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| Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune Pluto | |
| Sun |
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Classification
The Sun is an ordinary "G2" star, one of more than 100 billion stars in the Milky Way galaxy. The Sun is a yellow dwarf star, which means it is a medium size star. It is believed to be over 4 billion years old. The Sun is by far the largest object in the solar system. It contains more than 99.8% of the total mass of the Solar System. (Jupiter contains most of the rest). |
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Location
The Sun is the closest star to Earth. It is in the Milky Way galaxy. |
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The Sun in mythology
The Sun is personified in many mythologies: the Greeks called it Helios and the Romans called it Sol. Many ancient peoples worshiped the Sun as a god. They thought a solar eclipse meant the Sun god was angry with them. They believed the Sun god's anger could only be calmed with prayer and sacrifice. |
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Rotation and Revolution
The Sun spins slowly on its axis as it revolves around the galaxy. The outer layers of the Sun exhibit differential rotation: at the equator the surface rotates once every 25.4 days; near the poles it's as much as 36 days. This odd behavior is due to the fact that the Sun is not a solid body like the Earth. Similar effects are seen in the gas planets. The differential rotation extends considerably down into the interior of the Sun, but the core of the Sun rotates as a solid body. |
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Size
The Sun is the most prominent feature in our solar system. It is the largest object and contains approximately 98% of the total solar system mass. It has a diameter of 1,392,000 kilometres. One hundred and nine Earths would be required to fit across the Sun's disk, and its interior could hold over 1.3 million Earths. If the Earth was as big as a golfball, the Sun would be as big as a house.
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| Comparative sizes of the Sun and Earth |
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Composition
The Sun is, at present, about 75% hydrogen and 25% helium; everything else ("metals") amounts to only 0.1%. This changes slowly over time as the Sun converts hydrogen to helium in its core. The Sun is about 4.5 billion years old. Since its birth it has used up about half of the hydrogen in its core. It will continue to radiate "peacefully" for another 5 billion years or so (although its luminosity will approximately double in that time). But eventually it will run out of hydrogen fuel. It will then be forced into radical changes which, though commonplace by stellar standards, will result in the total destruction of the Earth. |
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Surface Conditions
Conditions at the Sun's core are extreme. The temperature is 15.6 million Kelvin (or 15,000,000 degrees Celsius). The core's gases are compressed to a density 150 times that of water. The surface of the Sun, called the photosphere, has a temperature of about 5800 K. Sunspots are cooler regions, only 3800 K (they look dark only by comparison with the surrounding regions). Sunspots can be very large, as much as 50,000 kilmetres in diameter. A small region known as the chromosphere lies above the photosphere. The highly rarified region above the chromosphere, called the corona, extends millions of kilometers into space but is visible only during eclipses. Spectacular loops and prominences are often visible. (See the picture.) Temperatures in the corona are over 1,000,000 K. |
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The Sun's satellites
There are nine planets and a large number of smaller objects orbiting the Sun. |
Special Features
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Resources Used
Starchild Views of the Solar System The Sun Melbourne Planetarium Small Worlds David Drew: Nelson, 1989 The Gas Giants David Drew: Nelson, 1989 |
| Solar System Unit | Classification | Glossary |
| Images from: | Astronomical Pictures & Animations | Astronomy Picture of the Day | Welcome to the Planets |
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