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Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto
The solar system, located at the edge of the Milky Way Galaxy, contains various types of celestial bodies: nine planets including Earth, moons, asteroids, comets, dust and gas. All revolve around the Sun, which is in the center of the system and constitutes the bulk of the mass of the entire system. The Sun's huge mass (approximately 350,000 times that of Earth) generates conditions for the creation of thereto-nuclear reactions in its core, which are the source of its heat and light. The rest of the objects in the solar system are dark and relatively cold, and can be seen only due to the light that the Sun reflects off them. The Sun's light and warmth enables the existence of life on Earth.
Most of the planets, except Mercury and Venus have moons consisting mainly of rocks and water ice, measuring no more than several hundred kilometers. However, a number of moons, including Earth's moon, are equal in size to the smaller planets. The giant planets are surrounded by a large number of moons: Jupiter has 70 moons, and Saturn has 50 moons, including Titan - the only moon with an atmosphere.
Our Moon is the farthest place in the Universe astronauts have landed on.
Asteroids - fragments that did not coalesce into a complete planet - are estimated to number in the hundreds of thousands, and are found in the gap between Mars and Jupiter. The diameter of the largest asteroid - Ceres - is about 900 kilometers. The smallest, and most beautiful of the solar system objects, are the comets, which consist of a mixture of water ice, dust and gas, measure only a few kilometers in size. Most of the time they are to be found at the frozen, dark outskirts of the solar system. Once they enter the inner solar system, closer to the heat of the Sun, their ice evaporates, the embedded dust is released, and the result is the impressive tails of these comets, which in historic times inspired fear and panic.
Igal Pat-El
Chairman
Israeli Astronomy Association
