text:
Full moon

The full moon is the lunar phase when the Moon appears fully illuminated from Earth's perspective. This occurs when Earth is located between the Sun and the Moon (when the ecliptic longitudes of the Sun and Moon differ by 180°). This means that the lunar hemisphere facing Earth—the near side—is completely sunlit and appears as an approximately circular disk. The full moon occurs roughly once a month.

The time interval between a full moon and the next repetition of the same phase, a synodic month, averages about 29.53 days. Because of irregularities in the moon's orbit, the new and full moons may fall up to thirteen hours either side of their mean. If the calendar date is not locally determined through observation of the new moon at the beginning of the month there is the potential for a further twelve hours difference depending on the time zone. Potential discrepancies also arise from whether the calendar day is considered to begin in the evening or at midnight. It is normal for the full moon to fall on the fourteenth or the fifteenth of the month according to whether the start of the month is reckoned from the appearance of the new moon or from the conjunction. A tabular lunar calendar will also exhibit variations depending on the intercalation system used. Because a calendar month consists of a whole number of days, a month in a lunar calendar may be either 29 or 30 days long.

Characteristics
A full moon is often thought of as an event of a full night's duration, although its phase seen from Earth continuously waxes or wanes, and is full only at the instant when waxing ends and waning begins. For any given location, about half of these maximum full moons may be visible, while the other half occurs during the day, when the full moon is below the horizon. As the Moon's orbit is inclined by 5.145° from the ecliptic, it is not generally perfectly opposite from the Sun during full phase, therefore a full moon is in general not perfectly full except on nights with a lunar eclipse as the Moon crosses the ecliptic at opposition from the Sun.

Many almanacs list full moons not only by date, but also by their exact time, usually in Coordinated Universal Time (UTC). Typical monthly calendars that include lunar phases may be offset by one day when prepared for a different time zone.

The full moon is generally a suboptimal time for astronomical observation of the Moon because shadows vanish. It is a poor time for other observations because the bright sunlight reflected by the Moon, amplified by the opposition surge, then outshines many stars.

Moon phases
There are eight phases of the moon, which vary from partial to full illumination. The moon phases are also called lunar phases. These stages have different names that come from its shape and size at each phase. For example, the crescent moon is 'banana' shaped, and the half-moon is D-shaped. When the moon is nearly full, it is called a gibbous moon. The crescent and gibbous moons each last approximately a week.

Each phase is also described in accordance to its position on the full 29.5 day cycle. The eight phases of the moon in order:
 * new moon
 * waxing crescent moon
 * first quarter moon
 * waxing gibbous moon
 * full moon
 * waning gibbous moon
 * last quarter moon
 * waning crescent moon

Formula
The date and approximate time of a specific full moon (assuming a circular orbit) can be calculated from the following equation:
 * $$ d = 20.362000+ 29.530588861 \times N + 102.026 \times 10^{-12} \times N^2$$

where d is the number of days since 1 January 2000 00:00:00 in the Terrestrial Time scale used in astronomical ephemerides; for Universal Time (UT) add the following approximate correction to d:
 * $$-0.000739 - (235 \times 10^{-12})\times N^2$$ days

where N is the number of full moons since the first full moon of 2000. The true time of a full moon may differ from this approximation by up to about 14.5 hours as a result of the non-circularity of the Moon's orbit. See New moon for an explanation of the formula and its parameters.

The age and apparent size of the full moon vary in a cycle of just under 14 synodic months, which has been referred to as a full moon cycle.

Lunar eclipses
When the Moon moves into Earth's shadow, a lunar eclipse occurs, during which all or part of the Moon's face may appear reddish due to the Rayleigh scattering of blue wavelengths and the refraction of sunlight through Earth's atmosphere. Lunar eclipses happen only during a full moon and around points on its orbit where the satellite may pass through the planet's shadow. A lunar eclipse does not occur every month because the Moon's orbit is inclined 5.145° with respect to the ecliptic plane of Earth; thus, the Moon usually passes north or south of Earth's shadow, which is mostly restricted to this plane of reference. Lunar eclipses happen only when the full moon occurs around either node of its orbit (ascending or descending). Therefore, a lunar eclipse occurs about every six months, and often two weeks before or after a solar eclipse, which occurs during a new moon around the opposite node.

In folklore and tradition

In Buddhism, Vesak is celebrated on the full moon day of the Vaisakha month, marking the birth, enlightenment, and the death of the Buddha.

In Arabic, badr (بدر ) means 'full moon', but it is often translated as 'white moon', referring to The White Days, the three days when the full moon is celebrated.

Full moons are traditionally associated with insomnia (inability to sleep), insanity (hence the terms lunacy and lunatic) and various "magical phenomena" such as lycanthropy. Psychologists, however, have found that there is no strong evidence for effects on human behavior around the time of a full moon. They find that studies are generally not consistent, with some showing a positive effect and others showing a negative effect. In one instance, the 23 December 2000 issue of the British Medical Journal published two studies on dog bite admission to hospitals in England and Australia. The study of the Bradford Royal Infirmary found that dog bites were twice as common during a full moon, whereas the study conducted by the public hospitals in Australia found that they were less likely.

The symbol of the Triple Goddess is drawn with the circular image of the full moon in the center flanked by a left facing crescent and right facing crescent, on either side, representing a maiden, mother and crone archetype.

Full moon names
Historically, month names are names of moons (lunations, not necessarily full moons) in lunisolar calendars. Since the introduction of the solar Julian calendar in the Roman Empire, and later the Gregorian calendar worldwide, people no longer perceive month names as "moon" names. The traditional Old English month names were equated with the names of the Julian calendar from an early time, soon after Christianization, according to the testimony of Bede around AD 700.

Some full moons have developed new names in modern times, such as "blue moon", as well as "harvest moon" and "hunter's moon" for the full moons of autumn.

Lunar eclipses occur only at a full moon and often cause a reddish hue on the near side of the Moon. This full moon has been called a blood moon in popular culture.

Harvest and hunter's moons

The "harvest moon" and the "hunter's moon" are traditional names for the full moons in late summer and in the autumn in the Northern Hemisphere, usually in September and October, respectively. People may celebrate these occurrences in festivities such as the Chinese Mid-Autumn Festival, which is as important as the Chinese New Year.

The "harvest moon" (also known as the "barley moon" or "full corn moon") is the full moon nearest to the autumnal equinox (22 or 23 September), occurring anytime within two weeks before or after that date. The "hunter's moon" is the full moon following it. The names are recorded from the early 18th century. The Oxford English Dictionary entry for "harvest moon" cites a 1706 reference, and for "hunter's moon" a 1710 edition of The British Apollo, which attributes the term to "the country people" ("The Country People call this the Hunters-Moon.") The names became traditional in American folklore, where they are now often popularly attributed to Native Americans. The Feast of the Hunters' Moon is a yearly festival in West Lafayette, Indiana, held in late September or early October each year since 1968. In 2010 the harvest moon occurred on the night of the equinox itself (some 5$1⁄2$ hours after the moment of equinox) for the first time since 1991, after a period known as the Metonic cycle.

All full moons rise around the time of sunset. Since the Moon moves eastward among the stars faster than the Sun, lunar culmination is delayed by about 50.47 minutes (on average) each day, thus causing moonrise to occur later each day.

Due to the high lunar standstill, the harvest and hunter's moons of 2007 were special because the time difference between moonrises on successive evenings was much shorter than average. The moon rose about 30 minutes later from one night to the next, as seen from about 40° N or S latitude (because the full moon of September 2007 rose in the northeast rather than in the east). Hence, no long period of darkness occurred between sunset and moonrise for several days after the full moon, thus lengthening the time in the evening when there is enough twilight and moonlight to work to get the harvest in.

Native American
Various 18th and 19th century writers gave what were claimed to be Native American or First Nations moon names. These were not the names of the full moons as such, but were the names of lunar months beginning with each new moon. According to Jonathan Carver in 1778, “Some nations among them reckon their years by moons, and make them consist of twelve synodical or lunar months, observing, when thirty moons have waned, to add a supernumerary one, which they term the lost moon; and then begin to count as before.” Carver gave the names of the lunar months (starting from the first after the March equinox) as Worm, Plants, Flowers, Hot, Buck, Sturgeon, Corn, Travelling, Beaver, Hunting, Cold, Snow. Carver’s account was reproduced verbatim in Events in Indian History (1841), but completely different lists were given by Eugene Vetromile (1856) and Peter Jones (1861).

In a book on Native American culture published in 1882, Richard Irving Dodge stated: There is a difference among authorities as to whether or not the moons themselves are named. Brown gives names for nine moons corresponding to months. Maximillian gives the names of twelve moons; and Belden, who lived many years among the Sioux, asserts that “the Indians compute their time very much as white men do, only they use moons instead of months to designate the seasons, each answering to some month in our calendar." Then follows a list of twelve moons with Indian and English names. While I cannot contradict so positive and minute a statement of one so thoroughly in a position to know, I must assert with equal positiveness that I have never met any wild Indians, of the Sioux or other Plains tribes, who had a permanent, common, conventional name for any moon. The looseness of Belden's general statement, that “Indians compute time like white people," when his only particularization of similarity is between the months and moons, is in itself sufficient to render the whole statement questionable.

My experience is that the Indian, in attempting to fix on a particular moon, will designate it by some natural and well-known phenomenon which culminates during that moon. But two Indians of the same tribe may fix on different designations ; and even the same Indian, on different occasions, may give different names to the same moon. Thus, an Indian of the middle Plains will to-day designate a spring moon as “the moon when corn is planted;" to-morrow, speaking of the same moon, he may call it "the moon when the buffalo comes." Moreover, though there are thirteen moons in our year, no observer has ever given an Indian name to the thirteenth. My opinion is, that if any of the wild tribes have given conventional names to twelve moons, it is not an indigenous idea, but borrowed from the whites.

Jonathan Carver's list of purportedly Native American month names was adopted in the 19th century by the Improved Order of Red Men, an all-white U.S. fraternal organization. They called the month of January "Cold moon", the rest being Snow, Worm, Plant, Flower, Hot, Buck, Sturgeon, Corn, Travelling, Beaver and Hunting moon. They numbered years from the time of Columbus's arrival in America.

In The American Boy's Book of Signs, Signals and Symbols (1918), Daniel Carter Beard wrote: “The Indians' Moons naturally vary in the different parts of the country, but by comparing them all and striking an average as near as may be, the moons are reduced to the following.” He then gave a list that had two names for each lunar month, again quite different from earlier lists that had been published.

The 1937 Maine Farmers' Almanac published a list of full moon names that it said "were named by our early English ancestors as follows":

Winter Moons: Moon after Yule, Wolf Moon, Lenten Moon Spring Moons: Egg Moon, Milk Moon, Flower Moon Summer Moons: Hay Moon, Grain Moon, Fruit Moon Fall Moons: Harvest Moon, Hunter's Moon, Moon before Yule

It also mentioned blue moon. These were considered in some quarters to be Native American full moon names, and some were adopted by colonial Americans. The Farmers' Almanac (since 1955 published in Maine, but not the same publication as the Maine Farmers' Almanac) continues to print such names.

Such names have gained currency in American folklore. They appeared in print more widely outside of the almanac tradition from the 1990s in popular publications about the Moon. Mysteries of the Moon by Patricia Haddock ("Great Mysteries Series", Greenhaven Press, 1992) gave an extensive list of such names along with the individual tribal groups they were supposedly associated with. Haddock supposes that certain "Colonial American" moon names were adopted from Algonquian languages (which were formerly spoken in the territory of New England), while others are based in European tradition (e.g. the Colonial American names for the May moon, "Milk Moon", "Mother's Moon", "Hare Moon" have no parallels in the supposed native names, while the name of November, "Beaver Moon" is supposedly based in an Algonquian language). Many other names have been reported.

These have passed into modern mythology, either as full-moon names, or as names for lunar months. Deanna J. Conway's Moon Magick: Myth & Magick, Crafts & Recipes, Rituals & Spells (1995) gave as headline names for the lunar months (from January): Wolf, Ice, Storm, Growing, Hare, Mead, Hay, Corn, Harvest, Blood, Snow, Cold. Conway also gave multiple alternative names for each month, e.g. the first lunar month after the winter solstice could be called the Wolf, Quiet, Snow, Cold, Chaste or Disting Moon, or the Moon of Little Winter. For the last lunar month Conway offered the names Cold, Oak or Wolf Moon, or Moon of Long Nights, Long Night's Moon, Aerra Geola (Month Before Yule), Wintermonat (Winter Month), Heilagmanoth (Holy Month), Big Winter Moon, Moon of Popping Trees. Conway did not cite specific sources for most of the names she listed, but some have gained wider currency as full-moon names, such as Pink Moon for a full moon in April, Long Night's Moon for the last in December and Ice Moon for the first full moon of January or February.

Hindu full moon festivals
In Hinduism, most festivals are celebrated on auspicious days. Many Hindu festivals are celebrated on days with a full moon night, called the purnima. Different parts of India celebrate the same festival with different names, as listed below:
 * 1) Chaitra Purnima – Gudi Padua, Ugadi, Hanuman Jayanti (15 April 2014)
 * 2) Vaishakha Purnima – Narasimha Jayanti, Buddha Jayanti (14 May 2014)
 * 3) Jyeshtha Purnima – Savitri Vrata, Vat Purnima (8 June 2014)
 * 4) Ashadha Purnima – Guru Purnima, Vyasa Purnima
 * 5) Shravana Purnima – Upanayana ceremony, Avani Avittam, Raksha Bandhan, Onam
 * 6) Bhadrapada Purnima – Start of Pitru Paksha, Madhu Purnima
 * 7) Ashvin Purnima – Sharad Purnima
 * 8) Kartika Purnima – Karthikai Deepam, Thrukkarthika
 * 9) Margashirsha Purnima – Thiruvathira, Dattatreya Jayanti
 * 10) Pushya Purnima – Thaipusam, Shakambhari Purnima
 * 11) Magha Purnima
 * 12) Phalguna Purnima – Holi

Lunar and lunisolar calendars

Most pre-modern calendars the world over were lunisolar, combining the solar year with the lunation by means of intercalary months. The Julian calendar abandoned this method in favour of a purely solar reckoning while conversely the 7th-century Islamic calendar opted for a purely lunar one.

A continuing lunisolar calendar is the Hebrew calendar. Evidence of this is noted in the dates of Passover and Easter in Judaism and Christianity, respectively. Passover falls on the full moon on 15 Nisan of the Hebrew calendar. The date of the Jewish Rosh Hashana and Sukkot festivals along with all other Jewish holidays are dependent on the dates of the new moons.

Intercalary months
In lunisolar calendars, an intercalary month occurs seven times in the 19 years of the Metonic cycle, or on average every 2.7 years (19/7). In the Hebrew calendar this is noted with a periodic extra month of Adar in the early spring.

title: Full moon


text:
Film format

A film format is a technical definition of a set of standard characteristics regarding image capture on photographic film for still images or film stock for filmmaking. It can also apply to projected film, either slides or movies. The primary characteristic of a film format is its size and shape.

In the case of motion picture film, the format sometimes includes audio parameters. Other characteristics usually include the film gauge, pulldown method, lens anamorphosis (or lack thereof), and film gate or projector aperture dimensions, all of which need to be defined for photography as well as projection, as they may differ.

Motion picture film formats

 * 35 mm movie film

Photographic film formats

 * 35mm film

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

title: Film format


text:
Faster-than-light

Faster-than-light (superluminal or supercausal) travel and communication are the conjectural propagation of matter or information faster than the speed of light ($c$). The special theory of relativity implies that only particles with zero rest mass (i.e., photons) may travel at the speed of light, and that nothing may travel faster.

Particles whose speed exceeds that of light (tachyons) have been hypothesized, but their existence would violate causality and would imply time travel. The scientific consensus is that they do not exist.

According to all observations and current scientific theories, matter travels at slower-than-light (subluminal) speed with respect to the locally distorted spacetime region. Speculative faster-than-light concepts include the Alcubierre drive, Krasnikov tubes, traversable wormholes, and quantum tunneling. Some of these proposals find loopholes around general relativity, such as by expanding or contracting space to make the object appear to be travelling greater than c. Such proposals are still widely believed to be impossible as they still violate current understandings of causality, and they all require fanciful mechanisms to work (such as requiring exotic matter).

Superluminal travel of non-information
In the context of this article, "faster-than-light" means the transmission of information or matter faster than c, a constant equal to the speed of light in vacuum, which is 299,792,458 m/s (by definition of the metre) or about 186,282.397 miles per second. This is not quite the same as traveling faster than light, since: Neither of these phenomena violates special relativity or creates problems with causality, and thus neither qualifies as faster-than-light as described here.
 * Some processes propagate faster than c, but cannot carry information (see examples in the sections immediately following).
 * In some materials where light travels at speed c/n (where n is the refractive index) other particles can travel faster than c/n (but still slower than c), leading to Cherenkov radiation (see phase velocity below).

In the following examples, certain influences may appear to travel faster than light, but they do not convey energy or information faster than light, so they do not violate special relativity.

Daily sky motion
For an earth-bound observer, objects in the sky complete one revolution around the Earth in one day. Proxima Centauri, the nearest star outside the Solar System, is about four and a half light-years away. In this frame of reference, in which Proxima Centauri is perceived to be moving in a circular trajectory with a radius of four light years, it could be described as having a speed many times greater than c as the rim speed of an object moving in a circle is a product of the radius and angular speed. It is also possible on a geostatic view, for objects such as comets to vary their speed from subluminal to superluminal and vice versa simply because the distance from the Earth varies. Comets may have orbits which take them out to more than 1000 AU. The circumference of a circle with a radius of 1000 AU is greater than one light day. In other words, a comet at such a distance is superluminal in a geostatic, and therefore non-inertial, frame.

Light spots and shadows
If a laser beam is swept across a distant object, the spot of laser light can easily be made to move across the object at a speed greater than c. Similarly, a shadow projected onto a distant object can be made to move across the object faster than c. In neither case does the light travel from the source to the object faster than c, nor does any information travel faster than light.

Closing speeds
The rate at which two objects in motion in a single frame of reference get closer together is called the mutual or closing speed. This may approach twice the speed of light, as in the case of two particles travelling at close to the speed of light in opposite directions with respect to the reference frame.

Imagine two fast-moving particles approaching each other from opposite sides of a particle accelerator of the collider type. The closing speed would be the rate at which the distance between the two particles is decreasing. From the point of view of an observer standing at rest relative to the accelerator, this rate will be slightly less than twice the speed of light.

Special relativity does not prohibit this. It tells us that it is wrong to use Galilean relativity to compute the velocity of one of the particles, as would be measured by an observer traveling alongside the other particle. That is, special relativity gives the correct velocity-addition formula for computing such relative velocity.

It is instructive to compute the relative velocity of particles moving at v and −v in accelerator frame, which corresponds to the closing speed of 2v > c. Expressing the speeds in units of c, β = v/c:
 * $$\beta_\text{rel} = \frac{\beta + \beta}{1 + \beta ^2} = \frac{2\beta}{1 + \beta^2} \leq 1.$$

Proper speeds
If a spaceship travels to a planet one light-year (as measured in the Earth's rest frame) away from Earth at high speed, the time taken to reach that planet could be less than one year as measured by the traveller's clock (although it will always be more than one year as measured by a clock on Earth). The value obtained by dividing the distance traveled, as determined in the Earth's frame, by the time taken, measured by the traveller's clock, is known as a proper speed or a proper velocity. There is no limit on the value of a proper speed as a proper speed does not represent a speed measured in a single inertial frame. A light signal that left the Earth at the same time as the traveller would always get to the destination before the traveller would.

Phase velocities above c
The phase velocity of an electromagnetic wave, when traveling through a medium, can routinely exceed c, the vacuum velocity of light. For example, this occurs in most glasses at X-ray frequencies. However, the phase velocity of a wave corresponds to the propagation speed of a theoretical single-frequency (purely monochromatic) component of the wave at that frequency. Such a wave component must be infinite in extent and of constant amplitude (otherwise it is not truly monochromatic), and so cannot convey any information. Thus a phase velocity above c does not imply the propagation of signals with a velocity above c.

Group velocities above c
The group velocity of a wave may also exceed c in some circumstances. In such cases, which typically at the same time involve rapid attenuation of the intensity, the maximum of the envelope of a pulse may travel with a velocity above c. However, even this situation does not imply the propagation of signals with a velocity above c, even though one may be tempted to associate pulse maxima with signals. The latter association has been shown to be misleading, because the information on the arrival of a pulse can be obtained before the pulse maximum arrives. For example, if some mechanism allows the full transmission of the leading part of a pulse while strongly attenuating the pulse maximum and everything behind (distortion), the pulse maximum is effectively shifted forward in time, while the information on the pulse does not come faster than c without this effect. However, group velocity can exceed c in some parts of a Gaussian beam in vacuum (without attenuation). The diffraction causes the peak of the pulse to propagate faster, while overall power does not.

Cosmic expansion
According to Hubble's law, the expansion of the universe causes distant galaxies to recede from us faster than the speed of light. However, the recession speed associated with Hubble's law, defined as the rate of increase in proper distance per interval of cosmological time, is not a velocity in a relativistic sense. Moreover, in general relativity, velocity is a local notion, and there is not even a unique definition for the relative velocity of a cosmologically distant object. Faster-than-light cosmological recession speeds are entirely a coordinate effect.

There are many galaxies visible in telescopes with redshift numbers of 1.4 or higher. All of these have cosmological recession speeds greater than the speed of light. Because the Hubble parameter is decreasing with time, there can actually be cases where a galaxy that is receding from us faster than light does manage to emit a signal which reaches us eventually.

However, because the expansion of the universe is accelerating, it is projected that most galaxies will eventually cross a type of cosmological event horizon where any light they emit past that point will never be able to reach us at any time in the infinite future, because the light never reaches a point where its "peculiar velocity" towards us exceeds the expansion velocity away from us (these two notions of velocity are also discussed in Comoving and proper distances). The current distance to this cosmological event horizon is about 16 billion light-years, meaning that a signal from an event happening at present would eventually be able to reach us in the future if the event was less than 16 billion light-years away, but the signal would never reach us if the event was more than 16 billion light-years away.

Astronomical observations
Apparent superluminal motion is observed in many radio galaxies, blazars, quasars, and recently also in microquasars. The effect was predicted before it was observed by Martin Rees and can be explained as an optical illusion caused by the object partly moving in the direction of the observer, when the speed calculations assume it does not. The phenomenon does not contradict the theory of special relativity. Corrected calculations show these objects have velocities close to the speed of light (relative to our reference frame). They are the first examples of large amounts of mass moving at close to the speed of light. Earth-bound laboratories have only been able to accelerate small numbers of elementary particles to such speeds.

Quantum mechanics
Certain phenomena in quantum mechanics, such as quantum entanglement, might give the superficial impression of allowing communication of information faster than light. According to the no-communication theorem these phenomena do not allow true communication; they only let two observers in different locations see the same system simultaneously, without any way of controlling what either sees. Wavefunction collapse can be viewed as an epiphenomenon of quantum decoherence, which in turn is nothing more than an effect of the underlying local time evolution of the wavefunction of a system and all of its environment. Since the underlying behavior does not violate local causality or allow FTL communication, it follows that neither does the additional effect of wavefunction collapse, whether real or apparent.

The uncertainty principle implies that individual photons may travel for short distances at speeds somewhat faster (or slower) than c, even in vacuum; this possibility must be taken into account when enumerating Feynman diagrams for a particle interaction. However, it was shown in 2011 that a single photon may not travel faster than c. In quantum mechanics, virtual particles may travel faster than light, and this phenomenon is related to the fact that static field effects (which are mediated by virtual particles in quantum terms) may travel faster than light (see section on static fields above). However, macroscopically these fluctuations average out, so that photons do travel in straight lines over long (i.e., non-quantum) distances, and they do travel at the speed of light on average. Therefore, this does not imply the possibility of superluminal information transmission.

There have been various reports in the popular press of experiments on faster-than-light transmission in optics — most often in the context of a kind of quantum tunnelling phenomenon. Usually, such reports deal with a phase velocity or group velocity faster than the vacuum velocity of light. However, as stated above, a superluminal phase velocity cannot be used for faster-than-light transmission of information

Hartman effect
The Hartman effect is the tunneling effect through a barrier where the tunneling time tends to a constant for large barriers. This could, for instance, be the gap between two prisms. When the prisms are in contact, the light passes straight through, but when there is a gap, the light is refracted. There is a non-zero probability that the photon will tunnel across the gap rather than follow the refracted path.

However, it has been claimed that the Hartman effect cannot actually be used to violate relativity by transmitting signals faster than c, also because the tunnelling time "should not be linked to a velocity since evanescent waves do not propagate". The evanescent waves in the Hartman effect are due to virtual particles and a non-propagating static field, as mentioned in the sections above for gravity and electromagnetism.

Casimir effect
In physics, the Casimir–Polder force is a physical force exerted between separate objects due to resonance of vacuum energy in the intervening space between the objects. This is sometimes described in terms of virtual particles interacting with the objects, owing to the mathematical form of one possible way of calculating the strength of the effect. Because the strength of the force falls off rapidly with distance, it is only measurable when the distance between the objects is extremely small. Because the effect is due to virtual particles mediating a static field effect, it is subject to the comments about static fields discussed above.

EPR paradox
The EPR paradox refers to a famous thought experiment of Albert Einstein, Boris Podolsky and Nathan Rosen that was realized experimentally for the first time by Alain Aspect in 1981 and 1982 in the Aspect experiment. In this experiment, the two measurements of an entangled state are correlated even when the measurements are distant from the source and each other. However, no information can be transmitted this way; the answer to whether or not the measurement actually affects the other quantum system comes down to which interpretation of quantum mechanics one subscribes to.

An experiment performed in 1997 by Nicolas Gisin has demonstrated quantum correlations between particles separated by over 10 kilometers. But as noted earlier, the non-local correlations seen in entanglement cannot actually be used to transmit classical information faster than light, so that relativistic causality is preserved. The situation is akin to sharing a synchronized coin flip, where the second person to flip their coin will always see the opposite of what the first person sees, but neither has any way of knowing whether they were the first or second flipper, without communicating classically. See No-communication theorem for further information. A 2008 quantum physics experiment also performed by Nicolas Gisin and his colleagues has determined that in any hypothetical non-local hidden-variable theory, the speed of the quantum non-local connection (what Einstein called "spooky action at a distance") is at least 10,000 times the speed of light.

Delayed choice quantum eraser
The delayed-choice quantum eraser is a version of the EPR paradox in which the observation (or not) of interference after the passage of a photon through a double slit experiment depends on the conditions of observation of a second photon entangled with the first. The characteristic of this experiment is that the observation of the second photon can take place at a later time than the observation of the first photon, which may give the impression that the measurement of the later photons "retroactively" determines whether the earlier photons show interference or not, although the interference pattern can only be seen by correlating the measurements of both members of every pair and so it cannot be observed until both photons have been measured, ensuring that an experimenter watching only the photons going through the slit does not obtain information about the other photons in an faster-than-light or backwards-in-time manner.

Superluminal communication
Faster-than-light communication is, according to relativity, equivalent to time travel. What we measure as the speed of light in vacuum (or near vacuum) is actually the fundamental physical constant c. This means that all inertial and, for the coordinate speed of light, non-inertial observers, regardless of their relative velocity, will always measure zero-mass particles such as photons traveling at c in vacuum. This result means that measurements of time and velocity in different frames are no longer related simply by constant shifts, but are instead related by Poincaré transformations. These transformations have important implications:
 * The relativistic momentum of a massive particle would increase with speed in such a way that at the speed of light an object would have infinite momentum.
 * To accelerate an object of non-zero rest mass to c would require infinite time with any finite acceleration, or infinite acceleration for a finite amount of time.
 * Either way, such acceleration requires infinite energy.
 * Some observers with sub-light relative motion will disagree about which occurs first of any two events that are separated by a space-like interval. In other words, any travel that is faster-than-light will be seen as traveling backwards in time in some other, equally valid, frames of reference, or need to assume the speculative hypothesis of possible Lorentz violations at a presently unobserved scale (for instance the Planck scale). Therefore, any theory which permits "true" FTL also has to cope with time travel and all its associated paradoxes, or else to assume the Lorentz invariance to be a symmetry of thermodynamical statistical nature (hence a symmetry broken at some presently unobserved scale).
 * In special relativity the coordinate speed of light is only guaranteed to be c in an inertial frame; in a non-inertial frame the coordinate speed may be different from c. In general relativity no coordinate system on a large region of curved spacetime is "inertial", so it is permissible to use a global coordinate system where objects travel faster than c, but in the local neighborhood of any point in curved spacetime we can define a "local inertial frame" and the local speed of light will be c in this frame, with massive objects moving through this local neighborhood always having a speed less than c in the local inertial frame.

Casimir vacuum and quantum tunnelling
Special relativity postulates that the speed of light in vacuum is invariant in inertial frames. That is, it will be the same from any frame of reference moving at a constant speed. The equations do not specify any particular value for the speed of light, which is an experimentally determined quantity for a fixed unit of length. Since 1983, the SI unit of length (the meter) has been defined using the speed of light.

The experimental determination has been made in vacuum. However, the vacuum we know is not the only possible vacuum which can exist. The vacuum has energy associated with it, called simply the vacuum energy, which could perhaps be altered in certain cases. When vacuum energy is lowered, light itself has been predicted to go faster than the standard value c. This is known as the Scharnhorst effect. Such a vacuum can be produced by bringing two perfectly smooth metal plates together at near atomic diameter spacing. It is called a Casimir vacuum. Calculations imply that light will go faster in such a vacuum by a minuscule amount: a photon traveling between two plates that are 1 micrometer apart would increase the photon's speed by only about one part in 1036. Accordingly, there has as yet been no experimental verification of the prediction. A recent analysis argued that the Scharnhorst effect cannot be used to send information backwards in time with a single set of plates since the plates' rest frame would define a "preferred frame" for FTL signaling. However, with multiple pairs of plates in motion relative to one another the authors noted that they had no arguments that could "guarantee the total absence of causality violations", and invoked Hawking's speculative chronology protection conjecture which suggests that feedback loops of virtual particles would create "uncontrollable singularities in the renormalized quantum stress-energy" on the boundary of any potential time machine, and thus would require a theory of quantum gravity to fully analyze. Other authors argue that Scharnhorst's original analysis, which seemed to show the possibility of faster-than-c signals, involved approximations which may be incorrect, so that it is not clear whether this effect could actually increase signal speed at all.

It was later claimed by Eckle et al. that particle tunneling does indeed occur in zero real time. Their tests involved tunneling electrons, where the group argued a relativistic prediction for tunneling time should be 500–600 attoseconds (an attosecond is one quintillionth (10−18) of a second). All that could be measured was 24 attoseconds, which is the limit of the test accuracy. Again, though, other physicists believe that tunneling experiments in which particles appear to spend anomalously short times inside the barrier are in fact fully compatible with relativity, although there is disagreement about whether the explanation involves reshaping of the wave packet or other effects.

Give up (absolute) relativity
Because of the strong empirical support for special relativity, any modifications to it must necessarily be quite subtle and difficult to measure. The best-known attempt is doubly special relativity, which posits that the Planck length is also the same in all reference frames, and is associated with the work of Giovanni Amelino-Camelia and João Magueijo. There are speculative theories that claim inertia is produced by the combined mass of the universe (e.g., Mach's principle), which implies that the rest frame of the universe might be preferred by conventional measurements of natural law. If confirmed, this would imply special relativity is an approximation to a more general theory, but since the relevant comparison would (by definition) be outside the observable universe, it is difficult to imagine (much less construct) experiments to test this hypothesis. Despite this difficulty, such experiments have been proposed.

Spacetime distortion
Although the theory of special relativity forbids objects to have a relative velocity greater than light speed, and general relativity reduces to special relativity in a local sense (in small regions of spacetime where curvature is negligible), general relativity does allow the space between distant objects to expand in such a way that they have a "recession velocity" which exceeds the speed of light, and it is thought that galaxies which are at a distance of more than about 14 billion light-years from us today have a recession velocity which is faster than light. Miguel Alcubierre theorized that it would be possible to create a warp drive, in which a ship would be enclosed in a "warp bubble" where the space at the front of the bubble is rapidly contracting and the space at the back is rapidly expanding, with the result that the bubble can reach a distant destination much faster than a light beam moving outside the bubble, but without objects inside the bubble locally traveling faster than light. However, several objections raised against the Alcubierre drive appear to rule out the possibility of actually using it in any practical fashion. Another possibility predicted by general relativity is the traversable wormhole, which could create a shortcut between arbitrarily distant points in space. As with the Alcubierre drive, travelers moving through the wormhole would not locally move faster than light travelling through the wormhole alongside them, but they would be able to reach their destination (and return to their starting location) faster than light traveling outside the wormhole.

Gerald Cleaver and Richard Obousy, a professor and student of Baylor University, theorized that manipulating the extra spatial dimensions of string theory around a spaceship with an extremely large amount of energy would create a "bubble" that could cause the ship to travel faster than the speed of light. To create this bubble, the physicists believe manipulating the 10th spatial dimension would alter the dark energy in three large spatial dimensions: height, width and length. Cleaver said positive dark energy is currently responsible for speeding up the expansion rate of our universe as time moves on.

Lorentz symmetry violation
The possibility that Lorentz symmetry may be violated has been seriously considered in the last two decades, particularly after the development of a realistic effective field theory that describes this possible violation, the so-called Standard-Model Extension. This general framework has allowed experimental searches by ultra-high energy cosmic-ray experiments and a wide variety of experiments in gravity, electrons, protons, neutrons, neutrinos, mesons, and photons. The breaking of rotation and boost invariance causes direction dependence in the theory as well as unconventional energy dependence that introduces novel effects, including Lorentz-violating neutrino oscillations and modifications to the dispersion relations of different particle species, which naturally could make particles move faster than light.

In some models of broken Lorentz symmetry, it is postulated that the symmetry is still built into the most fundamental laws of physics, but that spontaneous symmetry breaking of Lorentz invariance shortly after the Big Bang could have left a "relic field" throughout the universe which causes particles to behave differently depending on their velocity relative to the field; however, there are also some models where Lorentz symmetry is broken in a more fundamental way. If Lorentz symmetry can cease to be a fundamental symmetry at the Planck scale or at some other fundamental scale, it is conceivable that particles with a critical speed different from the speed of light be the ultimate constituents of matter.

In current models of Lorentz symmetry violation, the phenomenological parameters are expected to be energy-dependent. Therefore, as widely recognized, existing low-energy bounds cannot be applied to high-energy phenomena; however, many searches for Lorentz violation at high energies have been carried out using the Standard-Model Extension. Lorentz symmetry violation is expected to become stronger as one gets closer to the fundamental scale.

Superfluid theories of physical vacuum
In this approach, the physical vacuum is viewed as a quantum superfluid which is essentially non-relativistic, whereas Lorentz symmetry is not an exact symmetry of nature but rather the approximate description valid only for the small fluctuations of the superfluid background. Within the framework of the approach, a theory was proposed in which the physical vacuum is conjectured to be a quantum Bose liquid whose ground-state wavefunction is described by the logarithmic Schrödinger equation. It was shown that the relativistic gravitational interaction arises as the small-amplitude collective excitation mode whereas relativistic elementary particles can be described by the particle-like modes in the limit of low momenta. The important fact is that at very high velocities the behavior of the particle-like modes becomes distinct from the relativistic one – they can reach the speed of light limit at finite energy; also, faster-than-light propagation is possible without requiring moving objects to have imaginary mass.

MINOS experiment
In 2007 the MINOS collaboration reported results measuring the flight-time of 3 GeV neutrinos yielding a speed exceeding that of light by 1.8-sigma significance. However, those measurements were considered to be statistically consistent with neutrinos traveling at the speed of light. After the detectors for the project were upgraded in 2012, MINOS corrected their initial result and found agreement with the speed of light. Further measurements are going to be conducted.

OPERA neutrino anomaly
On September 22, 2011, a preprint from the OPERA Collaboration indicated detection of 17 and 28 GeV muon neutrinos, sent 730 kilometers (454 miles) from CERN near Geneva, Switzerland to the Gran Sasso National Laboratory in Italy, traveling faster than light by a relative amount of $2.48$ (approximately 1 in 40,000), a statistic with 6.0-sigma significance. On 17 November 2011, a second follow-up experiment by OPERA scientists confirmed their initial results. However, scientists were skeptical about the results of these experiments, the significance of which was disputed. In March 2012, the ICARUS collaboration failed to reproduce the OPERA results with their equipment, detecting neutrino travel time from CERN to the Gran Sasso National Laboratory indistinguishable from the speed of light. Later the OPERA team reported two flaws in their equipment set-up that had caused errors far outside their original confidence interval: a fiber-optic cable attached improperly, which caused the apparently faster-than-light measurements, and a clock oscillator ticking too fast.

Tachyons
In special relativity, it is impossible to accelerate an object the speed of light, or for a massive object to move  the speed of light. However, it might be possible for an object to exist which moves faster than light. The hypothetical elementary particles with this property are called tachyons or tachyonic particles. Attempts to quantize them failed to produce faster-than-light particles, and instead illustrated that their presence leads to an instability.

Various theorists have suggested that the neutrino might have a tachyonic nature,   while others have disputed the possibility.

General relativity
General relativity was developed after special relativity to include concepts like gravity. It maintains the principle that no object can accelerate to the speed of light in the reference frame of any coincident observer. However, it permits distortions in spacetime that allow an object to move faster than light from the point of view of a distant observer. One such distortion is the Alcubierre drive, which can be thought of as producing a ripple in spacetime that carries an object along with it. Another possible system is the wormhole, which connects two distant locations as though by a shortcut. Both distortions would need to create a very strong curvature in a highly localized region of space-time and their gravity fields would be immense. To counteract the unstable nature, and prevent the distortions from collapsing under their own 'weight', one would need to introduce hypothetical exotic matter or negative energy.

General relativity also recognizes that any means of faster-than-light travel could also be used for time travel. This raises problems with causality. Many physicists believe that the above phenomena are impossible and that future theories of gravity will prohibit them. One theory states that stable wormholes are possible, but that any attempt to use a network of wormholes to violate causality would result in their decay. In string theory, Eric G. Gimon and Petr Hořava have argued that in a supersymmetric five-dimensional Gödel universe, quantum corrections to general relativity effectively cut off regions of spacetime with causality-violating closed timelike curves. In particular, in the quantum theory a smeared supertube is present that cuts the spacetime in such a way that, although in the full spacetime a closed timelike curve passed through every point, no complete curves exist on the interior region bounded by the tube.

In fiction and popular culture
FTL travel is a common plot device in science fiction.

title: Faster-than-light


text:
FTL

FTL may stand for:

Science and technology

 * Faster-than-light communication and travel
 * Ferritin light chain, encoded by the FTL gene
 * Flash Translation Layer
 * Foot-lambert ft-L, a measure of luminance
 * Olympus FTL, a camera
 * FreeMarker template language

Games

 * Faster Than Light (software publisher), a British video game publisher
 * FTL: Faster Than Light, a video game
 * FTL Games, an American video game developer

Other uses

 * Fort Lauderdale, Florida, United States
 * Fort Lauderdale station, Amtrak code FTL
 * Freedom to Learn, in Michigan, United States
 * Fruit of the Loom, an American clothing manufacturer
 * Full truck load

title: FTL


text:
Talk:Flag

National Flags
This section states: ''The flag of the Netherlands is the oldest tricolour. Its three colours of red, white and blue go back to Charlemagne's time, the 9th century. The coastal region of what today is the Netherlands was then known for its cloth in these colours.'' The flag of the Netherlands is the oldest tricolour in continuous use, but tricolour flags are a relative recent invention, and it is highly doubtful made in the 9th century. I wonder what is the source of such claim.

Propose deletion within 14 days
I am proposing to delete the section on Similar Flags in its current format if noone offers a thorough defence as to why it does not deserve to be called Original Research. It firstly serves no analytical purpose and is potentially offensive to whichever nations are being bundled together. Secondly it is not based on any sources. None are cited. There is not verifiable research. The very idea to begin with is flawed because it apparently was born on Wikipedia. It exists in the mind of the person who decided each set. I could dispute each and every one by simply choosing a different set of characteristics to declare salient. I could say the Flag of Singapore ought instead to be grouped with those of Turkey and Tunisia because of red and white crescent and stars. So how do we judge that? Which are the defining characteristics, who says, and why? Why bother in the first place? Is this a major part of State Diplomacy? Does the UN arrange the Flags in this way? Indeed, why not start articles comparing anything and everything according to how any editor might choose on a whim, and say, "Similar books" and then categorize them according to the picture on the front cover of any arbitrary edition, and say, both these books have a picture of a man, or including the color orange, or does not feature a mosque, therefore is similar ?

So within 14 days if there is no reason it is not Original Research, and I mean, unless we get a verifiable and reliable source, I will delete. Eugene-elgato (talk) 17:28, 28 October 2010 (UTC)

 * OMG. I've just seen the section you mean. Well, all I can say is your patience and measured approach are to be applauded. The section is pointless WP:OR, adds nothing to the article, and deserves to go sooner rather than later. TFOWR 17:34, 28 October 2010 (UTC)
 * Thanks you very much. In fact, I'm almost glad it is there for now because finally I can see others who recognize it as almost a textbook example of what constitutes WP:OR. But let's see could be someone does located some university department somewhere that has justified some scheme to compare Flags outside the UN HQ in NY for the purposes of optimal ease on the human eye when scanning through them.Eugene-elgato (talk) 17:59, 28 October 2010 (UTC)

 * No Original Research

"Wikipedia does not publish original research or original thought. This includes unpublished facts, arguments, speculation, and ideas; and any unpublished analysis or synthesis of published material that serves to advance a position." '''[U]npublished...speculation[]and ideas"80.40.144.68 (talk) 07:11, 29 October 2010 (UTC)
 * Yes, it's precisely the unpublished speculation and ideas that worries me the most here; it is pure speculation and there is neither solid theory or justification underpinning each of these groupings, nor any point to it to begin with. Personally according to my taste I would have all the flags that feature th Star of David i.e. Morroco, State of Israel, Ethiopia, and Somalia. At least then it's not just any star but a particular star. But even then, what's the point; it would piss of the Ethiopians and the Somalis who have been at war. They all have their own reasons for adopting that Star anyway. On the other hand someone else would keep Somalia and Israel in the same group because they're both blue and white but send Ethiopia over to the flags that have the African tricolor.

Anyway, enough ranting :P Eugene-elgato (talk) 11:37, 29 October 2010 (UTC)
 * Gallery of flags by design is on the Wikimedia Commons. This has some structure to it and is featured as the link on similar flags on the flag template. This should be referred to if anyone wants to keep anything under that section.Eugene-elgato (talk) 09:42, 7 November 2010 (UTC)
 * I got rid of them now. I forgot to add an Edit Summary when I did it. No offence to all the editors before me who make the effort and amend more sets of similar flags; but I did warn precisely two weeks ago and have had the backing of two editors and no-one came to the defence of similar flags as not Original Research. As can be seen in the edit history for the article there are spurious reasons like "they're not very similar" even though evidently someone did think them dimilar at one stage. The link to the gallery has got some more objective classifications. Apart from anything else though, the similar flags section was making the Article kind of longEugene-elgato (talk) 18:22, 12 November 2010 (UTC)

No USA flag?
Why isn't there a US flag, or EU flag? —Preceding unsigned comment added by 76.181.114.227 (talk) 20:26, 26 November 2010 (UTC)
 * I don't think the article needs to include every flag. We don't have city flags for example. Saturdayseven (talk) 15:16, 18 March 2011 (UTC)

bayrak: http://www.bayrak.biz.tr —Preceding unsigned comment added by 217.31.248.13 (talk) 10:17, 15 December 2010 (UTC)

Largest flags
I have added a section on largest flags flown restored from a previous edit. Zarcadia (talk) 18:56, 5 January 2011 (UTC)

Is a flag primarily a piece of cloth?
Or is a flag the symbol that is placed on the cloth? I think the into might need to be changed to reflect this distinction but we'll need to find sources. Saturdayseven (talk) 13:28, 15 March 2011 (UTC)
 * Actually the article's defenition of "flag" is correct. I found this source from merriam-webster.com defining a flag: "a usually rectangular piece of fabric of distinctive design that is used as a symbol (as of a nation), as a signaling device, or as a decoration"Saturdayseven (talk) 13:38, 15 March 2011 (UTC)
 * Added this reference to the article. Saturdayseven (talk) 13:48, 15 March 2011 (UTC)
 * And both defenitions of flag are in the intro because the article also states: The term flag is also used to refer to the graphic design employed by a flag, or to its depiction in another medium. Saturdayseven (talk) 13:49, 15 March 2011 (UTC)

Inspiration from Greece?
The Greek flag is included in the list of flags that have served as inspiration for other flags. But why? The section does not mention which flags were inspired by it. --Thathánka Íyotake (talk) 19:47, 30 October 2011 (UTC)
 * I've deleted it, it was rubbish, the Greek flag was inspired by the US flag... no countries mentioned so not of any use in this article. Dqfn13 (talk) 10:08, 31 October 2011 (UTC)

Roman Army Dragon standard
It might be worth mentioning the work done by the archaeologists of TimeTeam in the UK, making a Dragon banner and solving the roaring sound, caused by Chinese wind-chime drums of sorts secured to the staff, which also explained the odd blobs shown there on several of the source carvings. — Preceding unsigned comment added by 188.28.75.66 (talk) 08:57, 18 May 2012 (UTC)

Taxonomy
I think you can go further, as there are clear heraldic differentiations between a standard, a banner, a banneret, a pennon and some other forms which elude me for the moment. If you treat vertical flags in a National context, then you should also certainly mention the Japanese, and, IIRC, Chinese/Mongolians, although I may be corrected on that. It might perhaps be better to remove the national references or relegate them to links to the Nations concerned.

Under flag language, you might also mention the UK's practice of inverting the Union Flag as a covert warning.

You should also expand on the stub reference in the introduction to military flags, above and beyond the use of semaphore. For starters, the British Army considers its colours as the identity of the unit, with the exception of the artillery, whose colours are its cannon, in a direct descent from the Roman Eagles. This is why the Colour is always saluted. Similarly, the Royal Navy's colours carried at the stem are always saluted on joining or leaving the ship, and an Admiral also hoists his own colours, depending on his rank as Vice-Admiral, Rear-Admiral, Admiral or Admiral of the Fleet, and indeed in Napoleonic times, indicative of the Division he is part of as well. A further Naval flag worth mentioning is the Decommissioning pennon, probably the longest flag in existence: I recall the Ark Royal aircraft carrier coming into Portsmouth after years at sea in the 1960s, it's siging-off pennon was several times the not inconsiderable length of the ship! — Preceding unsigned comment added by 188.28.75.66 (talk) 09:17, 18 May 2012 (UTC)

Flag on the Moon
I feel like there should be a picture of the flag set up on the moon by the Apollo 11 astronauts. If for no other reason than it is a striking photo and was a giant leap for all flag-kind. That flag boldly went where no other flag had gone before. That flag is a symbol of human progress.

174.56.122.45 (talk) 05:10, 20 September 2015 (UTC)

 * I don't disagree, can you think of a good caption? I was going to go for something along the lines of "Flags are often planted to claim victory over something, or as a symbol to lay claim on a new place", but that's taken by the second image (of Jaan Künnap waving the Estonian flag on Lenin Peak). --BurritoBazooka (talk) 09:48, 20 September 2015 (UTC)

What is the point of the currently-uncited language "attempt to emulate the rainbow flag's success"?
Regarding the 'In politics' section: "an attempt to emulate the rainbow flag's success" seems glib, spinny, and it's unclear what's being said. Without clear citation of the individual claims... ... this comes off as an insertion of someone's personal opinions about the relative value-however-defined of various pride flags. If anyone can demonstrate the veracity of any or all of these claims, and restructure the language so that the claims being made are more plainly stated, I invite them to do so; else, seems to me the language is entirely unnecessary. Mvseaver (talk) 15:30, 13 December 2016 (UTC)
 * 1) The bi and trans flags were closely emulative of the rainbow flag versus, say, expansions on the generalizable/generalized concept of community pride flags (see "emulate the rainbow flag's success").
 * 2) The bi and trans flags were intended by their creators to be 'as successful' as the rainbow flag (see "emulate the rainbow flag's success"), and- by the way- the success metric here is unclear and frankly suspect.
 * 3) The bi and trans flags were 'less successful' or 'it's too soon to tell' about their success relative to the rainbow flag- which remains an oddly-motivated comparison to include, and a hard one to evaluate (see "an attempt," implying some sort of question about the attempt's success); this claim seems entirely unnecessary, although I'm prepared to be convinced otherwise.

 * It's uncited, and unnecessary. They're plainly derivatives. With a reliable source (?) more detailed claims might be useful at the Rainbow flag article; but not here. This is a general article on the topic. Or at least that's what it's supposed to be. Not one of our better articles. Anyhow, I've removed the claim. Haploidavey (talk) 15:51, 13 December 2016 (UTC)

Original research
I removed the section "Similar flags" with the edit summary Remove highly subjective original research. This was reverted with the edit summary ''unsatisfactorily explained removal of content. Take it to talk page.'' I am not sure what exactly is unsatisfactory about my explanation. My explanation has two parts: 1) "highly subjective" should be quite obvious. Some of the "similarities" are actually extremely far-fetched. 2) "original research" is also quite clear. There were no reliable sources covering the selection. (Since then, some sources have been added. They are, however, not much more than blogs, they do not cite any reliable sources, and they are quite clearly just other subjective selections.)

The section was started nine days ago and has up to my removal been edited by one single IP editor, with one single exception (another IP, one edit), so there is no long-standing consensus for the section. On the contrary: As the top section of this talk page shows, a similar section was removed by consensus in 2010. The standing consensus is thus not to have a "Similar flags" section. In order to re-establish a section removed by consensus, a new consensus must be built first. --T*U (talk) 18:00, 17 April 2017 (UTC)

 * Just to note my support for the removal. Wikipedia article content should be supported by reliable sources (in this case, vexillologists), not blogs or amateur websites, nor personal interpretations. Haploidavey (talk) 19:42, 17 April 2017 (UTC)
 * What part of Encyclopædia Britannica did you fail to grasp? The other sources are make weight, but don't detract from these other citations.  Throwing around WP:OR without reason is not helpful.  7&6=thirteen (☎) 13:26, 18 April 2017 (UTC)
 * Sorry, didn't mean to imply my support for removal of any well-supported material, nor a section based on the same. Haploidavey (talk) 15:14, 18 April 2017 (UTC)
 * The link from EB is not an encyclopedic article. It is a list article where "Britannica editors share their opinions, insightful commentary and fun facts on a variety of topics of personal interest", in the web cite's own words. It has thus no more weight than any of the other subjective sources. Also: What you seem not to grasp, is the Wiki principle of consensus. The current consensus (see above) is not to have such section. Instead of trying to edit war in the section, you should try to create a new consensus in the talk page. Please self revert your last edit, and take part in the discussion instead per WP:BRD. --T*U (talk) 15:19, 18 April 2017 (UTC)
 * You don't seem to grasp that I put in four (4) separate sources.

 * If the consensus is that these sources are insufficient, than I will certainly abide. But you need to grasp that articles evolve.  Better and more sources change the dynamic. There is no "Edit war" here that I have seen.  Best regards.  7&6=thirteen (☎) 00:37, 19 April 2017 (UTC)
 * 1) Not one of the so-called sources can be regarded as reliable sources as described here. They are just subjective lists of what their creators perceive as similar. Exactly like the current section here.
 * 2) I have counted 154 flags in the current "Similar flags" section. The so-called sources taken together cover less then half of them, most of which are not even commented on, just listed.
 * You could, of course, start by removing all the listed flags that are not covered by the so-called sources. But imho that is just a waste of time. I will soon start a RfC to get a wider input. Regards! --T*U (talk) 06:56, 19 April 2017 (UTC)

RFC is good idea. 7&6=thirteen (☎) 13:51, 19 April 2017 (UTC)

RfC about section "Similar flags"
A newly created section "Similar flags" consists of a short introductory text and a gallery of 150+ flags grouped by alleged similarity. Should the section be kept or deleted? T*U (talk) 16:25, 19 April 2017 (UTC)

Survey
to reply to me 15:19, 10 May 2017 (UTC)
 * Delete as highly subjective original research. This is just a gallery of flags that the creator of the section finds similar. Originally without any sources, some have been added later. They are all the same type of image galleries of flags perceived as similar by the list creators. Such subjective lists do not qualify as reliable sources. It should also be noted that a similar "Similar flags" section with 100+ flags was removed by consensus in November 2010. --T*U (talk) 16:25, 19 April 2017 (UTC)
 * Delete per above. Vaselineeeeeeee★★★ 16:57, 19 April 2017 (UTC)
 * Keep.. My Opinion: I think the section is useful; the Encyclopedia Britannica source is valid. I personally see similarities in the flags, similar per color shapes, placement and objects on the flags, so I think others would also.  It would be interesting to group the flags better, and then  explain why groups of flags are similar, for example a common history.  Per WP:Preserve keep and add citation needed tags in the places where sources are needed. If no sources can be found after x months stating some flag grooups are similar then delete the group flags.  I think similarities can be subjective and need to be sourced and explained.  But as WP is a work in progress, keep and source.CuriousMind01 (talk) 13:06, 20 April 2017 (UTC)
 * Valid points raised by CuriousMind. I wouldn't be opposed to it if we can delete the large number of "similar" flags that aren't sourced, and limit them only to sourced groupings that have some sort of historical explanation as to why the flags are similar, not just because they may "look similar" to some people. That should be the only grounds for inclusion. Vaselineeeeeeee★★★ 13:48, 20 April 2017 (UTC)
 * The link from EB is not an encyclopedic article. It is a list article where "Britannica editors share their opinions, insightful commentary and fun facts on a variety of topics of personal interest", in the web cite's own words. It is therefore just the subjective opinion of the list creator and has no value as a reliable source, just like the other sources. --T*U (talk) 13:50, 20 April 2017 (UTC)
 * T*U My opinion: the EB article is a valuable reliable source, written by a named person, who was a senior editor, and the article has valid facts, and meets the criteria for a reliable source.CuriousMind01 (talk) 15:31, 20 April 2017 (UTC)
 * Keep per above. This whole RFC effort proves that nobody cares much what we do.  5 million articles and we get overlooked.  Oh well.  7&6=thirteen (☎) 15:57, 21 April 2017 (UTC)
 * Yeah, it is a rather meagre attendance so far. This being the main article in the area, one should think more people were interested. Well, let's wait and see if more editors turn up with their thoughts. --T*U (talk) 12:57, 22 April 2017 (UTC)
 * T*U We gave a party and nobody came.  Or all dressed up and no place to go.  7&6=thirteen (☎) 13:30, 22 April 2017 (UTC)
 * Delete, unnecessarily large gallery (host it on Commons?). Jc86035 (talk) Use {{re|Jc86035}}

Threaded discussion
I am not against having a section about flag similarities. But the procedure proposed by is not the way to go about it. Grouping the flags first and then looking for sources is to start in the wrong end. First we would need to agree on what flags to group and by which criteria, and that would in reality require sources. Also, deliberately entering content tagged with and then waiting for months is hardly admissible per WP: Verifiability. Note that WP:Preserve states that content ("facts or ideas") should be kept "if they meet the three article content retention policies", i.e. WP:NPOV, WP:VER and WP:NOR. I agree with about deleting the large number of "similar" flags that aren't sourced, and include only sourced groupings that have some sort of historical explanation as to why the flags are similar. That might include flags in pan-African colours, flags in pan-Slavic colours, flags with Nordic cross, all of which presumably possible to source. Other examples are known relations like US–Liberia and Switzerland–Red cross. Then we move away from subjective "I think these flags look similar" to more objective "these flags are similar because they are related". But then maybe the section should be titled "Related flags", not "Similar flags". --T*U (talk) 12:57, 22 April 2017 (UTC)
 * Adapt: Best start from scratch. Adding or retaining unsourced content, or adding content then tagging for sources is certainly not the way to go; adding sourced groupings that have some sort of historical explanation as to why the flags are similar is sound reasoning, and conforms to policy. "Similarity" is something perceived; and per the very earliest discussions on the matter (see top page), "This one looks rather like that one, according to X sources - but so what?". "Relatedness" requires an historically informed, explanatory, sourced narrative. Haploidavey (talk) 13:16, 22 April 2017 (UTC)
 * This might be a way to do it. Thanks for the suggestions.  7&6=thirteen (☎) 13:31, 22 April 2017 (UTC)
 * Yes, related, not similar; good wording. Vaselineeeeeeee★★★ 16:47, 22 April 2017 (UTC)
 * Agree with relatedness with sources as good criteria for grouping. Looking at the section, it makes sense to have some of these together—the Union Jack flags, for example—whereas the Flag of Greenland probably has a closer relationship with the Flag of Denmark than with the Flag of Singapore. As it stands the section looks pretty reasonable at first glance, but there would be plenty of other ways to organize it that would look reasonable, based on shape and color. groupuscule (talk) 21:57, 24 April 2017 (UTC)

 * My opinion: WP:Preserve full quote is: "Likewise, as long as any of the facts or ideas added to an article would belong in the "finished" article, they should be retained if they meet the three article content retention policies: Neutral point of view (which does not mean no point of view), Verifiability and No original research."

 * Which to me means, if editors think the content belongs in the "finished" flag article, then tag citation needed.  I don't think the Flag article is a "finished" article, and so WP:PReserve applies, and a similar flags section belongs in the article.  I think historical groupings apply, example the Nordic Cross flags, and the similar flags noted in the Enc. Brit. article apply here too.

 * The RFC was written as a keep or delete the section, like an all or none approach, but I think keep and fix is a better approach here. Tag what needs sourcing, and after x time, delete what can't be sourced. Some groups may not have a common history, but are interesting to me to note similarities as done in the Enc Brit article.CuriousMind01 (talk) 12:16, 29 April 2017 (UTC)
 * Just a comment about WP:Preserve. If the facts or ideas belong in the "finished article", they should be retained if they meet the three article content retention policies. One of these policies is Verifiability, which means that sourcing is needed. If tagging with "citation needed" is needed, it does not meet the policy of Verifiability, so WP:Preserve does not apply. --T*U (talk) 12:21, 16 May 2017 (UTC)

Similar flags again
It is now one month since the RfC was closed. During the month it was open and the month that since has expired, there has been exactly zero attempts to start the procedure defined in the closure statement: "to restrict them to rigorously sourced groupings that have some sort of strong logical explanation as to the similarities, rather than being based on some abstract qualities". Since the closure there has also been exactly zero suggestions for groupings to keep. In fact, there has been exactly zero edits to this talk page. I do not know how long "a reasonable span of time" is supposed to be, but it could soon be time to delete the whole section.

However, rather than deleting, I will try to make a start of a new section "Related flags" to replace the current section, taking examples from the RfC discussion. I hope the title will encourage people to add only groups that have more than a coincidental similarity.

There are many candidates for additional subsections. Here are some suggestions for which it should or could be possible to find sources:
 * Pan-African colours (note that the relevant article is unsourced)
 * South American flags based on the Flag of Gran Colombia
 * Central American flags based on the flag of the Federal Republic of Central America
 * Flags with Union Jack in the canton
 * Flags based on the flag of the Ottoman Empire with its crescent and star (note that not all crescent-and-star-flags will qualify)
 * Possible relationship between the flag of Texas and the flag of Chile
 * and so on...

I have at least made a start. Perhaps others will follow? --T*U (talk) 09:41, 21 June 2017 (UTC)

WP:verifiability add citation needed tag Reply
T*U The RFC text section is closed, so I responded here:

WP:Preserve applies because WP:Verifiability describes adding a citation needed tag as an interim step.

Regarding: ''CuriousMind01: Just a comment about WP:Preserve. If the facts or ideas belong in the "finished article", they should be retained if they meet the three article content retention policies. One of these policies is Verifiability, which means that sourcing is needed. If tagging with "citation needed" is needed, it does not meet the policy of Verifiability, so WP:Preserve does not apply. --T*U (talk) 12:21, 16 May 2017 (UTC) ''

T*U Please see WP:verifiability "In some cases, editors may object if you remove material without giving them time to provide references; consider adding a citation needed tag as an interim step.  CuriousMind01 (talk) 11:09, 29 June 2017 (UTC)
 * Forgive me if I am wrong, but I get the impression from your comment that you have not read the closing remarks of the RfC or my comment in the section above this one. The closing comment says nothing about citation needed-tagging, but requires "rigorously sourced groupings that have some sort of strong logical explanation as to the similarities". Failing that "within a reasonable span of time, the section shall be deleted". It can, of course, be discussed how lang "a reasonable span of time" is, but since no-one has even attempted to suggest "rigorously sourced groupings" during the month of the RfC and now soon one and a half month more, I think it is time to move on. As you will see, I have not only deleted the "Similar flags" section, but have also started a new section "Related flags", where "rigorously sourced groupings" can be presented and described, "sourced" being the key word. --T*U (talk) 20:03, 30 June 2017 (UTC)
 * T*U Sorry for not explaining, I was responding to your comment regarding WP Preserve, as an informational post, trying to explain how WP Preserve works, not to continue discussion post RFC. I did read the RFC closing statement and your comments and actions.  I have no objection to the updates you made to the article.  Thank you, CuriousMind01 (talk) 20:44, 30 June 2017 (UTC)
 * Fine, then! I hope someone takes me up on the challenge of expanding the "Related flags" section. And just for the record, I am not sure I agree with your interpretation of WP:Preserve, but that does not really matter now. Regards! --T*U (talk) 22:15, 1 July 2017 (UTC)

External links modified
Hello fellow Wikipedians,

I have just modified one external link on Flag. Please take a moment to review my edit. If you have any questions, or need the bot to ignore the links, or the page altogether, please visit this simple FaQ for additional information. I made the following changes:
 * Added tag to ftp://cenftp1.cenorm.be/PUBLIC/CWAs/e-Europe/ESR/cwa14094-00-2001-Jan.pdf
 * Added archive https://web.archive.org/web/20150403170745/http://www.sheboyganpress.com/article/20140525/SHE0101/305250197/High-flying-Up-time-Memorial-Day-Acuity-flag-world-s-tallest to http://www.sheboyganpress.com/article/20140525/SHE0101/305250197/High-flying-Up-time-Memorial-Day-Acuity-flag-world-s-tallest

When you have finished reviewing my changes, you may follow the instructions on the template below to fix any issues with the URLs.

Cheers.— InternetArchiveBot  (Report bug) 22:57, 1 October 2017 (UTC)

Merge most of section on national flags into section on related flags
Most of the section on national flags discusses how some national flags served as a model for other flags. This duplicates some of the information presented in the section on related flags, which has the specific purpose of describing those relationships. I therefore propose to merge such content into the section on related flags. Hamish Lawson (talk) 10:51, 12 November 2020 (UTC)

Raising the flag
In another article (Tripartite Convention) there is a red link for "flag-raising". "Flag raising ceremony" is a redirect to "Hoisting the flag". It would be nice if there was info at "Hoisting the flag" or in a separate section about the use of a flag raising or planting in claiming territory or formally acknowledging a change of government. As far as I can see there is no specific discussion of that here or elsewhere. If there is, I'd be happy to hear about it so that the link at "Tripartite Convention" can be properly directed. It seems to me that flag-raising is very often a crucial symbolic part of transfers of territory. Brianyoumans (talk) 19:50, 18 January 2021 (UTC)

Intro definition too broad; proposal of a new one
Here is the introduction:

 * A flag is a piece of fabric (most often rectangular or quadrilateral) with a distinctive design and colours. It is used as a symbol, a signalling device, or for decoration.

The first sentence is so broad as to be useless. A blanket, a curtain, a beach towel, a table cloth, a cape, a rug, a tapestry, a scarf, and so on, are all pieces of fabric that are usually quadrilateral and have distinctive designs and colors.

And to say that such a piece of fabric is used as a symbol, a signalling device, or for decoration doesn't help, either: Superman's cape is a symbol, a handkerchief waved in surrender is a signalling device, and a pillowcase can be used for decoration.

We can arrive at a more adequate definition is we consider for a moment who uses flags and for what purposes? Nations, branches of the military, and other organizations that represent some major social agent; or institutions and agencies or agents who regulate the activities of other agents or agencies through long-distance communication. So a better definition would run:

 * A flag is a usually quadrilateral strip of fabric so colored or colored and figured as to symbolize for and announce to the world, in public display so prominent as to admit no obscuring, the existence or presence of a supremely significant social entity, or to communicate provisionally authoritative or regulative states of affairs to all and sundry.

I think this captures all the essentials of paradigmatic flags; it is not necessary to try to frame a definition so that it covers all possible variations of a reality, regardless of their status, in a single sentence; decorative flags aren't paradigmatic flags, so there's no point in mentioning them in the same breath as the paradigmatic ones—that would be like trying to frame the definition of automobile so that it included toy cars.

What do you think? Wordwright (talk) 20:29, 6 November 2021 (UTC)
 * I think that the most notable and interesting meaning of "flag" is its use to announce the presence, ownership, or allegiance of a place or thing to some governmental, usually territorial, entity. It's a really hard concept to articulate clearly, though. As you say, it can also provide information on status, like quarantine flags or even just "this is open". It can represent people's faith, advocacy, or belief in something - a gay pride flag, or a religious flag, or a sports team (not far from a religion in some places...). And it can also by just a decoration, like a flag for a holiday or a season. Brianyoumans (talk) 15:26, 8 November 2021 (UTC)

Flag edit reference fix
Consider fixing references to this link manually. Refill2 messes up when attempting to fix references from this page. It tries to omit the use of looking at pages 33 and 41 separately. Perhaps whoever added this reference probably neglected to set page to 33 and 41 separately. I will not do this Refill2 edit. Qwertyxp2000 (talk | contribs) 09:50, 30 August 2022 (UTC)
 * Also, I would imagine that it might involve some use of citationing an online archive web source. Sadly, some of the pages on that article are archived but forced upon a paywall, so I can't manually fix it myself. Qwertyxp2000 (talk | contribs) 09:52, 30 August 2022 (UTC)

Notification of plans for significant changes
This is a very important article that's in desperate need of big updates. There are many significant problems regarding the accuracy and relevance of the content, and of the organization. This is much more than I can address in one edit, so I am working on creating a new version in my sandbox. You are welcome to contribute by suggesting changes here or at my talk page, or by editing my sandbox directly. (Also, please let me know if there's a different way I should be doing this. I'm still a pretty new editor.)  Not A  Witty Fish  21:17, 28 October 2022 (UTC)

Ahmad Chami Batch
Ahmad Chami Batch 101.191.211.247 (talk) 08:35, 1 June 2023 (UTC)

Vexilloid Ships
The text says "Ships with vexilloids were represented on predynastic Egyptian pottery c. 3500 BCE." before "In antiquity, field signs or standards that can be categorised as vexilloid or "flag-like" were used in warfare, which originated in ancient Egypt or Assyria." Shouldn't that order be switched? 104.187.66.104 (talk) 15:51, 16 June 2023 (UTC)

 * I'll switch for now. 104.187.66.104 (talk) 23:32, 19 June 2023 (UTC)
 * Never mind. I forgot it's protected. 104.187.66.104 (talk) 23:32, 19 June 2023 (UTC)

Vertical Flags
I feel like there should be an article depicting the vertical flag of each nation. The current section from my understanding is just depicting the fact that there are some flags meant to be vertical. I was surprised to find out something like this doesn't exist already. Perhaps, if not a page, it could be an addition to this page, showcasing some examples of the vertical flags of some nations? 7s3s (talk) 01:56, 26 May 2024 (UTC)

title: Talk:Flag