Why is there only 8 planets?

Answer 1

For something to be a planet it has to fit under a certain definition

A planet in our Solar System must:

• be in orbit around the Sun
• have sufficient mass to assume hydrostatic equilibrium (a nearly round shape)
• have "cleared the neighbourhood" around its orbit, meaning no large pieces of debris lie in its way

Only eight objects in our solar system fit this description. There used to be nine planets (including Pluto) but since astronomers revised the definition of a planet Pluto does not meet the last requirement and is no longer a true planet. Instead it is classified as dwarf planet.

Answer 2

The ancients only knew about (5 planets + Earth) because to really see the other two you needed a telescope. The planets they knew were:

# Mercury # Venus # (Earth) # Mars # Jupiter # Saturn All these are easily visible to the naked eye and of cause they can be seen to move against the background of the stars (except the Earth because we are on that)

It was in 1718 (290 years ago) that Uranus the 7th planet was discovered by William Herschel using a telescope. Although it is visible to the naked eye like the other six, it was never recognized as a planet by ancient observers due to its dimness and slow orbit. The 8th planet Neptune was found by mathematical prediction rather than regular observation. Unexpected changes in the orbit of Uranus led astronomers to deduce the gravitational perturbation of an unknown planet was the cause and they predicted where to look to find it.

Answer 3

Only 5 planets (besides Earth) were known at that time because they were the easiest to detect, you can see them with the naked eye. Uranus and Neptune can only be seen with a telescope, and you need to know where to look...

Answer 4

In our Solar System there are only 8 planets but there are also Dwarf Planets. Dwarf Planets are not planets because they are too small. Any planet smaller then Mercury is a Dwarf Planet. Dwarf Planets are usually found in the Kuiper Belt or farther away. The first discovered Dwarf Planet was Pluto. Pluto usually has no atmosphere. Pluto is bigger then the other Dwarf Planet Ceres. Pluto use to be called the 9th planet now a Dwarf Planet. Pluto has 3 of its own moons. Charon is about half the size of Pluto. It is Pluto's largest moon and is thought to have broke off Pluto millions of years ago. The other 2 moons are very small. These are Nix and Hydra. They are so small they aren't round! Pluto was named after the Roman god of the underworld. Charon is named after a man who took people to the underworld. Ceres is a large asteroid in the Asteroid Belt. Ceres is also a Dwarf Planet itself. Ceres was named after the Roman goddess of the harvest. Then farther away then Pluto is Eris. Eris is a Dwarf Planet farther away from the sun. It is slightly bigger then Pluto. It has one moon named Dysnomia. It is very small compared to Eris. Eris was named after the Roman god of Spite who caused the Trojan War. There's your answer.

Answer 5

there are many sciencetific reasons for this but the thing it boils down to is that they not have the sciencetific equipment,ie when the first telesope as inveted the same man who invented it was uranus. if you want more deatail i would just search up uraunas and who inventd it,

Answer 6

Ptolemy only knew 5 planets other than the Earth:

1. Mercury
   
2. Venus
   
3. Mars
   
4. Jupiter
   
5. Saturn
   

The reason is that these planets are visible with the naked eye. Also, keep in mind that most people in the ancient world didn't know that the Earth was a planet.

Answer 7

Planets up to Saturn can be seen EASILY with the naked eye; Uranus and Neptune can only be seen in telescopes.

Answer 8

The others were too far away and therefore too faint to be seen with the naked eye.