Basic Astronomy

Solar System

Solar System
(Solar system with its planets and dwarf planets. Sizes of the planets are to scale, but relative distances are not.)

Solar System consist of Sun and its planetary system. All astronomical objects, which are bound by gravity of Sun is part of Solar system.

There are eight planets, many dwarf planets and their moon(s), asteroid belt, a large number of small bodies (the comets and asteroids) and interplanetary dust. The four inner planets Mercury, Venus, Earth and Mars are comparatively smaller in size and the terrestrial planets. They are primarily composed of metal and rocks. The four outer planets, Jupiter, Saturn, Uranus and Neptune are more massive than the terrestrials and are called gas giants. Jupiter and Saturn are two largest planets and are mainly composed of hydrogen and helium. Uranus and Neptune are two outermost planets and are composed largely of ices, such as water, methane and ammonia. They are known as ice giants.

Solar system was formed approximately 4.6 billion years ago from the collapse of a giant molecular cloud.

All planets in solar system move around Sun in a elliptical orbit with Sun at one focus. All planets orbit, except Mercury, are very nearly circular. All planets orbits are more or less in the same plane (called elliptic plane). The ecliptic plane is inclined with 7 degrees from the the Sun's equator plane.

Name Equatorial
to Sun's
No. of
Mercury 0.382 0.06 0.39 0.24 3.38 0.206 58.64 0
Venus 0.949 0.82 0.72 0.62 3.86 0.007 243.02 0
Earth 1.00 1.00 1.00 1.00 7.25 0.017 1.00 1
Mars 0.532 0.11 1.52 1.88 5.65 0.093 1.03 2
Jupiter 11.209 317.8 5.20 11.86 6.09 0.048 0.41 64
Saturn 9.449 95.2 9.54 29.46 5.51 0.054 0.43 62
Uranus 4.007 14.6 19.22 84.01 6.48 0.047 -0.72 27
Neptune 3.883 17.2 30.06 164.8 6.43 0.009 0.67 13

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