​Our Solar system

Our solar system consists of the sun (the star), the eight major planets, their natural satellites (moons), asteroids (space rocks), and ​comets. A star and all the heavenly bodies that orbit around it make a solar system. The sun's gravitational pull keeps these objects in fixed paths called orbits. The nuclear reaction which powers the sun releases an enormous amount of heat and light energy. Planets and their moons shine only because they reflect sunlight.

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​The inner planets (Mercury, Venus, Earth, and Mars) are called terrestrial or earth-like planets while the outer planets (Jupiter, Saturn, Uranus, and Neptune) are gas giants. All planets except Mercury and Venus have natural satellites or the moon. Our earth has only one moon.

​Sun and all the planets originated from a cloud of gas and dust called the solar nebula. This gas cloud or nebula started to collapse and the particles were pulled together by the gravitational force. The central part became the Sun and the rotating cloud around the Sun became a flat disc. Planets were formed from this disc.

​Paths along which the planets revolve around the sun are called their orbits. orbits of most planets in our solar system have the shape of an ellipse (oval).

​The distance between planets and also the distance between the planets and the sun are not very great when compare with the distance between stars. The distances in the solar system are usually measured in a unit called the astronomical unit (AU). One AU is the distance between the earth and the sun, which is approximately 150 million kilometers.

​Distances in outer space, between stars, are so great that the astronomical units are too small. For such measurements, we use another unit, the light-year. This is the distance traveled by a beam of light in a year. Light travels 300,000 km per second in a vacuum. In a year it travels about 9.5 trillion kilometers.