There are eight main planets in our Solar system. The word planet come from the ancient Greeks and means wandering star. The eight planets starting from the sun are, Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. The four planets closest to the sun are the inner planets, they are mainly made up of mainly of rock and are much denser than the four outer planets. The outer planets are also known as the Gas giants, they tend to be larger and are made up mainly of gases with smaller solid or liquid centres. A good planet mnemonic to help remember the order of the planets from the Sun is “My Very Excellent Mother Just Served Us Nachos”
The definition of a planet was introduced in 2006 by Astronomers of the International Astronomical Union. Before this planets did not have an exact definition.
The three main things that define a planet is, a celestial body which:
1 . Orbits around the sun
2. Is big enough in mass for gravity to compress it into a round shape
3. Has cleared the neighbourhood surrounding its orbit (This is the reason Pluto was changed to Dwarf planet)
Planets that only cover the first two of these are classed as Dwarf planets.
All of the planets except for Earth are named after Greek or Roman Gods & Goddesses. Only three of the planets were officially ‘discovered’ this is because the remaining planets were visible by the unaided eye there for people have been looking at them for years. The three planets that were officially discovered are:
- Uranus By Sir William Herschel in 1781
- Neptune By John Couch Adams in 1846
- Pluto By Clyde Tombaugh in 1930