, reducing dependency on commercial chemical fertilizers. The benefits of compost include providing nutrients to crops as fertilizer, acting as a soil conditioner, increasing the humus or humic acid contents of the soil, and introducing beneficial microbes that help to suppress pathogens in the soil and reduce soil-borne diseases.

At the simplest level, composting requires gathering a mix of "greens" (green waste) and "browns" (brown waste). Greens are materials rich in nitrogen, such as leaves, grass, and food scraps. Browns are woody materials rich in carbon, such as stalks, paper, and wood chips. The materials break down into humus in a process taking months. Composting can be a multistep, closely monitored process with measured inputs of water, air, and carbon- and nitrogen-rich materials. The decomposition process is aided by shredding the plant matter, adding water, and ensuring proper aeration by regularly turning the mixture in a process using open piles or windrows. Fungi, earthworms, and other detritivores further break up the organic material. Aerobic bacteria and fungi manage the chemical process by converting the inputs into heat, carbon dioxide, and ammonium ions. Composting is an important part of waste management, since food and other compostable materials make up about 20% of waste in landfills, and due to anaerobic conditions, these materials take longer to biodegrade in the landfill. Composting offers an environmentally superior alternative to using organic material for landfill because composting reduces methane emissions due to anaerobic conditions, and provides economic and environmental co-benefits. For example, compost can also be used for land and stream reclamation, wetland construction, and landfill cover.

Fundamentals

Composting is an aerobic method of decomposing organic solid wastes, so it can be used to recycle organic material. The process involves decomposing organic material into a humus-like material, known as compost, which is a good fertilizer for plants.

Composting organisms require four equally important ingredients to work effectively:
 * Carbon is needed for energy; the microbial oxidation of carbon produces the heat required for other parts of the composting process. High carbon materials tend to be brown and dry.
 * Nitrogen is needed to grow and reproduce more organisms to oxidize the carbon. High nitrogen materials tend to be green and wet. They can also include colourful fruits and vegetables.
 * Oxygen is required for oxidizing the carbon, the decomposition process. Aerobic bacteria need oxygen levels above 5% to perform the processes needed for composting.
 * Water is necessary in the right amounts to maintain activity without causing locally anaerobic conditions.

Certain ratios of these materials allow microorganisms to work at a rate that will heat up the compost pile. Active management of the pile (e.g., turning over the compost heap) is needed to maintain sufficient oxygen and the right moisture level. The air/water balance is critical to maintaining high temperatures 130–160 F until the materials are broken down.

Composting is most efficient with a carbon-to-nitrogen ratio of about 25:1. Hot composting focuses on retaining heat to increase the decomposition rate, thus producing compost more quickly. Rapid composting is favored by having a carbon-to-nitrogen ratio of about 30 carbon units or less. Above 30, the substrate is nitrogen starved. Below 15, it is likely to outgas a portion of nitrogen as ammonia.

Nearly all dead plant and animal materials have both carbon and nitrogen in different amounts. Fresh grass clippings have an average ratio of about 15:1 and dry autumn leaves about 50:1 depending upon species. Composting is an ongoing and dynamic process; adding new sources of carbon and nitrogen consistently, as well as active management, is important.

Organisms
Organisms can break down organic matter in compost if provided with the correct mixture of water, oxygen, carbon, and nitrogen. They fall into two broad categories: chemical decomposers, which perform chemical processes on the organic waste, and physical decomposers, which process the waste into smaller pieces through methods such as grinding, tearing, chewing, and digesting.

Chemical decomposers

 * Bacteria are the most abundant and important of all the microorganisms found in compost. Bacteria process carbon and nitrogen and excrete plant-available nutrients such as nitrogen, phosphorus, and magnesium. Depending on the phase of composting, mesophilic or thermophilic bacteria may be the most prominent.
 * Mesophilic bacteria get compost to the thermophilic stage through oxidation of organic material. Afterwards they cure it, which makes the fresh compost more bioavailable for plants.
 * Thermophilic bacteria do not reproduce and are not active between -5 and 25 C, yet are found throughout soil. They activate once the mesophilic bacteria have begun to break down organic matter and increase the temperature to their optimal range. They have been shown to enter soils via rainwater. They are present so broadly because of many factors, including their spores being resilient. Thermophilic bacteria thrive at higher temperatures, reaching 40 – in typical mixes. Large-scale composting operations, such as windrow composting, may exceed this temperature, potentially killing beneficial soil microorganisms but also pasteurizing the waste.
 * Actinomycetota are needed to break down paper products such as newspaper, bark, etc., and other large molecules such as lignin and cellulose that are more difficult to decompose. The "pleasant, earthy smell of compost" is attributed to Actinomycetota. They make carbon, ammonia, and nitrogen nutrients available to plants.
 * Fungi such as molds and yeasts help break down materials that bacteria cannot, especially cellulose and lignin in woody material.
 * Protozoa contribute to biodegradation of organic matter and consume inactive bacteria, fungi, and micro-organic particulates.

Physical decomposers

 * Ants create nests, making the soil more porous and transporting nutrients to different areas of the compost.
 * Beetles as grubs feed on decaying vegetables.
 * Earthworms ingest partly composted material and excrete worm castings, making nitrogen, calcium, phosphorus, and magnesium available to plants. The tunnels they create as they move through the compost also increase aeration and drainage.
 * Flies feed on almost all organic material and put bacteria into the compost. Their population is kept in check by mites and the thermophilic temperatures that are unsuitable for fly larvae.
 * Millipedes break down plant material.
 * Rotifers feed on plant particles.
 * Snails and slugs feed on living or fresh plant material. They should be removed from compost before use, as they can damage plants and crops.
 * Sow bugs feed on rotting wood and decaying vegetation.
 * Springtails feed on fungi, molds, and decomposing plants.

Phases of composting
Under ideal conditions, composting proceeds through three major phases:
 * 1) Mesophilic phase: The initial, mesophilic phase is when the decomposition is carried out under moderate temperatures by mesophilic microorganisms.
 * 2) Thermophilic phase: As the temperature rises, a second, thermophilic phase starts, in which various thermophilic bacteria carry out the decomposition under higher temperatures (50 to 60 C.)
 * 3) Maturation phase: As the supply of high-energy compounds dwindles, the temperature starts to decrease, and the mesophilic bacteria once again predominate in the maturation phase.

Hot and cold composting – impact on timing
The time required to compost material relates to the volume of material, the particle size of the inputs (e.g. wood chips break down faster than branches), and the amount of mixing and aeration. Generally, larger piles reach higher temperatures and remain in a thermophilic stage for days or weeks. This is hot composting and is the usual method for large-scale municipal facilities and agricultural operations.

The Berkeley method produces finished compost in 18 days. It requires assembly of at least 1 m3 of material at the outset and needs turning every two days after an initial four-day phase. Such short processes involve some changes to traditional methods, including smaller, more homogenized particle sizes in the input materials, controlling carbon-to-nitrogen ratio (C:N) at 30:1 or less, and careful monitoring of the moisture level.

Cold composting is a slower process that can take up to a year to complete. It results from smaller piles, including many residential compost piles that receive small amounts of kitchen and garden waste over extended periods. Piles smaller than 1 m3 tend not to reach and maintain high temperatures. Turning is not necessary with cold composting, although a risk exists that parts of the pile may go anaerobic as it becomes compacted or waterlogged.

Pathogen removal
Composting can destroy some pathogens and seeds, by reaching temperatures above 50 C. Dealing with stabilized compost – i.e. composted material in which microorganisms have finished digesting the organic matter and the temperature has reached between 50 and 70 C – poses very little risk, as these temperatures kill pathogens and even make oocysts unviable. The temperature at which a pathogen dies depends on the pathogen, how long the temperature is maintained (seconds to weeks), and pH.

Compost products such as compost tea and compost extracts have been found to have an inhibitory effect on Fusarium oxysporum, Rhizoctonia species, and Pythium debaryanum, plant pathogens that can cause crop diseases. Aerated compost teas are more effective than compost extracts. The microbiota and enzymes present in compost extracts also have a suppressive effect on fungal plant pathogens. Compost is a good source of biocontrol agents like B. subtilis, B. licheniformis, and P. chrysogenum that fight plant pathogens. Sterilizing the compost, compost tea, or compost extracts reduces the effect of pathogen suppression.

Diseases that can be contracted from handling compost
When turning compost that has not gone through phases where temperatures above 50 C are reached, a mouth mask and gloves must be worn to protect from diseases that can be contracted from handling compost, including:
 * Aspergillosis
 * Farmer's lung
 * Histoplasmosis – a fungus that grows in guano and bird droppings
 * Legionnaires' disease
 * Paronychia – via infection around the fingernails and toenails
 * Tetanus – a central nervous system disease

Oocytes are rendered unviable by temperatures over 50 C.

Environmental benefits
Compost adds organic matter to the soil and increases the nutrient content and biodiversity of microbes in soil. Composting at home reduces the amount of green waste being hauled to dumps or composting facilities. The reduced volume of materials being picked up by trucks results in fewer trips, which in turn lowers the overall emissions from the waste-management fleet.

Materials that can be composted
Potential sources of compostable materials, or feedstocks, include residential, agricultural, and commercial waste streams. Residential food or yard waste can be composted at home, or collected for inclusion in a large-scale municipal composting facility. In some regions, it could also be included in a local or neighborhood composting project.

Organic solid waste

The two broad categories of organic solid waste are green and brown. Green waste is generally considered a source of nitrogen and includes pre- and post-consumer food waste, grass clippings, garden trimmings, and fresh leaves. Animal carcasses, roadkill, and butcher residue can also be composted, and these are considered nitrogen sources.

Brown waste is a carbon source. Typical examples are dried vegetation and woody material such as fallen leaves, straw, woodchips, limbs, logs, pine needles, sawdust, and wood ash, but not charcoal ash. Products derived from wood such as paper and plain cardboard are also considered carbon sources.

Animal manure and bedding
On many farms, the basic composting ingredients are animal manure generated on the farm as a nitrogen source, and bedding as the carbon source. Straw and sawdust are common bedding materials. Nontraditional bedding materials are also used, including newspaper and chopped cardboard. The amount of manure composted on a livestock farm is often determined by cleaning schedules, land availability, and weather conditions. Each type of manure has its own physical, chemical, and biological characteristics. Cattle and horse manures, when mixed with bedding, possess good qualities for composting. Swine manure, which is very wet and usually not mixed with bedding material, must be mixed with straw or similar raw materials. Poultry manure must be blended with high-carbon, low-nitrogen materials.

Human excreta
Human excreta, sometimes called "humanure" in the composting context, can be added as an input to the composting process since it is a nutrient-rich organic material. Nitrogen, which serves as a building block for important plant amino acids, is found in solid human waste. Phosphorus, which helps plants convert sunlight into energy in the form of ATP, can be found in liquid human waste.

Solid human waste can be collected directly in composting toilets, or indirectly in the form of sewage sludge after it has undergone treatment in a sewage treatment plant. Both processes require capable design, as potential health risks need to be managed. In the case of home composting, a wide range of microorganisms, including bacteria, viruses, and parasitic worms, can be present in feces, and improper processing can pose significant health risks. In the case of large sewage treatment facilities that collect wastewater from a range of residential, commercial and industrial sources, there are additional considerations. The composted sewage sludge, referred to as biosolids, can be contaminated with a variety of metals and pharmaceutical compounds. Insufficient processing of biosolids can also lead to problems when the material is applied to land.

Urine can be put on compost piles or directly used as fertilizer. Adding urine to compost can increase temperatures, so can increase its ability to destroy pathogens and unwanted seeds. Unlike feces, urine does not attract disease-spreading flies (such as houseflies or blowflies), and it does not contain the most hardy of pathogens, such as parasitic worm eggs.

Animal remains
Animal carcasses may be composted as a disposal option. Such material is rich in nitrogen.

Hügelkultur (raised garden beds or mounds)

The practice of making raised garden beds or mounds filled with rotting wood is also called Hügelkultur in German. It is in effect creating a nurse log that is covered with soil.

Benefits of Hügelkultur garden beds include water retention and warming of soil. Buried wood acts like a sponge as it decomposes, able to capture water and store it for later use by crops planted on top of the bed.

Related technologies

 * Vermicompost (also called worm castings, worm humus, worm manure, or worm faeces) is the end product of the breakdown of organic matter by earthworms. These castings have been shown to contain reduced levels of contaminants and a higher saturation of nutrients than the organic materials before vermicomposting.
 * Black soldier fly (Hermetia illucens) larvae are able to rapidly consume large amounts of organic material and can be used to treat human waste. The resulting compost still contains nutrients and can be used for biogas production, or further traditional composting or vermicomposting
 * Bokashi is a fermentation process rather than a decomposition process, and so retains the feedstock's energy, nutrient and carbon contents. There must be sufficient carbohydrate for fermentation to complete and therefore the process is typically applied to food waste, including noncompostable items. Carbohydrate is transformed into lactic acid, which dissociates naturally to form lactate, a biological energy carrier. The preserved result is therefore readily consumed by soil microbes and from there by the entire soil food web, leading to a significant increase in soil organic carbon and turbation. The process completes in weeks and returns soil acidity to normal.
 * Co-composting is a technique that processes organic solid waste together with other input materials such as dewatered fecal sludge or sewage sludge.
 * Anaerobic digestion combined with mechanical sorting of mixed waste streams is increasingly being used in developed countries due to regulations controlling the amount of organic matter allowed in landfills. Treating biodegradable waste before it enters a landfill reduces global warming from fugitive methane; untreated waste breaks down anaerobically in a landfill, producing landfill gas that contains methane, a potent greenhouse gas. The methane produced in an anaerobic digester can be used as biogas.

Agriculture and gardening
On open ground for growing wheat, corn, soybeans, and similar crops, compost can be broadcast across the top of the soil using spreader trucks or spreaders pulled behind a tractor. It is expected that the spread layer is very thin (approximately 6 mm) and worked into the soil prior to planting. Application rates of 25 mm or more are not unusual when trying to rebuild poor soils or control erosion. Due to the extremely high cost of compost per unit of nutrients in the United States, on-farm use is relatively rare since rates over 4 tons/acre may not be affordable. This results from an over-emphasis on "recycling organic matter" than on "sustainable nutrients." In countries such as Germany, where compost distribution and spreading are partially subsidized in the original waste fees, compost is used more frequently on open ground on the premise of nutrient "sustainability".

In plasticulture, strawberries, tomatoes, peppers, melons, and other fruits and vegetables are grown under plastic to control temperature, retain moisture and control weeds. Compost may be banded (applied in strips along rows) and worked into the soil prior to bedding and planting, be applied at the same time the beds are constructed and plastic laid down, or used as a top dressing.

Many crops are not seeded directly in the field but are started in seed trays in a greenhouse. When the seedlings reach a certain stage of growth, they are transplanted in the field. Compost may be part of the mix used to grow the seedlings, but is not normally used as the only planting substrate. The particular crop and the seeds' sensitivity to nutrients, salts, etc. dictates the ratio of the blend, and maturity is important to insure that oxygen deprivation will not occur or that no lingering phyto-toxins remain.

Compost can be added to soil, coir, or peat, as a tilth improver, supplying humus and nutrients. It provides a rich growing medium as absorbent material. This material contains moisture and soluble minerals, which provide support and nutrients. Although it is rarely used alone, plants can flourish from mixed soil that includes a mix of compost with other additives such as sand, grit, bark chips, vermiculite, perlite, or clay granules to produce loam. Compost can be tilled directly into the soil or growing medium to boost the level of organic matter and the overall fertility of the soil. Compost that is ready to be used as an additive is dark brown or even black with an earthy smell.

Generally, direct seeding into a compost is not recommended due to the speed with which it may dry, the possible presence of phytotoxins in immature compost that may inhibit germination,  and the possible tie up of nitrogen by incompletely decomposed lignin. It is very common to see blends of 20–30% compost used for transplanting seedlings.

Compost can be used to increase plant immunity to diseases and pests.

Compost tea
Compost tea is made up of extracts of fermented water leached from composted materials. Composts can be either aerated or non-aerated depending on its fermentation process. Compost teas are generally produced from adding compost to water in a ratio of 1:4–1:10, occasionally stirring to release microbes.

There is debate about the benefits of aerating the mixture. Non-aerated compost tea is cheaper and less labor intensive, but there are conflicting studies regarding the risks of phytotoxicity and human pathogen regrowth. Aerated compost tea brews faster and generates more microbes, but has potential for human pathogen regrowth, particularly when one adds additional nutrients to the mixture.

Field studies have shown the benefits of adding compost teas to crops due to organic matter input, increased nutrient availability, and increased microbial activity. They have also been shown to have a suppressive effect on plant pathogens and soil-borne diseases. The efficacy is influenced by a number of factors, such as the preparation process, the type of source the conditions of the brewing process, and the environment of the crops. Adding nutrients to compost tea can be beneficial for disease suppression, although it can trigger the regrowth of human pathogens like E. coli and Salmonella.

Compost extract
Compost extracts are unfermented or non-brewed extracts of leached compost contents dissolved in any solvent.

Commercial sale
Compost is sold as bagged potting mixes in garden centers and other outlets. This may include composted materials such as manure and peat but is also likely to contain loam, fertilizers, sand, grit, etc. Varieties include multi-purpose composts designed for most aspects of planting, John Innes formulations, grow bags, designed to have crops such as tomatoes directly planted into them. There are also a range of specialist composts available, e.g. for vegetables, orchids, houseplants, hanging baskets, roses, ericaceous plants, seedlings, potting on, etc.

Other
Compost can also be used for land and stream reclamation, wetland construction, and landfill cover.

The temperatures generated by compost can be used to heat greenhouses, such as by being placed around the outside edges.

Regulations
There are process and product guidelines in Europe that date to the early 1980s (Germany, the Netherlands, Switzerland) and only more recently in the UK and the US. In both these countries, private trade associations within the industry have established loose standards, some say as a stop-gap measure to discourage independent government agencies from establishing tougher consumer-friendly standards. Compost is regulated in Canada and Australia as well.

EPA Class A and B guidelines in the United States were developed solely to manage the processing and beneficial reuse of sludge, also now called biosolids, following the US EPA ban of ocean dumping. About 26 American states now require composts to be processed according to these federal protocols for pathogen and vector control, even though the application to non-sludge materials has not been scientifically tested. An example is that green waste composts are used at much higher rates than sludge composts were ever anticipated to be applied at. U.K guidelines also exist regarding compost quality, as well as Canadian, Australian, and the various European states.

In the United States, some compost manufacturers participate in a testing program offered by a private lobbying organization called the U.S. Composting Council. The USCC was originally established in 1991 by Procter & Gamble to promote composting of disposable diapers, following state mandates to ban diapers in landfills, which caused a national uproar. Ultimately the idea of composting diapers was abandoned, partly since it was not proven scientifically to be possible, and mostly because the concept was a marketing stunt in the first place. After this, composting emphasis shifted back to recycling organic wastes previously destined for landfills. There are no bonafide quality standards in America, but the USCC sells a seal called "Seal of Testing Assurance" (also called "STA"). For a considerable fee, the applicant may display the USCC logo on products, agreeing to volunteer to customers a current laboratory analysis that includes parameters such as nutrients, respiration rate, salt content, pH, and limited other indicators.

Many countries such as Wales and some individual cities such as Seattle and San Francisco require food and yard waste to be sorted for composting (San Francisco Mandatory Recycling and Composting Ordinance).

The USA is the only Western country that does not distinguish sludge-source compost from green-composts, and by default 50% of US states expect composts to comply in some manner with the federal EPA 503 rule promulgated in 1984 for sludge products.

There are health risk concerns about PFASs ("forever chemicals") levels in compost derived from sewage sledge sourced biosolids, and EPA has not set health risk standards for this. The Sierra Club recommends that home gardeners avoid the use of sewage sludge-base fertilizer and compost, in part due to potentially high levels of PFASs. The EPA PFAS Strategic Roadmap initiative, running from 2021 to 2024, will consider the full lifecycle of PFAS including health risks of PFAS in wastewater sludge.

History
Composting dates back to at least the early Roman Empire, and was mentioned as early as Cato the Elder's 160 BCE piece De Agri Cultura. Traditionally, composting involved piling organic materials until the next planting season, at which time the materials would have decayed enough to be ready for use in the soil. Methodologies for organic composting were part of traditional agricultural systems around the world.

Composting began to modernize somewhat from the 1920s in Europe as a tool for organic farming. The first industrial station for the transformation of urban organic materials into compost was set up in Wels, Austria in the year 1921. Early proponents of composting within farming include Rudolf Steiner, founder of a farming method called biodynamics, and Annie Francé-Harrar, who was appointed on behalf of the government in Mexico and supported the country in 1950–1958 to set up a large humus organization in the fight against erosion and soil degradation. Sir Albert Howard, who worked extensively in India on sustainable practices, and Lady Eve Balfour were also major proponents of composting. Modern scientific composting was imported to America by the likes of J. I. Rodale – founder of Rodale, Inc. Organic Gardening, and others involved in the organic farming movement.

Related lists

 * List of composting systems
 * List of environment topics
 * List of sustainable agriculture topics
 * List of organic gardening and farming topics

title: Compost


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Talk:Celtic languages

New hypothesis for the origin of the Celtic languages
New hypothesis for the origin of the Celtic languages: Article 173.88.246.138 (talk) 05:24, 1 January 2022 (UTC)

 * That article indicates that there is genetic evidence of a second major wave of Indo-European migration to Britain and that it’s related to Gauls. That is a good argument for the replacement of Q-Celtic speakers in Britain (i.e., the first IE wave of migration which continued on throughout Britain and Ireland) by P-Celtic speakers. Gortaleen (talk) 11:47, 14 February 2024 (UTC)
 * Very early days for this, & we wouldn't put anything in based on press reports. Linguists, archaeology & dna people tend not to see eye-to-eye on such matters, especially as neither digging nor dna analysis actually tell you what languages were spoken. Johnbod (talk) 11:56, 14 February 2024 (UTC)
 * I’m noting that editors should be prudent in claims made in the article. Traditional “history” - based ultimately on the Book of Invasions - is soon going to be upended by serious academics using genetic genealogy as data to help develop more reliable theories.
 * For example, see the Kurgan Hypothesis vs the theory of migration of Indo-European people circa 5000 years ago. Gortaleen (talk) 22:53, 14 February 2024 (UTC)

Pictish
On the list, "Possibly Celtic languages", i cut out Pictish on the grounds that it is pretty much known to be Celtic. Okay?--Solomonfromfinland (talk) 15:10, 20 January 2022 (UTC)

title: Talk:Celtic languages


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Capitol

A capitol, named after the Capitoline Hill in Rome, is usually a legislative building where a legislature meets and makes laws for its respective political entity.

Specific capitols include:
 * United States Capitol in Washington, D.C.
 * Numerous U.S. state and territorial capitols
 * Capitolio Nacional in Bogotá, Colombia
 * Capitolio Federal in Caracas, Venezuela
 * El Capitolio in Havana, Cuba
 * Capitol of Palau in Ngerulmud, Palau

Capitol, capitols, or The Capitol may also refer to:

 * Entertainment and Media
 * Capitol (board game), a Roman-themed board game
 * Capitol (The Hunger Games trilogy), a fictional city in The Hunger Games novels
 * Capitol (TV series), a U.S. soap opera
 * Capitol (collection), a book by Orson Scott Card
 * The Capitols, a Detroit, Michigan-based soul trio

 * Business
 * Capitol Wrestling Corporation, a predecessor organization to World Wrestling Entertainment
 * Capitol Records, a U.S. record label
 * Capitol Air, originally known as Capitol International Airways, an American charter airline operating from 1946 to the mid 1980s

 * Other locations
 * Capitoline Hill in Rome (from which the word capitol derives)
 * Capitols, former name of the Capitol Corridor passenger train route in California, United States
 * Capitole de Toulouse, a historic building in Toulouse, France, now used as a municipal and public-arts center
 * The capitouls of Toulouse, the city's former chief magistrates
 * Capitol College, a private, non-profit, and non-sectarian college located just south of Laurel, Maryland
 * Capitol Butte, a mountain in Arizona
 * Capitol Reef National Park, a U.S. National Park in south-central Utah
 * Capitolium, the temple for the Capitoline Triad in many cities of the Roman Empire
 * The Capitol (Hong Kong), a large private housing estate in Hong Kong
 * The Capitol (Fayetteville, North Carolina), department store
 * Capitol (Williamsburg, Virginia), a historic building that housed the House of Burgesses of the Colony of Virginia 1705–1779

title: Capitol