The planets can be classified to two parts the first is the 4 inner planets that are composed from rocks and metals and they are Mercury, Venus, Earth and Mars. The other part is the 4 outer planets which are different in the composition, where Jupiter and Saturn consist of hydrogen and helium, while Uranus and Neptune consists of ices of water, methane and ammonia.
Mercury is the smallest planet on the solar system, it is the nearest planet to the sun, it was first mentioned in the 14th century by an Assyrian astronomer. The Romans were the people that gave it the name.
Venus is the neighbour planet of the earth, it even considered the earth’s sister as they both are alike in their compositions and their gravity. Due to its shinning it has been noticed thousands of years ago. It was mentioned in the year 1032 by the Persian astronomer Avicenna (980-1037), the Romans gave it his name. Galileo Galilei (1564-1642) the famous Italian scientist and astronomer proved that Venus orbits around the sun by his telescope.
Information about our planet Earth has been discovered throughout years, you can find those discoveries in the post Who Discovered The Truth About The Earth? The moon orbits around the Earth, it was first explored by the Russians in the years 1959-1976, but the first man whom walked on the moon was the American Neil Armstrong in the year 1969.
Mars the red planet is the other neighbour of the Earth, it was mentioned by the Babylonians and Egyptians and Greeks, each of them called it a different name but as the other planets the Romans gave it the name that we use now. There are two moons that orbit around Mars, they were discovered in the year 1877 by the American astronomer Asaph Hall (1829-1907).
Between the Inner planets and the Outer planets exists the Asteroid belt which are small planets. Some scientists believe that their number can reach up to 750 thousands planets, along with millions of asteroids. The first to suggest it, was Charles Bonnet (1720-1793) the Swiss naturalist in the year 1766. Giuseppe Piazzi (1746-1826) the Italian priest was the first to notice it in the year 1801. In the year 1802, William Herschel (1738-1822) the German British astronomer called the objects asteroids.
Jupiter is the first planet on the outer planets. It was first noticed in the 7th century by the Babylonians. Jupiter was the first planet to be measured due to the researches of Hippolyte Fizeau (1819-1896) a French physicist who noticed that using an array of small instruments, the diameter of a star can be measured. Then Albert Abraham Michelson (1852-1931) the American physicist used this information in the year 1891 to measure the Jupiter diameter.
Saturn is the second planet in the outer planets, it is distinguished by its rings. It was observed by the naked eye by the ancient Babylonians astronomers, also the ancient Romans gave it its name. Galileo Galilei was the first to notice Saturn’s rings in the year 1610, but he mistaken the rings for two moons. Christiaan Huygens (1629-1695) a Dutch mathematician and astronomer discovered the rings and 4 planets of saturn. There are 62 moons that orbits around Saturn.
Next there is Uranus, that was first thought of as a star, John Flamsteed (1646-1719) the English astronomer was the first to observe the planet in the year 1690, William Herschel assured that fact after he invented his telescope.
Neptune is the last planet on the solar system. Galileo was the first to spot it in the year 1612.
There are also dwarf planets Ceres, Pluto, Haumea, Makemake and Iras.