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Wikijunior:Solar System/Earth

Earth is the planet we live on. It is the only planet in the Solar System with liquid water on its surface. It is also the only planet we know to have life on it. Earth is also known as Terra.  Earth Facts
 * The Earth is the only planet we know to have life on it (such as ourselves.)
 * There is oxygen on Earth, and oxygen is necessary for life.
 * The Earth is the third planet from the Sun.
 * The Earth is the only planet we know that has liquid water on the surface, but scientists are trying to find others.
 * The Earth's axis is tilted which is why we have four different seasons.
 * The Earth is 4.6 billion years old.
 * The Hoba meteorite in Namibia is the biggest known meteorite to crash on Earth in one piece.

How big is the Earth?
The Earth is nearly 13,000 km wide. It's the largest terrestrial planet in the Solar System.

The Earth's mass is about 5,973,700,000,000,000,000,000,000 kg. That's a lot. But it is little compared with Jupiter (319 Earths) and tiny compared with the Sun (335,789 Earths) or other stars!

What is the Earth's surface like ?
The Earth's surface is made of rock. Most of it is underwater, but not all. Islands of rock rise up out of the water. The biggest islands are called continents, of which there are seven: North America, South America, Europe, Asia, Africa, Australia, and Antarctica. The largest bodies of water are called oceans, of which there are five: Pacific, Atlantic, Indian, Arctic and Antarctic or Southern.

The Earth's surface is made up of huge plates. They are like huge jigsaw pieces made of rock. These plates move very, very slowly, carrying the continents with them. They can rub beside each other, push against each other, or even move away from each other. If there are gaps between them, hot molten rock can rise up and make volcanoes. Where the plates rub or push against each other, earthquakes may happen. When two plates push each other's rock upwards, mountains are formed.

Earth has many kinds of environments. It is cold and icy in places like Antarctica. It is hot and dry in deserts like the Sahara in Africa and Death Valley in the United States. It is cold and dry in deserts like Siberia in Russia. Where it is warm and wet, rainforests grow.

Why is there life on Earth?
Wherever we have looked on Earth, we have found living things. They may be very small, like bacteria, but they are there. We have found bacteria where it is very cold, very hot, very deep, very high or very dark.

What all living things on Earth seem to need is liquid water. Wherever you can find some water, there are almost always living things there too, even if you can't see them. If we find liquid water somewhere else in the Solar System, scientists think we might find some living things there too. If we don't, there is always the rest of the universe to explore!

There is another possibility. All the living things we know need liquid water. But maybe somewhere else there are living things that don't need water. Perhaps we will need to learn how to recognize them.

What about the Earth's moon?
Earth has one moon we call... the Moon! Sometimes it is called by its name in Latin, Luna, so we don't get confused with other planets and their moons. The Moon has also been called Selene (pronounced "suh-LEE-nee") which is Greek for moon and was the name of the Greek moon goddess.

Recently we have also found some other objects that are said to go around the Earth. The largest one, called Cruithne (pronounced "cru-EE-nyuh"), is three miles wide. In fact, it orbits (goes around) the Sun in a way that makes it keep coming close to Earth.

There are various ideas about where the Moon came from (no-one was around to see it happen, after all), but the most widely held theory is that when Earth was young, a large body hit Earth and split off a section of the Earth that is now the Moon.

How long is a day on this planet?
A day on Earth is 24 hours long. That's daytime and night time. A 24 hour day is how long it takes the Earth to spin around once. On the half of the Earth that is facing the sun it is daytime and on the half of the Earth that is facing away from the sun it is nighttime.

The spin of the earth is also the reason why the sun appears to rise in the east and to set in the west. Although it looks like the sun is moving from the surface of the earth, it is really the surface of the earth that is moving. The reason we do not feel like we are spinning is because the earth is so big compared to the size of people.

Also, the Earth is tilted at about 23°, so there are times that the North or South pole is always facing or turned away from the sun. If you live at one of the poles of Earth it can be light or dark throughout the whole day!

How long is a year on this planet?
A year on Earth is about 365 and 1/4 days long. That's how long it takes the Earth to orbit the Sun once. Approximately every four years we have a leap year. A leap year contains an extra day in our calendar on February 29th in order to account for the 1/4 of a day left over each year.

What is the Earth made of?
When a planet is made of rock, we call its surface the crust. Below the Earth's crust is hot rock, some of which is molten. It is in a layer called the mantle. The hot molten rock is what comes out of volcanoes. It's then called lava.

Under the mantle is the core of the Earth. We think it is made from solid iron and nickel, surrounded by hot molten iron. The temperature there is very very hot!

The Earth's crust is very thin compared to the mantle and the core. But it is very thick to us. Nobody has drilled all the way through it yet. Even the deepest underground mines are far away from reaching its deepest base.

How much does the Earth's gravity pull on me?
It's easy to find your weight on Earth by using a scale. You have weight because the Earth's gravity pulls you towards its center. Normally, the ground or the floor get in the way, making you feel 'stuck' to them.

There are several kinds of scales:

1) Comparing of 2 masses (weights). You put the thing(s) you want to weigh on one pan (like some marbles), and then you put several "weights" on the other pan until the pointer shows that both pans have equal weights on them. Then you look at the pan with the known weights on it, and add them all up. The total is the mass of the thing(s) you want to weigh. 2) A spring balance usually has a hook on it, with a pan. You put the thing(s) you want to weigh on the pan, the spring is pulled, and the greater the weight, the further the spring is pulled. That distance, calibrated in pounds or kilogram (or whatever), is usually shown either on a dial or on a linear scale. 3) There are also electronic scales that give a properly calibrated reading—grocery stores, for example, use these.

NOTE: Gravity varies slightly depending on the location where you want to get the weight; spring balances and some electronic scales can, in theory, read slightly different weights at different places because of that, but usually in practice that difference is too small to be noticed. But, because the balance type of scales work differently from the spring or electronic types, they will always read the true, correct mass. They would even give the same mass on the Moon, where gravity is much less than on Earth.

Did you know? that Sir Isaac Newton was the first person to realize that the force pulling you down to the ground was the same force that keeps the planets going around the Sun? The story goes that he thought of this when he saw an apple fall from a tree.

Gravity is a very important force. As well as keeping you firmly stuck to the Earth, it keeps the Moon going round the Earth, The Earth going around the Sun and the Sun going around the center of the Milky Way galaxy. Gravity also makes stars and planets a nice round ball shape. In fact without gravity there wouldn't even be a Sun, Moon or Earth because the material that they are made of would just float away into space.

Who is it named after?

The word earth is used for both planet Earth and soil. Other names had been used for Earth such as Gaia, Tellus and Terra. Gaia is the Greek goddess (meaning Mother Earth) and Terra is the Roman name of the same goddess. Tellus is the Latin for "Earth", many scientific words dealing with Earth will be derived form Latin.

Next Topic: Moon

title: Wikijunior:Solar System/Earth


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Wikijunior:Solar System/Jupiter

Jupiter Facts:
 * Due to its magnetic field trapping particles from the Sun, Jupiter is surrounded by very powerful radiation belts which would kill anyone who entered them.
 * Jupiter's moon Europa is thought to have a giant ocean below its surface.
 * Jupiter's moon Ganymede is the largest moon in the solar system.
 * Jupiter is the third brightest object in the night sky, second being Venus and first being the Earth's moon.
 * Jupiter has more than twice the mass of all the other planets in the solar system combined.
 * Jupiter is considered an almost-star. The smallest red dwarf star was only 30% bigger than Jupiter.
 * Jupiter's red spot and the Earth are close to the same size. That means that there is a storm going on in Jupiter that is as big as the Earth!
 * Jovian in English means anything relating to Jupiter — the god or the planet. Sometimes the four outer planets are called the Jovian planets.

Jupiter is by far the largest planet in our Solar System: two and a half times larger than all of the other planets put together. It is the fifth planet from the Sun and one of the brightest planets as seen from Earth. Jupiter, along with Saturn, Uranus and Neptune, is sometimes called a "gas giant" because most of these planets are made up of liquid and gas.

How big is the planet?
Jupiter is 142,984 km or about 11 Earths in diameter at the equator. That makes it about one tenth as big in diameter as the Sun! You could fit about 1,400 Earths into the volume of Jupiter. It is 133,709 km or 10 Earths in diameter from pole to pole. Jupiter's rapid rotation (it spins around in under ten hours compared with 24 hours for Earth) makes it bulge out at the equator.

Jupiter's magnetic field is the largest single planetary thing in the Solar System. It is 26 million kilometers across, making it about 20 times bigger than the Sun. It has a tail that extends past Saturn's orbit. If it could be seen from Earth, it would appear to be five times the size of the full moon.

What is the surface like on Jupiter ?
The surface we see is not solid. This enormous planet has a relatively small solid and rocky core. Liquids and gases surround this core and blend with the atmosphere.

Jupiter is a cloudy, windy and stormy planet. It is always covered by a layer of clouds, and wind speeds of 600 km/h are not uncommon. The storms are visible as swirls, bands and spots. A particularly violent storm, about three times Earth's diameter, is known as the Great Red Spot. This storm has been in existence since at least 1831, and maybe since 1665. If the storm has existed since 1665, that would make it more than 300 years old!

The layer of clouds is divided into several bands. The lighter colored bands are called zones and the darker bands are called belts. The colors are caused by small changes in the temperature and chemistry. Each band rotates in the opposite direction from its neighbors. Along the edges where the bands meet, these winds collide and create swirling patterns.

The stormy atmosphere of Jupiter has flashes of lightning just like on Earth. However, while Earth's lightning strikes may be hotter than 50,000 °C, Jupiter's lightning strikes may go over 5,000,000 °C, which is a hundred times more than Earth lightning, and is more than the temperature of the sun's corona. The lightning is made by water near the tops of the clouds.

What are its rings like?
Jupiter's rings are dark and hard to see. They are made of tiny particles that meteors knocked off Jupiter's small inner moons and debris left over from comets and other objects that came close to the surface of Jupiter. In fact, until the Voyager spacecraft arrived near Jupiter and took closeup pictures of the rings of Jupiter, scientists didn't even know that it even had rings at all. Two rings are clearly from material that can be associated with two sets of the inner moons of the planet.

These are the names of the rings and their sizes:

Gossamer means in English anything that is delicate, light, and flimsy.

What is the planet's atmosphere made of?
In the outermost layer of Jupiter lie frozen Ammonia crystals. (Ammonia is a compound of hydrogen and nitrogen; its scientific designation is NH3.) crystals.

Jupiter's atmosphere is mainly made of hydrogen(H2). Near the surface, there is almost 90% hydrogen. Apart from this, the atmosphere has helium(He). Because of the high pressure, helium becomes a liquid further down in the planet. In addition, Jupiter has methane(CH4)(0.3%), hydrogen deuteride(HD)(0.003%), ethane(C2H6)(0.0006%), and least of all, water(H2O)(0.0004%).

Jupiter's temperature is very high. Because of this, scientists cannot tell all the materials the planet is made of. The outer core of Jupiter has hydrogen. The pressure present can make the gas solid. However, because of the very high temperature, the gas melts, and becomes liquid.

What are its moons like?
Jupiter has 95 known moons. There are four major moons that were discovered by Galileo in 1610, the first moons ever discovered around another planet. Those moons are Io, Europa, Ganymede and Callisto; they are named from characters in mythology closely associated with Jupiter. They are called the Galilean moons. There are often eclipses on Jupiter's cloud tops by the Galilean moons.

Amalthea Group
There are four small moons orbiting inside Io's orbit. That group is called the Amalthea group because Amalthea is the largest one. They are all small and potato shaped. Amalthea is very red. The material of Jupiter's rings came from meteors knocking it off of those moons. Amalthea(Greek:Ἀμάλθεια) in Greek mythology is a foster mother of Zeus.

Io
Io (pronounced EYE-oh) is Jupiter's closest major moon. It is 3643.2 km across, slightly larger than Earth's Moon. It has the most spectacular volcanoes in the solar system and molten sulfur lakes. Any craters formed by asteroids hitting the surface are quickly covered up by the volcanic activity. Io's core is made of molten iron and is surrounded by a rock shell. Unlike Jupiter's other moons, there is very little water on Io. Scientists think that when Jupiter was forming, it was hot enough to dry out Io, but not the other major moons. In Roman mythology, Io(Ancient Greek:Ἰώ) was a beautiful young nymph(Nymphs are divine spirits that animate nature and generally portrayed as beautiful young women.) that Zeus loved.

Europa
Europa (pronounced Eurṓpē) is 3,121.6 km across, about 10% smaller than Earth's Moon. It is made of silicates and has a layer of smooth water ice 10 to 30 km thick. The ice has long cracks in it and very few craters. It looks like the sea ice on Earth. The ice has slid around at the cracks. We believe there is liquid water under the ice as much as 100 km below the surface. There are also some large spots on the surface. In Roman mythology Europa was courted by Jupiter in the form of a bull. Europa (Ancient Greek:Ευρώπη) in Greek mythology was a Phoenician noblewoman who was abducted by Zeus to Crete (An island of Greece).

Ganymede
Ganymede is 5262.4 km across, making it 380 km wider than Mercury. It is Jupiter's largest moon and the largest moon in the Solar System. It has plate tectonics like Earth. There are older, darker regions and newer areas with grooves where the plates have moved. Newer craters have bright rays around them from material thrown up by impacts. Older craters look flat and faded because the icy surface does not hold the shape of the crater as well as rock does over long periods of time. Ganymede may have an iron and sulfur core with a silicate mantle and an icy shell. It may be similar to Io except with a layer of ice on it. In Roman mythology Ganymede was a beautiful young man who Jupiter kidnapped and made cupbearer to the gods on Mt. Olympus.

Callisto
Callisto is 4820.6 km across, about the same size as Mercury. It has many craters. Like craters on Ganymede, the older craters have faded. The largest crater is Valhalla. It has a bright center 600 km across with rings around it up to 3000 km across. Callisto is made of silicates and ice. There is a 200 km thick icy crust with a liquid water sea under it. In Roman mythology Callisto was turned into a bear by Jupiter's jealous wife Juno. Later Jupiter placed her in the stars as The Great Bear.

Other moons
The other moons are smaller in several groups outside the orbits of the major moons. There is also a small moon, Themisto and four groups of small moons that orbit very far from Jupiter.

How long is a day on this planet?
One Jupiter day is about 10 Earth hours long. You have to say "about" because different parts of Jupiter rotate about its axis at different speeds. This is caused by the fact that Jupiter is mostly gases that are in constant motion and sometimes going in different directions. Some efforts have been made to try and measure the rotation speed of the inner rocky core of Jupiter, but that has proved to be quite difficult to accomplish due to the magnetic fields that surround Jupiter and the very active radio energy that is generated by the atmosphere of Jupiter, which interferes with measuring techniques like radar that has been used to measure the surface of Venus and Mars.

How long is a year on Jupiter?
One year on Jupiter is 4,335 Earth days or 11.87 Earth years long.

A Jupiter year is about equal to four-tenths (or two-fifths) of a Saturn year. Thus after every two Saturn years, Jupiter has completed five full orbits about the Sun. So after 59 years, Saturn and Jupiter will be back in nearly the same position. When the orbits of two planets are simple ratios of each other like this, it is called a resonance.

How much would Jupiter's gravity pull on me?
If someone were floating close to the cloud tops of Jupiter, it would pull them down with a force about two and a half times as strong as the force of Earth's gravity.

Jupiter's rapid rotation causes the equator to bulge out. This would also cancel out about 10 percent of gravity's force on them if they were at the equator. The amount of this counteraction becomes lower the closer they get to the poles.

Who is it named after?

Jupiter (Latin Iuppiter) is named after the king of the Roman gods, also called Zeus in ancient Greece. The god Jupiter was known for causing lightning strikes on Earth. He is associated with the eagle and the oak tree.

Next Topic: Saturn

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

title: Wikijunior:Solar System/Jupiter


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Wikijunior:Solar System/Mercury

What is Mercury?
Mercury is the closest planet to the Sun. It is a terrestrial planet; that means a planet made from rock like Earth. It does not have a gas atmosphere, so there is no weather. For a long time, only one spacecraft, Mariner 10, had visited Mercury. In January 2008, the MESSENGER spacecraft went by Mercury. It has gone by Mercury two more times, and has started to go around the planet in 2011.

How big is Mercury?
Mercury is 4879 km across. Mercury's diameter is just less than half the diameter of the Earth. It is the smallest planet in the Solar System. Only dwarf planets like Pluto are smaller. Because Mercury is much closer to the Sun than the Earth, it can only be seen just after the sun goes down at night or shortly before it rises in the morning.

What is Mercury's surface like?
Mercury has craters like those on the Earth's moon. The largest crater on Mercury is the Caloris Basin. It is about 1300 km wide. It was created by a huge asteroid hitting Mercury. The asteroid was probably 100 km wide, but it hit Mercury's surface so hard that it made a much bigger hole.

The surface also has big cliffs called scarps. They were made long ago when Mercury cooled down. It shrank, causing the surface to get wrinkled in some places. This wrinkling created the scarps.

There may also be ice on the top and bottom of Mercury. Like the Earth, these areas (called poles) don't get much warmth from the Sun. Any ice there won't melt.

It is very hot during the day (over 400°C) because Mercury is so close to the Sun. At night it is very cold because Mercury loses almost all its heat since there is almost no atmosphere to keep the warmth there. The temperature can fall to almost -175°C.

How long is a day on this planet?
Mercury rotates (spins around) much more slowly than the Earth. It takes Mercury 58 days to spin once as viewed from a distant star. Because Mercury orbits the sun very quickly, a day on Mercury lasts longer than 58 days. If you were standing on Mercury at the equator and timed how long it took the sun to go from directly overhead to sunset to sunrise and then rise directly overhead again, it would take 176 Earth days. These long days and nights allow for the temperatures to rise as high, and fall as low, as they do.

How long is a year on Mercury?
Mercury has the shortest year in the Solar System. It is about 88 Earth days long.

It used to be believed that the same side of Mercury always faced the Sun. In order for this to be true, Mercury would have to take the same amount of time to rotate (spin around) as it does to circle the sun. From watching it carefully we now know that Mercury's rotation is somewhat faster than its orbit. Because of the way the orbit and rotation work together, on Mercury, a day (the time from one sunrise to the next) is actually almost twice as long as a year.

What is Mercury made of?
The center of Mercury is made of iron in partly-molten (liquid) form. We know that there is iron at the center because the planet generates a magnetic field. It contains more iron for its size than any other planet in the Solar System. The rest of Mercury, its thick crust, is made of a special type of rock called silicate rocks. There are craters near the poles that are constantly in shadow. Some of these craters contain ice. There is a huge crater on Mercury called Caloris Basin. It was formed when a comet hit the planet and lava or molten rock filled the impact crater. The round wall of this crater is over 2km tall.

How much would Mercury's gravity pull on me?
If you were on Mercury, it would pull you down less than half (38%)as much as the Earth. An item that weighs 100 pounds on Earth, would only weigh 38 pounds on Mercury.

Who discovered Mercury?
Nobody really knows who first discovered Mercury, but the first known recorded observations of it are from tablets in Assyria about three and a half thousand years ago, in the 14th century BCE. This was probably something like an informational article about Mercury's movements. In these tablets, Mercury is called (in translation) The Jumping Planet. Almost every ancient civilisation had their own written records and names for Mercury.

In 1639, an Italian astronomer named Giovanni Zupi observed that Mercury has phases, like the phases of the Moon, as it orbits around the Sun. This is evidence that it does orbit around the Sun, an idea that was fairly new at the time, suggested less than a hundred century earlier by Copernicus.

Before the twentieth century, it was a mystery to all the astronomers how long it took for Mercury to rotate. They solved this mystery in 1962, when some astronomers sent radar signals to Mercury, which then bounced back to Earth: it takes 59 days for Mercury to rotate.

It isn't easy to sent a space probe from Earth to Mercury, because Mercury is much closer to the Sun and therefore orbits the Sun much faster than Earth does. So a space probe would have to burn a lot of fuel to match its speed with Mercury, in order to orbit—or land on—the planet. In 1973, a space probe Mariner 10 was sent to take measurements of Mercury and map its surface. Because orbiting Mercury would be so expensive, Mariner 10 orbited the sun instead, and would take pictures each time it got close enough to Mercury. Unfortunately, when Mariner 10 finally ran out of fuel, it had only mapped about 45% of the surface. However, it also discovered that Mercury has an iron-rich core and a magnetic field. 29 years later, in 2004, another probe was launched, named MESSENGER. MESSENGER stands for MErcury Surface, Space ENvironment, GEochemistry, and Ranging. MESSENGER followed a complicated path that would slowly match speeds with Mercury without using much fuel. It passed by Mercury three times, and finally settled into orbit around Mercury more than six years after it was launched. By March 2013, MESSENGER had mapped 100% of the surface of Mercury.

Who is this planet named after?
In Roman mythology, Mercury (Latin Mercurius) was the messenger of the gods. He wore a hat and sandals with wings on them, allowing him to travel around the world very quickly. The planet Mercury was named after him because it moves faster than any other planet in the Solar System. It moves nearly 48 km every second! (Of course, the Romans didn't know that, but they could see how fast it moved across the sky.)The Greeks called this god Hermes.

Next Topic: Venus

title: Wikijunior:Solar System/Mercury


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Wikijunior:Solar System/Mars

Mars Facts: Mars is the fourth planet from the Sun. It is called a terrestrial planet because its outer layers are made of rocky material like the Earth.
 * Mars is red because of rust in the surface rocks
 * A volcano on Mars called Olympus Mons is the highest mountain in our Solar System.
 * Mars has polar ice caps that look like the ones on ../Earth/.
 * Mars has ancient river beds where scientists think liquid water flowed millions or billions of years ago.
 * The Tooting crater on Mars was named after a suburb in London because the discoverer "thought [his] mum and brother would get a kick out of having their home town paired with a land form on Mars".

How big is the planet?
Mars is the second smallest of the eight major planets in the Solar System. Only Mercury is smaller. It is nearly 7,000 kilometres (km) wide; just over half the width of the Earth. Its volume is about 15% of the Earth. Since a lot of the Earth is covered by water, the total surface area of the Mars is nearly as large as all of the land on the Earth. It is possible that its size may eventually permit human colonies.

What is its surface like?

The surface of Mars is a lot like a desert on Earth; it is very dry and dusty, but it is also very cold. There are a lot of loose rocks and dunes of fine sand. Crater impacts mark the surface, but these are not as common as on the Moon. One of the craters is the huge Hellas Planitia. It is about half the size of the continental United States. The southern half of the planet has more craters than in the north. The south is also higher in elevation.

There is an area on Mars called the Tharsis Bulge, which has four huge volcanoes. These volcanoes have not erupted for millions of years. The largest volcano is called Olympus Mons. It is 27 km tall, making it the highest mountain in the Solar System; more than three times higher than Mount Everest on Earth. It is 625 km across and takes up an area as big as the US state of Arizona. Mars also has a huge canyon called the Valles Marineris. It is much bigger than the Grand Canyon on Earth. It is 4000 km long, up to 7 km deep and up to 200 km wide. Scientists think that when the Tharsis Bulge was created, the surface of Mars cracked to form the Valles Marineris.

Like the Earth, Mars has ice caps at its poles. However, they are made from frozen carbon dioxide as well as ice. During the Martian winter at each pole, the cap grows as carbon dioxide from the atmosphere freezes. The cap shrinks again during the Martian summer. As on Earth, when it is winter at one pole it is summer at the other.

In some places, there are dry channels that look like they were made by running water. So, a long time ago Mars may have had lakes and streams made of water. Now all of the water is frozen into ice under the surface.

There is an atmosphere on Mars, but it is very thin. There is also much more carbon dioxide in it than oxygen. (Oxygen is the gas we need when we breathe in; carbon dioxide the gas we get rid of when we breathe out.) So, we would need spacesuits to visit Mars. The atmosphere helps protect the surface from smaller meteorites.

When Mars comes closest to the Sun, the atmosphere can stir up storms of dust. Some of these storms are gigantic; they can cover the entire planet in clouds of dust. Dust storms on Mars can last for hundreds of days, with wind speeds of up to 200 kilometres per hour. Huge storms like these have been seen from the Earth through telescopes.

How long is a day and year on this planet?
One day on Mars is only 39 minutes and 35 seconds longer than a day on Earth (1.026 Earth days). A year on Mars is almost two Earth years long (687 Earth days).

Much like the Earth, the axis of rotation of Mars is tilted at an angle. This tilt causes seasons on Mars as it travels around the Sun. Summer occurs on the half of the planet that is tilted toward the Sun, and winter on the other half. After half a Martian year has passed, the seasons are reversed. But these seasons are about twice as long as on Earth.

What is it made of?

The outer, rocky surface of Mars is called the crust. Most of the crust is made from basalt, a type of rock made when lava grows cold.

Like the Earth, Mars has a thick layer of rock below the crust called the mantle. The mantle is much hotter than the crust, and the mantle rock is partly molten. But the crust on Mars has grown thick, so the lava from the mantle no longer reaches the surface. There are volcanoes on Mars, but they are no longer active.

At the center of Mars is a core made of the metals iron and nickel. If Mars were the same size as the Earth, the core of Mars would be smaller than the Earth's core. So a larger amount of Mars is made out of rock. Because rock is lighter than the metals in the core, Mars has a lower density than the Earth.

How heavy would I be on Mars?

If you were on Mars, you would be lighter, as Mars' gravity only has a force about two fifths as strong as the that of Earth's. You could lift objects that weigh almost three times as much compared to similar objects here on the Earth. You could jump up almost three times higher, and it would take much longer to fall to the ground from the same height.

Even though it looks as though you would be like a comic-book hero on Mars, there are some things you couldn't do. Although a big rock would weigh less and you could pick it up, it would still have the same mass. If you tried to catch it, it would knock you over, and if it landed on you it would crush you. A car on the surface of Mars would need the same amount of power to speed up, although going uphill would be less of a problem. It may, however, need more room to stop. Because of the reduced gravity a vehicle would not "grip" the ground on Mars as strongly, but the constant mass would keep the vehicle moving just as strongly, making it easy to go into a skid.

Who was it named after?
In Roman mythology, Mars was the god of war and agriculture. The planet Mars was named this because the planet looks red like blood, from rust in its surface rocks.

Who discovered Mars?
Nobody knows, but the earliest records we know of were by Ancient Egyptians, more than 4000 years ago, noting Mars' movement. On one pharaoh's tomb, named Seti I, Mars is drawn on the ceiling. The Babylonians (in the Middle East), Chinese, and Greeks also studied Mars more than 3000 years ago. The Greeks learned about Mars from the Babylonians, and since the Babylonians called it their god of war, named Nergal, the Greeks called it their own god of war, Ares. Exploration of Mars was first attempted in 1960, with Mars 1. It failed, along with several other missions by the Soviet Union in the 1960s. The first successful mission to Mars was in 1964, by Mariner 4, by the U.S. Most of the other Mariner missions to Mars were successful. The last Mariner mission to Mars, Mariner 9, got there in the midst of a dust storm, and orbited the planet for several months before it could get a good look at the surface. So far, all these missions were flybys or orbiters. The first spacecraft to land on Mars was Viking 1 in 1976. Viking 2 landed 19 days later. Together, they took many good pictures of Mars' surface. Next Topic: Asteroid belt

title: Wikijunior:Solar System/Mars


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Wikijunior:Solar System/Saturn

Saturn Facts:
 * If you could find a bathtub big enough, Saturn would float in it.
 * Some of Saturn's moons control the width of its rings. These are known as shepherd moons.
 * Although it is made mostly of gases, scientists believe Saturn has a small rocky core.

Saturn is the sixth planet from the sun, and is one of the gas giants. Although it is very large – almost ten times wider than Earth – it is mostly gas and liquid, and therefore very light. Its distinctive rings aren't solid, they're actually loose clusters of moving particles of rock and ice.

How big is the planet?
Saturn is 120,536 km or 9.449 Earths wide at the equator.

What is its surface like?
Saturn is mostly gas and liquid. Saturn may have a small core of rock and ice. The atmosphere has bands, but they are not as colorful as Jupiter's.

What are its rings like?
Saturn's rings are composed of rock and ice particles ranging in size from specks of dust to the size of a house. Some particles might even be a few kilometers wide! The particles in the rings are actually spaced far apart. It would be easy to pass through the rings.

What are its moons like?

Saturn has 146 moons, and many of them have names. The size of Saturn's moons and the size of the chunks of ice in its rings are similar, which means that we can never know the exact number of moons. New moons are still being discovered. Saturn's biggest moon is named Titan, and is large enough to be a planet in its own right!

Shepherd moons
There are small potato-shaped moons in or near Saturn's rings. They control the ring particles with their gravity. That is why they are called shepherd moons. Six of them are known, and there may be more.

Mimas
Mimas is mostly made of water ice with a small amount of rock. It has a large crater for its size called Herschel. It is 130 km across, making it about a third as big as Mimas. The crater makes Mimas look like the Death Star from the Star Wars movies.

Enceladus
Enceladus is made of ice. It is denser than the other icy moons. That suggests it also has some rock inside. It has smooth areas, cracks and some craters. The smooth areas are younger. Craters there have been erased within the past 100 million years. Water vapor was found over a smooth area around the south pole. The cracks and grooves suggest tectonics similar to Ganymede's. Some ridges similar to Europa's ridges were also found. Those suggest oceans like Europa's under some areas of Enceladus. Tidal forces from Dione could be powering some of this activity. It is because Enceladus orbits Saturn twice for every orbit by Dione. This makes Dione and Saturn tug on Enceladus. This is similar to how Europa and Ganymede's tidal forces on Io power Io's volcanoes.

Tethys
Tethys is an icy moon that has many craters, including the huge Odysseus. It is 400 km across, 1/5th as big as Tethys is. The crater had become flattened because the icy material does not hold its shape as well as rock would. There is also a large valley called Ithaca Chasma. It is 3 to 5 km deep, 100 km wide and 2000 km long, three fourths of the way around Tethys.

There are two moons, Telesto and Calypso, which share Tethys' orbit. Telesto is ahead of Tethys and Calypso is behind it.

Dione
Dione is made of lots of ice and there may be some rock in its core. It has lots of craters. The craters are flattened because the ice does not hold their shape as well as rock. One side has bright white lines that are fractures. Two moons share Dione's orbit. Helene is ahead of Dione and Polydeuces is behind it.

Rhea
Rhea is an icy moon similar to Dione with some rock in the core. It has many craters mostly on one side, and the other side has some bright white icy areas.

Titan
Titan is the largest moon of Saturn and the second largest one in the solar system. It is the only moon in the Solar System that has a thick atmosphere. The atmosphere is made of nitrogen, argon, methane and various organic compounds. Its surface has light and dark areas and few craters. The Cassini probe discovered a huge crater 440 km wide.

Hyperion
Hyperion is made of water ice with a little rock. It is potato shaped. It wobbles instead of rotating in the same way other moons do.

Iapetus
Iapetus is almost entirely ice. It has a light area called Roncevaux Terra that has craters. There is a big dark area called Cassini Regio that covers half of Iapetus. The dark material may be from Phoebe. Some of it is on the bottom of craters. Some huge craters and a ridge have been discovered in Cassini Regio by the Cassini probe. The ridge stretches 1300 km along the equator. It is up to 20 km high, which is over 2.26 times higher than Mount Everest. More huge craters were found in Roncevaux Terra when Cassini went by Iapetus again.

Phoebe
Phoebe is made of ice and rock. It looks dark because it has a layer of dark material on the outside. It also looks rough.

Other moons
There are two groups of small outer moons. Phoebe is part of the second outermost group.

How long is a day on this planet?
One day on Saturn is about 10 hours and 39 minutes in Earth time.

How long is a year on this planet?
One year on Saturn is about 29.46 Earth years long. That is 10,760 Earth days!

What is it made of?
Saturn has a rocky core. Around the core, there is ice. Above the ice is liquid metallic hydrogen. On top of that is gaseous hydrogen. There is no place where the hydrogen suddenly turns from a gas to a liquid.

The gaseous hydrogen makes up most of Saturn's atmosphere. Other gases there include helium and some other gases. There may be rain made of helium falling through the hydrogen. There is also ammonia on the surface.

How much would Saturn's gravity pull on me?
If you were floating close to the cloud tops of Saturn, it would pull you down with a force only a little stronger than the force of Earth's gravity. The effects of Saturn's large radius and its mass almost cancel each other out, making the force only a little bigger. So, if you weighed 100 lbs. on Earth, you would weigh 106 lbs. on Saturn.

Who is it named after?
Saturn is named after the most important Roman god of agriculture and harvest time. He taught people how to farm. He was the father of Jupiter. Saturday is named after him.

Next Topic: Uranus

ar:ويكي الأطفال:نظام شمسي/زحل Wiki junior Sunčev sistem/Saturn Wikijunior_Sonnensystem/_Saturn Wikichicos/Sistema_Solar/Saturno fr:Wikijunior:Système_solaire/Saturne nl:Wikijunior:Zonnestelsel/Saturnus pl:Wikijunior:Układ_Słoneczny/Saturn Wikijunior_Aurinkokunta/Saturnus

title: Wikijunior:Solar System/Saturn


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Wikijunior:Solar System/Uranus

Uranus, the seventh planet from the Sun, was discovered by William Herschel on March 13, 1781.

How big is Uranus?
Uranus is 51,118 kilometers or about four Earths wide. It is the third widest and fourth heaviest planet in the Solar System.

What is the surface of Uranus like?
Uranus does not have a surface that you could stand on without going deep into the atmosphere. Under the atmosphere, there may be an even mixture of rock and ice.

What are the rings around Uranus like?
Uranus has eleven rings. They are dark in colour and very hard to see. They were discovered by accident in 1977. Scientists were studying a bright star near Uranus. However, the star's light was blocked before and after it disappeared behind Uranus. From this, they figured out that Uranus has a ring system.

What are its moons like?

Uranus has 27 known moons, which places it third in the Solar System for number of moons. The five main ones are Miranda, Ariel, Umbriel, Titania and Oberon.

Miranda
Miranda is the smallest and closest of Uranus's major moons. It is mainly made of ice and rock. Miranda's surface has grooves, cliffs, and valleys. The moon was named after a character in The Tempest, a play by Shakespeare.

Ariel
Ariel is made of rock and ice. Ariel has many valleys, but not many craters. Ariel was named after a character in the poem The Rape of the Lock by Alexander Pope. Ariel is also a spirit in The Tempest by Shakespeare.

Umbriel
Umbriel is made of lots of ices and some rock. It is also the darkest of Uranus's major moons. Umbriel was named after a character in the poem The Rape of the Lock by Alexander Pope.

Titania
Titania is the largest moon of Uranus. It is mostly ice and rock. The surface is covered with canyons. It was named after the Queen of the Fairies in A Midsummer's Night Dream, a play by Shakespeare.

Oberon
Oberon is the outermost of the major moons of Uranus. It is made of the same things as Titania. It has many craters. Some of them have white rays around them and dark crater floors. It was named after the King of the Fairies in A Midsummer's Night Dream.

Other Moons
There are 13 tiny moons known to be orbiting Uranus inside Miranda's orbit. Nine more tiny moons are known to be in big orbits beyond Oberon's orbit.

How long is a day on Uranus?
One day on Uranus is about 17.24 Earth hours long. Uranus spins on its side, maybe because of a big impact early in the history of the Solar System.

How long is a year on Uranus?
One year on Uranus would be 30,708 days or 84 years on Earth.

What is Uranus made of?
Unlike Jupiter and Saturn, Uranus is thought to be made mostly of rock and ice. The gases in its atmosphere are 83% hydrogen, 15% helium, and 2% methane. Other gases found in smaller amounts are ammonia, water, and methane. Uranus' blue color comes from methane clouds, which absorb red light and reflect blue light.

How much would Uranus's gravity pull on me?
If you were floating close to the cloud tops of Uranus, you would be pulled down with a force about 89% of Earth's gravity.

Who is Uranus named after?
Uranus was named after Ouranos, the Greek name for the sky. Ouranos was the ancient Greek deity of the heavens, the earliest supreme God. According to Greek mythology, Ouranos was the husband and son of Gaia, Mother Earth.

Next Topic: Neptune

title: Wikijunior:Solar System/Uranus


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Wikijunior:Solar System/Neptune

How big is this planet ?
Neptune is very similar to Uranus in size. Its diameter is only slightly smaller, at 49,528 km wide. It is almost as big as four Earths in length.

What is its surface like?
The atmosphere of Neptune has some dark blue spots. When the Voyager probe went by Neptune in 1989, it saw a large one called the Great Dark Spot. In 1994, it vanished, but later reappeared. There is also a large white cloud nicknamed "Scooter." It goes around Neptune every 16 hours. The winds of Neptune are very fast, blowing at up to 2000 km per hour(the fastest in the entire solar system). That is about four times faster than the fastest recorded tornado on Earth.

What are its rings like?
Neptune has some faint rings that are dark and hard to see. There are clumps in some parts of the rings where the material is denser.

What are its moons like?
Neptune has 14 moons. There could be more.

Inner Moons
There are five small potato-shaped moons orbiting close to Neptune.

Proteus
Proteus is a dark moon about 418 km across. It has an irregular shape. In Roman mythology Proteus was a sea-god who could change into any shape he wanted.

Triton
Triton is the largest moon of Neptune. Scientists think that it is a lot like Pluto. It is 2700 km across. It is made of rock and ice. It has a surface temperature of −235 °C Triton has a very thin atmosphere made up of nitrogen and a little methane.

There are volcanoes that have eruptions of liquid nitrogen, dust or methane compounds. The eruptions happen because of the seasons. There are few craters because the eruptions cover them up. There are ice caps that change sizes with the seasons. There are also ridges and valleys. They may have formed because of repeated freezing and thawing.

An interesting thing about Triton's orbit is that it goes around Neptune in the opposite direction that Neptune's rotates. Because of this, scientists think that Triton was captured by Neptune long ago. In Roman mythology, Triton was the son of Neptune.

Nereid
Nereid is an irregularly shaped moon about 340 km across. Its orbit is very eccentric or noncircular. It may have been captured by Neptune or moved into the eccentric orbit by Triton's gravity when Triton got captured. In Roman mythology Nereids were sea nymphs.

Outer Moons
There are five other known moons. They are small potato-shaped moons far from Neptune. There might be more we haven't seen yet.

What is the Mass ?
A day on Neptune lasts 16 hours and 7 minutes.

How long is a year on this planet?
One year on Neptune is about 165 Earth years, or 60,265 days.

What is it made of?
Neptune is made of rock and metal in the core. The core is probably bigger than Uranus's because Neptune weighs more, but is the same size. Around the core is rock, water, ammonia and methane. The atmosphere is made of hydrogen and helium. Lower down in the atmosphere, there is methane and ammonia too. The methane makes Neptune look blue-green.

How much would Neptune's gravity pull on me?
If you were floating close to the cloud tops of Neptune, it would pull you down with a force only a little stronger than the force of Earth's gravity. The effects of Neptune's larger radius and its mass almost cancel out, making the force only a little bigger.

Who is it named after?
Neptune is named after the Roman god of the seas, also known as Poseidon in ancient Greece.

Next Topic: Pluto

title: Wikijunior:Solar System/Neptune


text:
Celestia/Acknowledgements

Celestia was created by Chris Laurel.

The Celestia AUTHORS file lists the following people:

 * Chris Laurel
 * Clint Weisbrod
 * Fridger Schrempp
 * Bob Ippolito
 * Christophe Teyssier
 * Hank Ramsey
 * Grant Hutchison
 * Pat Suwalski
 * Toti
 * Da Woon Jung
 * Vincent Giangiulio
 * Andrew Tribick
 * Dmitry Brant
 * Hleb Valoshka
 * Levin Li
 * Łukasz Buczyński

Other contributors to the Celestia software distribution are cited in the README file.

Authors who have generously contributed material from their previously written documentation to this wikibook include:

 * Chris Laurel
 * Selden Ball

Add yourself here if appropriate

People who have made original contributions to this wikibook include:

 * Chris Laurel
 * Selden Ball
 * John Van Vliet
 * LukeCEL
 * SevenSpheres

add yourself here if appropriate

Many other people have also made valuable contributions to the Celestia community in various ways. Those that deserve special mention here are:

 * add deserving individuals (not yourself, of course!) with their permission here

And if we've inadvertently left out anyone you think should be mentioned, please add them!

title: Celestia/Acknowledgements


text:
Celestia/Scripting

Introduction
Typing commands on the keyboard can be tiring and error prone. If you are using Celestia to show the universe to others, a script may be an effective way to tour the stars.

Types of Scripting
Celestia supports two different Scripting languages, CEL and CELX (Lua). These can be used to add new functionality to the program, or to run educational activities.

CEL scripting
See the page Celestia/Cel_Scripting

CELX scripting
See the page Celestia/Celx_Scripting

Other Languages
You can use any other language you want if it can pass commands to the operating system's command interpreter. It can issue the command to run Celestia and can include on that command line the instruction to run a .CEL Celestia script or .CELX Lua script.

When invoked from a command line, Celestia can be passed the name of a .CEL or .CELX script to run at startup:

./celestia --url name-of-script.cel

When the command line includes the qualifier "--once", the command line will be passed to the running copy of Celestia instead of starting a new copy of the program. (note: use two hyphens)

./celestia --once --url name-of-script.celx

(Starting with Celestia v1.3.1, scripts may be in any folder. Previously they had to be in Celestia's "root" folder.)

title: Celestia/Scripting


text:
User:Kusti

At the moment I'm interested in MacOSX Cocoa development. Other interests will follow, no doubt.

title: User:Kusti


text:
User talk:80.58.37.44

Your browser doesn't support Unicode. You break pages with non latin characters. Your editions were reverted. You should use Mozilla instead. Thanks. Yann 22:37, 8 Nov 2004 (UTC)

I'm so sorry. I have changed my usually computer and I didn't knew I've change these pages.

title: User talk:80.58.37.44


text:
Wikijunior talk:Solar System/The Sun

media
hey check out the image of the sun in the wikipedia aricle sun it pulls up a moving image really cool actually --Larsie 23:06, 8 Nov 2004 (UTC)

 * I don't see it. There are two still images on that page, but I don't see any moving ones :-( Theresa knott 06:13, 9 Nov 2004 (UTC)

 * I think he's talking about http://upload.wikimedia.org/wikipedia/en/7/74/SOHO_solar_flare_sun_MPEG_20031026_eit_304.mpeg . Gentgeen 06:24, 9 Nov 2004 (UTC)

 * Oh I see. Yes it is cool. Larsie was that you who tried to add the image to this module direct from the wikipedia page? Because it doesn't work. All I see is a message "Missing Image". When you put an image link in, the software checks to see if it's here, if not it checks wikicommons -and that's it. It doesn't check wikipedia. Theresa knott 06:41, 9 Nov 2004 (UTC)

well it should ;)--Larsie 17:12, 9 Nov 2004 (UTC)

so cool —Preceding unsigned comment added by 68.151.66.107 (discuss • contribs) 03:21, 15 December 2005

warning
This page is going to need the standard do not directly look at the sun warningGeni

 * Good idea, we should also show how to make a simple pinhole camera for safe viewing of the Sun. Theresa knott 20:17, 14 Nov 2004 (UTC)

Distance
I added the distance to the sun, as that should be in there somewhere, but if it should be moved to another section that's fine. --Asbestos 23:45, 14 Nov 2004 (UTC)

Sample spread
I whipped this up. It's a little sparse, and some of the orange text overlaps the sun picture, and the colors got really intense when I went from CMYK to RGB, but it's a start. Let me know what you guys think. LockeShocke 00:57, 1 Mar 2005 (UTC)

 * problem is that one of the uses of what we are doing is meant to be a website and webistes compoed of pictureas are less then idea on dialupGeni 02:59, 4 Mar 2005 (UTC)

 * Yeah, but these are going into print sooner or later. I thought that was the whole point. LockeShocke 22:57, 4 Mar 2005 (UTC)

 * both. They are meant to end up in print and as a website (not here).Geni 23:24, 5 Mar 2005 (UTC)

 * The problem is that images help learning things as well as they encourage kids to keep/get their interest. Gotta walk a fine line again, huh? ;) --Telcontar 00:59, 18 Mar 2005 (UTC)

That whole thing could be done with no pics (or just one depending on how you do it), just html and css. would take some time and some know-how but its possible. I think as a mock up it looks pretty damn good. —Preceding unsigned comment added by The bellman (discuss • contribs) 04:56, 8 June 2005

Solar Wind
Is a section needed on the Solar Wind? — RJHall 20:18, 31 May 2005 (UTC)
 * Okay I added a short section. Wasn't sure how much detail to add. — RJHall 22:44, 16 Jun 2005 (UTC)
 * I apologize for editing/deleting the words that you put in for the solar wind. I tried to incorporate the major ideas that you had, but it has been substantially reworded as part of an overall expanded explaination of the solar atmosphere in general.  I also feel that the discussion of the aurora needs to be put on the Earth page instead, although perhaps we need to add something about auroras in general here, as they also occur on all of the other planets with an atmosphere (Does Mercury have aurora?  Really, I don't know.)Rob Horning 06:43, 24 Jun 2005 (UTC)

Possible Minor Clarification for How Bright a Sunspot is
Right now, the brightness of a sunspot is compared to an electric arc. Would it be possible to compare it with a light bulb of the appropriate wattage instead? I think that might be clearer to young readers. —Preceding unsigned comment added by 192.160.51.70 (discuss • contribs) 13:17, 23 June 2005

Suggestion of possible warning message
My concern here is that with the mention of various aspects of the Sun, that children will want to look at it. While that is not a bad thing, perhaps we should warn children that looking directly at the Sun is dangerous - viewing the Sun should only be done with appropriate protective eyewear or a protective apparatus (I don't think sunglasses count). I saw that there was a blurb hidden within the text, and there's a previous comment here about it. Could we put it in a little more visible place? Maybe the top? —Preceding unsigned comment added by 13:38, 23 June 2005 (discuss • contribs) 192.160.51.70
 * I added a warning message into the 'fact box' section. This is a valid point.  BTW, I would personally (Non-NPOV here... so I don't think it is easy to put into the module) recommend using welding goggles or other similar filters.  Solar observatories use somewhat similar filters that are even stronger....they look like black glass or even obsidian until you see the sun through it.  If you ever get a chance to see solar prominences through one of these telescopes, it is an experience that is nothing short of incredible, and photos just don't do it justice. (I had my first experience at Mt. Wilson observatory in Los Angeles.)Rob Horning 07:06, 24 Jun 2005 (UTC)

Better basic facts
I really dislike most of the "Sun Facts" on this page. For example, "The sun is really a star" suggets that it might be something else. Perhaps just "the sun is the closest star to earth"

The one about the sun blowing up should be replaced with something that explains how light takes 8 mins to travel from the sun the earth.

And also, ALL bodies that rotate around an axis move faster along the equator because the distance of the circumference is greater at the equator than at the poles. Perhaps this should be changed to "The Sun rotates about an axis, just as Earth does" or something. Doom of Doom 26 Jul 2005

 * I completely agree. --Laura Scudder | Talk 06:04, 31 July 2005 (UTC)

 * Actually, the sun "swirls" around on its axis. The equator completes a rotation sooner than the higher latitudes.  I think it is 25 Earth days for the equator, 35 for the higher latitudes.  When we talk about the surface of the Sun, we are talking about the photosphere, which is a gas.  Presumably, the Earth's atmosphere swirls around the Earth's axis in a similar way. --SV Resolution 04:22, 24 August 2005 (UTC)

Photoshpere
On section "What are sunspots?", "photoshpere" is mentioned without previously defined and without a short explanation: "The Umbra is about 2000 °C (3600 °F) cooler than the photosphere and only looks dark in relation to its surroundings." —Preceding unsigned comment added by Agro1986 (discuss • contribs) 08:40, 16 August 2005

Move Heliopause and Zodiacal Light to "Solar System"?
I don't think either of these things are part of the sun. What do you all think?--SV Resolution 15:22, 21 August 2005 (UTC)

Well, ok, Heliopause *IS* part of the sun. But maybe Zodiacal light is not so much a part of the sun's atmosphere. Since Zodiacal Light is the light reflected from interplanetary dust, I think it is only part of the sun in the way that the asteroids are part of the sun. I am thinking Zodiacal Light should be moved to the "The Solar System" module, perhaps right after "asteroids". I might just be bold enough to do it. --SV Resolution 04:18, 24 August 2005 (UTC)

Voyager recorded "the bump" ???
In May 2005, the Voyager I spacecraft went through this region recorded the bump.

 * not sure what this means b ut it is unclear and need some sort of fix Pedant 19:47, 3 October 2005 (UTC)

You are correct. That's bad writing. --SV Resolution 13:05, 4 October 2005 (UTC)

Proofreading Done
I have proofread this entire page following the plan, except for the references section. I am not sure what the current policy is about locking the page to prevent it from becoming "unproofread". Who is the admin for this area?

Dubious factoid
Copy paste from a post I just made on reddit
 * "This seems way off to me. Order of magnitude approximations: volume of a pinhead is about a mm cubed density of sun's core is about 150 g per cm cubed so the piece would way 0.15 g heat capacity of hydrogen gas is about 15 J per g per degree K at ambient pressure and temperature, which probably bears little resemblance to the heat capacity of material in the sun's core. I'll use 150 J/gK as an upper bound. Temperature at the sun's core is about 15000000 K, so with simple arithmetic we get the thermal energy in that piece of sun is about 300000000 J, which is equivalent to about 0.1 tons of TNT exploding. While impressive, this is nowhere near sufficient to kill someone at 100 miles. Atomic weapons equivalent to millions of tons of TNT are survivable at less than that range. Unless my value for heat capacity was off by over a factor of 10000, this post is completely incorrect.

tl,dr, OP lies (or is at least misinformed)" Unless someone can give a better source for that factoid it should be removed. Bouer. —Preceding unsigned comment added by 129.97.131.0 (discuss • contribs) 06:13, 25 November 2014

title: Wikijunior talk:Solar System/The Sun


text:
User talk:200.108.223.149

Hi,

I like the new navigation markers (<^>) that you put in. They are very simple, elegant and fairly intuitive. It also makes it simple to go through sideways through the documentation, page by page.

However, I have a few minor concerns for which you may already have a solution:

 * I wonder how well the <^> alone will work once the documentation pages become nested several layers deep. In the Menu documentation section, for example, we are starting to  go 3 layers deep in the preference section, i.e.:

Online OsiriX Documentation Table of Contents > OsiriX Menu > OsiriX General Preferences

With the <^> system, it will be clear how to go up the tree from "Here" to "There" or from side to side, but I'm not sure it will be completely clear to the user where "Here" is and how far down the tree or to the side "There" is.

 * The <^> alone doesn't seem to provide a quick way to get back to the front page, or any arbitrary distance up the tree. The original "bread crumb trail" method I started with  allows this, although it takes up a lot more screen space and doesn't allow one to move to either side.

 * As long as the documentation is only 2 layers deep, it's not hard to know which page the <^> should point to next. However, once we get deeper than that, it's less clear.  Should the > lead to the next section of the same level, or should it go to the first page of the next section no matter how far down the tree it is?

 * It also seems to me that once the documentation gets only slightly more complex, it could become a real headache to keep all of the <^> updated properly, especially if we decide to add a new page or rearrange the order of the pages.

Can you think of some way we can resolve these issues? I'd love to find some solution that keeps all the benefits of both systems. Whatever system we arrive at, I hope that it will be one that will make it easy to keep the different multilingual versions of the documents congruent.

However, perhaps I am thinking too linearly -- maybe I should be thinking more in a hypertext manner. :-) Perhaps there is already some cool Wiki solution or convention for handling this of which I am unaware.

Best Regards,

--Mrich 23:55, 8 Nov 2004 (UTC)

title: User talk:200.108.223.149


text:
User:SiowWeiming

Siow Weiming 5th year medical student United Kingdom

title: User:SiowWeiming


text: User talk:Rdsmith4

title: User talk:Rdsmith4


text:
World History/The First Chinese Dynasties

The Mythical Period
According to legend, Chinese history began with a succession of three rulers - half-human, half-animal - followed by five emperors. The three rulers - Fuxi, Nüwa, and Shennong - each are credited with contributing to the early people's lifestyles:

 Fuxi - traditional reign began in 2852 B.C. Introduced domestication of animals and founded the basic social structure of family life. Nüwa - wife of Fuxi. She is also credited for his accomplishments. Shennong - divine farmer who taught agriculture to the settled peoples.

Following this period, five successors introduced the basic aspects of culture:

 Huangdi, or the Yellow Emperor - traditional reign lasted from 2698 B.C. - 2598 B.C. As with the aforementioned rulers, his existence may be mythical as well; the period of his reign occurred about one millennium before Chinese history was recorded. Nevertheless, he has been regarded as the ancestor of all Han Chinese - the largest ethnic nationality in all of China. Some of his achievements include the institution of Chinese characters (thus leading to literacy), the development of silk (from silkworms), and the establishment of the principles of Traditional Chinese medicine. Zhuanxu - credited with the creation of the Chinese calendar, as well as the introduction of religion and astrology (this may or may not correspond to the Chinese zodiac). Emperor Ku - dates suggest he ruled from 2435 B.C. - 2356 B.C.; however, little else is known about his contributions. Emperor Yao - reign lasted from 2356(?) B.C. - 2255 B.C. He is believed to have served as a "role model" for future rulers due to his dignity and diligence. Some also credit him for creating the popular board game, "weiqi" (also known as "Go"). Emperor Shun - reign lasted from 2255 B.C. - 2205 B.C. Although he did not follow the bloodline of Yao (Shun was a peasant), he was chosen to succeed the former because of his 'devotion to his (own) father'. Shun's devotion also set an example for future rulers.

Like Yao, Shun also chose his successor rather than continue the family line. He appointed Yu, a paragon who helped to drain the floodwaters around much of eastern China. At this point, archaeological evidence suggests that he founded the Xia Dynasty in 2205 B.C.

The Xia Dynasty (c. 2205 B.C. - 1766 B.C.)
Because Yu was also a Chinese mythological figure, the existence of the Xia dynasty is somewhat debatable, as most of it is based on cultural legends. Nevertheless, archaeological evidence (dated from the Shang and later dynasties) shows that an early farming culture was established around 2205 B.C., centralized in the Huang (Yellow) River Valley and the surrounding region. The early peoples of the Xia were also believed to have created a primitive writing system, though this is also questionable as no written records have yet been found near that region.

Based on available evidence and findings, the Xia developed sufficient agricultural methods and techniques and generally experienced considerable prosperity. Lack of irrigation and flood protection made the region prone to frequent floods and other natural disasters, however. Eventually, the peoples of the Xia were overthrown by rebels c. 1760 B.C., who in turn established new rule in the Huang River Valley.

The Shang Dynasty (c. 1766 B.C. - 1122 B.C.)
Upon establishment c. 1766 B.C., the Shang developed a theocratic government centered around the capital city of Anyang (south of the Huang River, in present-day Henan province). Shang kings were believed to fulfill sacred rather than political purposes; thus, a council of chosen advisers administered various aspects of the government. The dynasty claimed rule over much of northern China, but in reality its control and influence did not spread as far and wide. Farther away from the capital, aristocrats who pledged support to the king governed local areas and managed affairs such as defense, militia, and tax collection. The border territories of Shang rule were led by chieftains who gained the right to govern through connections with and/or acceptance from the royalty.

Society and Class Divisions
Citizens during the Shang dynasty can be classified into four social classes: the king & aristocracy, the military, artisans & craftsmen, and peasants.

The aristocracy were centered around Anyang, the Shang capital, and conducted governmental affairs for surrounding areas. Regional territories were also controlled by the wealthy, although their roles were limited to local districts as opposed to the entire state.

Following the aristocracy came the Shang military, who were respected and honored for their skill. There were two sub-divisions: one for infantry (foot soldiers) and one for chariot warriors. The latter were noted for great skill in warfare and hunting, and evidence has shown that horses and other cavalry were utilized by the Chinese during the late Shang period, c. 1250 B.C.

Artisans and craftsmen comprised the 'middle class' of Shang society. Their largest contribution was their work with bronze, which the Chinese developed as early as 1500 B.C. Bronze weapons and pottery were commonly made, but the most prominent creations included ritual vessels and treasures, many of which were discovered via archaeological findings in the 1920s and 1930s. Shang aristocrats and the royalty were believed to have been buried with large supplies of bronze valuables, particularly wine vessels and other ornate structures.

At the bottom of the social ladder were the peasants, the poorest of Chinese citizens. They comprised the majority of the population, and were limited to farming and selling crops for profit. Archaeological findings have shown that masses of peasants were buried with aristocrats, leading some scholars to believe that they were the equivalent of slaves, but other scholars have countered that they were similar to serfs. Peasants were governed directly by local aristocrats.

Early Chinese Culture
The Shang dynasty gave birth to much of modern Chinese culture, and thus set the 'template' for further development by future dynasties.

Chinese writing had its origins in Shang culture as a means to unify the various dialects spoken by regional Chinese. The earliest forms of writing were depicted using pictographs, where primitive drawings conveyed symbols, objects, and ideas. Although not as detailed as Egyptian hieroglyphics or other ancient forms of writing, the pictographs served as a basic form of written communication. As years passed and the language grew, ideographs replaced these pictures, and used more simplified symbols to communicate. Combinations of symbols produced characters, which could be used to express more complex ideas. Over time, more and more characters became incorporated into the Chinese language. Scribes learned the writing system to record historical accounts and other royal documentation; they used calligraphy as a 'script' to record such observations.

Shang religion was characterized by a combination of animism (spiritual control of the world) and ancestral respect and worship. Natural and mythological symbols such as the moon, sun, wind, rain, dragon, and phoenix were controlled by respective gods, to whom peasants prayed for bountiful harvests. Festivals became common and celebrated the gods in hopes for a good spring harvest. The great god Shang Di, believed to rule over humanity and nature, was consulted by rulers for advice and wisdom. Thus, Shang kings believed themselves to be divine rulers. Priests frequently consulted both the gods and rulers as well - they inscribed divine questions on oracle bones (dried animal bones, especially turtle shells) and heated them until a series of cracks appeared on the surface. These cracks were interpreted in an attempt to seek answers to such questions.

The Chinese also established a lunar calendar that was used to predict and record events such as harvests, births, and deaths (of rulers and peasants alike). The system assumed a 29-day month that began and ended with each new moon; twelve lunar months comprised one lunar year. Priests and astronomers were trained to recalculate the lunar year and add enough days such that each year lasted 365 days. Because the calendar was used to time both crop planting and harvest, the king had to employ skilled astronomers such that predicted dates (and successes) of annual harvests would help him maintain support from the people.

The Zhou Dynasty (1122 B.C. - 256 B.C.)
Toward the end of the Shang dynasty, a new faction of rebels amassed within the empire. Naming themselves the Zhou, they overthrew the last of the Shang kings in 1122 B.C. and instituted the Zhou dynasty, with its capital at present-day Xi'an.

"Mandate of Heaven"
The Zhou claimed that their rule had been justified by the mandate of heaven, the idea that the king was chosen by the gods (as the "Son of Heaven") but could be deposed if he ruled unfairly or tyrannically. In other words, the Zhou believed that the last Shang king lost his mandate and 'transferred' it to the new ruler, who in turn became 'blessed' by the gods. The mandate of heaven was also used to justify the demise of the Xia dynasty as well, and would be repeated by future dynasties.


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Talk:Turkish

It looks like there's a confusion in present continous and present tenses. For an example, "I go" is almost never used in the meaning of "I am going" in Turkish. The first is translated as "giderim" and the latter as "gidiyorum". This works as it would in English. But, sometimes a literal tranlation would give a wrong meaning; "I understand" should be translated as "Anladım" (I understood).

Splash Screen
I read somewhere the splash screen isn't a good idea, or that helpful, should we delete it? --Uzbekscholar 06:17, 3 November 2007 (UTC)

some improvements needed
minute details of pronounciation are too intricate and unnecessary to introduce this early. (noone really will understand the difference if you pronounce 'deyil' or 'deghil' and noone really woud attempt to pronounce 'limon' with a back-L) --Dogu 16:40, 5 Apr 2005 (UTC)

The big tidy up
Hey, I've cleaned up to some extent this Wikibook, splitting it into seperate pages, and added a picture. I hope everyone is happy with this and good luck with continuing the book. Serge 00:56, September 8, 2005 (UTC)

Thank You
I'd just like to express my appreciation for those who are working on this book. I am eager for it to be developed further so that I may learn more Turkish. So far, it is well-structured and easy to understand. Keep up the good work! --RealGrouchy 05:12, 25 January 2006 (UTC)

New TOC template
Hi everyone... this is my fist time contributing to a wikibook, though I've been a Wikimedia fan for a while now. Since I'm a novice Turkish speaker, I probably won't contribute to the content as much as I will learn from it; OK so I created this template named Template:TurkishTOC so that links can be easily included on every page to the previous, next, and all other pages. Just add the text at the top of each page (or wherever) for a full TOC that looks like this:

Or add the text at the bottom for a condensed TOC that looks like this:

I guess the table of contents will need to be updated if changes are made to page titles, or if new pages are added, etc. That can be done by editing the template page directly: Template:TurkishTOC. Of course there might be a better way to do this sort of thing, so if someone knows a better system please show us. I think this is a good project and am looking forward to learning from it :)

--Jay McAliley 02:45, 27 June 2006 (UTC)

Picture of Mount Olympos
Is the actual Mount Olympos in Turkey? If you look at the corresponding wikipedia article, it says it's in mainland Greece.

http://en.wikipedia.org/wiki/Mount_Olympos

 * Yes, it is in Greece...
 * There is also an Olmypos in Turkey

Exercises, anyone?
Merhaba! I'm beginning to learn Turkish as my 5th language and I think this Wikibook needs some exercises at the end of each lesson. I'll begin by adding a few. Brandon Johnsonn 16:58, 2 August 2007 (UTC)

title: Talk:Turkish


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General Astronomy/The Sun

The Sun is the star at the center of the solar system, around which Earth, the seven other planets, and numerous other bodies revolve. It is sometimes called Sol (hence the term "solar system"). The Sun has a mean diameter of 1.392 million kilometers, which is 109.1 times the diameter of Earth and 9.7 times the diameter of the largest planet, Jupiter. The Sun's rotation period relative to the distant stars is 25.05 Earth-days at its equator and 34.3 Earth-days at the poles.

Solar Structure and Composition
The sun is composed of extremely hot, gaseous material. Because of the high temperatures, this material exists in a state called plasma, in which electrons have been stripped from their parent nuclei. The Sun's composition is roughly 90% hydrogen and 10% helium, by total numbers of nuclei. Considering mass, about 71 percent of the Sun is hydrogen, and 27 percent helium. The difference is due to the fact that helium nuclei have about 4 times the mass of hydrogen nuclei (protons). There are small percentages of other elements mixed in.

The Sun is made up of a series of layers, which can be thought of as a set of concentric "shells" from the core outward.

At the center of the Sun is its core, a region of some 15 million kelvin (About 27 million degrees F). The core is where the nuclear fusion reactions that power the Sun take place. Primarily, this is the fusing of hydrogen into helium.

Outside the core is a radiative zone, where energy produced in the core travels toward the surface. However, this energy can only travel outward by radiation for a certain distance, which limits its depth. Temperatures here run from about 7 to 2 megakelvins. An interface region above this is thought to be the source of the solar dynamo which powers the Sun's magnetic field.

Outside the radiation zone and interface region is a convection zone. This zone sits between the heated radiation zone and the cooler outer layers of the Sun. The result of this is a series of motions known as convection. Hot material, being less dense, rises upwards toward the surface; material near the surface, once cooled, becomes denser and sinks downwards again. Through this process, heat is gradually transported upward to the solar surface. The base of the convection zone is at about 2 megakelvins, while material at the very top is at roughly 6000 kelvins.

Atop the convection zone lies the photosphere, the visual "surface" of the Sun from our point of view. Material here is at approximately 6000 K. As a result of the convection going on below, polygonal shapes define the walls of the convection cells, called granules appear all across the surface.

Above the photosphere is the chromosphere, a very diffuse, hot layer. Material here rises in temperature from the 6000 K of the photosphere to about 20,000 K. A transition region above the coronasphere has an even more dramatic rise in temperature, up to a megakelvin.

Finally, outside the chromosphere and transition region is the corona, an extremely tenuous (very low-density) gas over a megakelvin. It is thought that the corona is primarily heated by the magnetic processes of the solar cycle.

Solar Cycles
The Sun goes through regular cycles related to the formation and destruction of its magnetic field every 11 years. This process affects features on the surface of the Sun; it is by observing those features that our knowledge of solar cycles has developed over time.

The Sun's magnetic field is created naturally by the movement of the solar plasma. Because this plasma is made up of charged particles, its movement creates electric fields. Where electric fields are generated, magnetic fields are generated perpendicular to them.

The Sun's rotation, however, is not rigid like the Earth's, because the gaseous material is so much more fluid than the Earth's crust. Material at the equator moves more quickly than does material at the poles; this is called differential rotation. Furthermore, the magnetic field lines are embedded within the plasma, and tend to move with its motions. As a result, the magnetic field lines which initially run from pole to pole become more stretched in the middle, with the center of the line outrunning the pole-anchored ends. Eventually, these lines will wrap around the Sun many times.

As magnetic field lines cannot cross one another, they tend to protrude upwards when they come close to one another, forming "loops" that project out of the solar photosphere. It is along these loops that solar prominences are displayed. The more these lines are wrapped around the Sun, the more "tangled" and disrupted the magnetic field becomes. Eventually, the field is so disrupted that it breaks up completely. After this, of course, a new magnetic field starts to form, and the cycle begins again. The complete process takes about 11 years.

The presence of magnetic fields has an effect on the Sun's photosphere. In discussing solar structure and composition, it was mentioned that the process of convection brings heat from the inner regions of the Sun up to the photosphere. This convection tends to occur in fairly localized zones of rising hot and falling cool material known as convection cells. However, if a magnetic loop is present, it will disrupt one of these convection cells, trapping cool material at the Sun's surface. While these regions (about 4500 K) are only cool compared to the photosphere (at about 6000 K), the overall effect is that they appear dark against the solar "surface". As a result, these are known as sunspots.

The presence of sunspots reflects the cycle of the magnetic fields. In fact, it was the progression of sunspot number and position that gave the first evidence of cycle of magnetic field reversals. At the beginning of the magnetic cycle, when the magnetic field is newly forming, only a few sunspots will appear; this is called a solar minimum. Those sunspots that do appear will tend to be at high solar latitudes - that is, closer to the poles and further from the solar equator. As the cycle continues, sunspots will gradually appear in greater numbers and tend to be closer to the solar equator. The peak of this cycle is known as the solar maximum. After the sunspot numbers peak, they will continue to appear with less frequency, and be still closer to the solar equator. As this cycle trails off, the first few sunspots for the next cycle will start to appear at high solar latitudes, and so forth.

Because they are formed by magnetic field lines, sunspots occur in pairs; at the base of either end of the magnetic loop that formed them. Likewise, the sunspots will have opposite magnetic polarity from one another. There are distinct patterns in the polarities of each pair which can be observed during a cycle. For convenience, we will call the spot that appears to be further along in the direction of the Sun's rotation the "leading" spot, and its partner the "trailing" spot.

Sunspot pairs in the northern solar hemisphere will have opposite polarities from those in the southern solar hemisphere. That is, if the leading spot is polarized one way (call it +) and the trailing spot the other (−) in the northern hemisphere, then in the southern hemisphere the leading spot will be (−) and the trailing spot (+). Sunspot pairs in a given hemisphere will tend to all appear with the same polarities during a solar cycle. However, at the end of the cycle, the polarities will "flip": new sunspots in that hemisphere will have polarities opposite from the previous cycle.

The table below shows the sunspot pattern over four 11-year cycles, for pairs of (leading and trailing) sunspots.

Connection between Sunspot Activity and Aurora on Earth

Aurorae are visible effects of the Sun's activity on the Earth's atmosphere. It results from the interaction of the solar wind, a continuous flow of electrically charged particles—a stream of electrons and protons coming from the Sun—with gases in the upper atmosphere of the earth at altitudes above 50 miles. When these charged particles reach the Earth's magnetic field, they become trapped in it. Bouncing back and forth many of these particles travel toward the Earth's magnetic poles. When the charged particles strike atoms and molecules in the atmosphere, the atmospheric atoms become excited or ionized causing them to emit photons. These photons cause the luminous auroras. The aurora seen in the Northern Hemisphere is called Aurora Borealis or the northern lights whereas the aurora seen in the Southern Hemisphere is called the Aurora Australis.

The collisions of the solar wind with Earth’s upper atmosphere produce electrical discharges which energize atoms of oxygen and nitrogen which subsequently release various colors of light. Mostly aurorae are seen green and red as it is emitted from atomic oxygen. Similarly molecular nitrogen and nitrogen ions produce low red and very high blue/violet aurorae. Whereas ionic nitrogen produces blue and green color aurora and neutral nitrogen produces the red and purple color with the rippled edges. Most auroras occur at about 60 to 620 miles above the Earth. Some extend lengthwise across the sky for thousands of miles or kilometers. A diffuse red aurora occurs above 150 miles. An aurora having a pinkish edge will have an altitude of around 50 to 60 miles.

Auroral activity occurs mostly in a belt called auroral zones, around the geomagnetic poles, between 65 and 70 degrees of geomagnetic latitude. An auroral zone is a ring-shaped region of approximately radius 2500 km around either magnetic pole of the Earth. It was hardly ever seen near that pole itself. At any time of day, the distribution of aurora is slightly different. It's center is offset from the magnetic pole by 3-5 degree night-ward of the magnetic pole. As a result, the auroral arcs reach furthest equator-ward around midnight during a major geomagnetic storm. Auroral zones migrate as close to the equator as 45 to 50 degrees latitude. At higher latitudes in spring and fall, a maximum of aurora activity is noticed as the Earth is at at that time is farthest north or south of the Sun’s equator due to which there is greater chance of Earth intercepting enhancements of the solar wind that emanate from the vicinity of sunspots.

Variation of heights of Aurorae with latitude:-
h’χ – h’ο = H logn sec χ.

where χ = earth-magnetic inclination

h’ο = height of luminosity maximum corresponding to χ = 0

H = (kT)/mg

K= Boltzmann’s constant

T= Absolute temperature

m = mass of gas

g = acceleration of gravity

Aurora occur mostly intensely during the peak phase of the 11-year Sunspot Cycle. Auroral activity also peaks near the maximum of the Sunspot Cycle and for the couple subsequent years. Most violent eruptions on the surface of Sun, called Solar Flares, originate in magnetically active regions around visible Sunspot groupings. Solar Flares release Electrons and Protons which increase the number of Solar particles that interact with the Earth's atmosphere, producing extremely bright Auroras. Sharp variations in the Earth’s magnetic field are called Magnetic Storms and are also the result of Sunspots.

The Earth is surrounded by a magnetic field, called the Magnetosphere that forms a barrier to the solar wind. The solar wind pressure strongly compresses the magnetosphere on the sun-side and draws it out into an extremely long tail on the side opposite. Since the charged particles of the solar wind cannot cross the Earth's magnetic field lines, flow around it. This forms a standing shock wave in space upstream of the Earth, called the Bow Shock. Electrons of the solar wind diffuse into Magnetospheric tail and form a reservoir called the Plasma Sheet. The Magnetosphere and the solar wind form an enormous electrical dynamo where large and complicated electrical currents flow. One component of these currents is carried by the Electrons in the Plasma Sheet, which descends down from 300 km to 100 km following spiral paths along magnetic field lines. These particles then collide with the atmospheric gas causing it to glow, which we call Aurora.

title: General Astronomy/The Sun


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General Astronomy/Earth

Earth's Interior
Based on models of the earth (well supported by the scientific evidence available), the theory of plate tectonics presupposes that the Earth's outermost surface (crust) is made up of two sub-layers, the rigid lithosphere and the semi-molten asthenosphere. Beneath the crust is the mantle, a layer made up of molten rock (magma).

Heat is generated in the Earth's core by uranium, potassium, and thorium.

Plate Tectonics
This map shows all of the Tectonic Plates that make up the Earth's crust Plate tectonics is a theory of geology underlying the observed phenomenon of continental drift.

The rigid stone making up the lithosphere "floats" on the fluid-like asthenosphere, and, in areas where magma wells up from the mantle below the crust, may develop fractures. This results in the lithosphere being separated into contiguous masses of solid earth and rock known as tectonic plates. Due to slow currents in the asthenosphere's material, the plates floating atop this material undergo slow motions in different directions. These floating plates regularly jostle one another, with interactions along these boundaries being responsible for earthquakes and volcanos.

Tectonic plates are roughly divided into two types: continental and oceanic plates. The distinction is based on the thickness of the plates; oceanic plates are thinner than continental plates; as a result, the oceanic plates generally lie below sea level, while the continental plates project above sea level.

The same currents that move tectonic plates with respect to one another also tend to bring molten material closer to the surface at points where a circulation cell is drawing the material upward. In minor cases, this can result in a hot spot, where the material of the plate is eaten away from below, leaving openings for volcanos such as those producing the islands of Hawaii. As plates move over mantle fissures, chains of volcanos can form. In major cases, the rising magma continuously pushes itself into the midst of the plate, eventually cooling to form new plate material. Thus, some tectonic plates are being widened by the addition of new material, via upwelling of magma from below. Currently the Atlantic oceanic plate is in the process of expanding, fuelled by a continuous input of magma along the North Atlantic Ridge. The region of Iceland, which straddles this ridge, is thus gaining territory at a rate of a few centimeters per century.

The boundaries between plates are known as fault lines. Individual faults are regions where two plate sections are moving with respect to one another. Pressure builds up along these regions as the plates are drawn in different directions by the underlying currents; when the pressure is released by the abrupt motion of the plates, an earthquake results. One of the most famous systems of fault lines is the boundary of the Pacific plate, known as the Ring of Fire due to the amount of seismic activity along this boundary. On the easternmost edge of the ring is the San Andreas Fault, on the boundary of the North American and Pacific plates. This fault line is responsible for the earthquake activity in the western United States, most notably the 1906 San Francisco Earthquake.

In some areas one plate will begin to overrun another. The plate being thus overrun will have its edge pressed downward below the leading edge of the other plate. This process, called subduction, results in the edge of this plate being exposed to the greater pressures and temperatures within the asthenosphere, and the rock making it up may begin to liquify. The resulting build-up of magma under pressure may find explosive release through the lithosphere above it, resulting in a volcanic eruption. In addition, the pressure exerted on both plates during a collision may cause the plates to buckle upward some distance from the plate boundaries. The resulting geographical features are known as upthrust mountain ranges. One example of this is the Himalayas in Asia.

The Greenhouse Effect
CO2 (carbon dioxide) is increasing drastically due to burning fossil fuels and deforestation. This gas, among others, traps heat from the sun, making the Earth hotter.  The greenhouse effect is the process by which radiation from a planet's atmosphere warms the planet's surface to a temperature above what it would be without this atmosphere. The intensity of the downward radiation – that is, the strength of the greenhouse effect – will depend on the atmosphere's temperature and on the amount of greenhouse gases that the atmosphere contains.

Earth’s natural greenhouse effect is critical to supporting life, and initially was a precursor to life moving out of the ocean onto land. Human activities, however, mainly the burning of fossil fuels and clearcutting of forests, have accelerated the greenhouse effect and caused global warming. The planet Venus experienced runaway greenhouse effect, resulting in an atmosphere comprised of 96% carbon dioxide, with surface atmospheric pressure roughly the same as found 900 m (3,000 ft) underwater on Earth. Venus may have had water oceans, but they would have boiled off as the mean surface temperature rose to 735 K (462 °C; 863 °F).

title: General Astronomy/Earth


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General Astronomy/The Planets

What qualifies as a planet has a somewhat variable definition, but in general, it should have the following properties:

 * 1) It does not generate energy through fusion
 * 2) It orbits around the Sun (or another star)
 * 3) It is large enough that its self-gravity makes it spherical

To distinguish planets from the masses known as brown dwarfs, one might add a fourth condition: it formed by accretion rather than direct collapse from a nebula.

Planets have been classified in many ways. Perhaps the best physical classification actually uses four categories, each named after a 'typical' planet of the type: Terrestrial, Jovian, Neptunian and Plutonian.

Terrestrial planets have solid (rocky) surfaces, atmospheres that are thin in comparison to their diameters, and rocky interiors. They tend to have comparatively small masses. These include Mercury, Venus, Earth and Mars; Earth's Moon can be seen as a similar type of body.

Gas giants have thick atmospheres of gaseous hydrogen, metallic hydrogen mantles, and rocky cores. They have large masses. These include Jupiter and Saturn. They should, however be distinguished from the ice giants.

Ice giants planets have moderate hydrogen atmospheres, liquid (mostly water) mantles, and rocky cores. Their masses are intermediate. These include Uranus and Neptune. The Neptunian and Jovian planets are sometimes referred to as the "gas giant" planets, but the difference in interiors merits a separate classification.

Plutonian planets have icy surfaces, very thin atmospheres, and rocky interiors. Technically Pluto is the only such planet in our solar system, but similar bodies include most of the moons of the outer planets, notably Ganymede, Callisto, Europa, Titan, and Triton, as well as Pluto's own moon Charon. Another, more recent addition, is Eris (formerly known as 2003 UB313).

title: General Astronomy/The Planets