The solar system has eight planets,each moves around the sun in an orbit of its own. The orbits of these planets have a shape approximating to a perfect circle, and are located almost on the same plane, called the ecliptic.

In fact, these orbits are elliptical: a little flattened from one side and extended to others.

## The orbits of the inner planets smaller

Mercury, Venus, Earth and Mars are in the groupthe so-called smaller inner planets, or terrestrial planets: they are small, solid, composed of silicates and metals are closest to the sun. Mercury has one of the most elongated orbits, the least similar to the shape of a circle. Its eccentricity - a numerical expression of the deviation from the circle - is 0.205. The orbit of Mercury is almost 58 million kilometers from the sun. On the plane of the ecliptic, it also is uneven, at an angle of 7 degrees.

The planet orbits at a speed of 48 kilometers per second, making a revolution around the sun for 88 days.

The orbit of Venus is very similar in shape to a circle, inUnlike Mercury (eccentricity is equal to 0.0068). The inclination to the ecliptic plane she is also very small: about 3.4 degrees. Planet turns at a speed of 35 kilometers per second, making a complete rotation every 225 days.

The orbit of the Earth's elliptical, its length - more than 930 million kilometers. planet orbital velocity is not constant: it is minimal in July and maximum in February.

Mars is 55 million kilometers from Earthand 400 million kilometers from the sun. Its orbit has the shape of an ellipse is very pronounced, but not so much elongated as those of Mercury, with an eccentricity of 0.0934 in. She is inclined to the ecliptic plane by 1.85 degrees.

## The orbits of the gas giants

The other four planets in the solar system -Jupiter, Saturn, Uranus and Neptune - are called gas giants, or outer planets. Ellipse eccentricity of the orbit of Jupiter is about 0.0488, so the difference between the closest and furthest distance from the Sun is about 76 million kilometers.

Jupiter is the fastest spinning around its axis compared to the other planets of the solar system and the Sun it makes a complete revolution in nearly 12 years.

The orbit of Saturn slightly more elongated than thatJupiter (eccentricity of 0.056), due to which the difference in distance from the Sun is as much as 162 million kilometers. Saturn is moving at a slow speed - about 9.7 kilometers per second. Uranus orbit nearly circular, but with slight variations to the shape of an ellipse. The discrepancies in the calculations between the expected and observed orbit suggested in the middle of the XIX century, that of Uranus is another planet.

Neptune has a small eccentricity - 0,011. Its orbit is so long that a full turn it makes for 165 years - so much time has passed since the discovery of the planet.