Planets and Moons

Planets

• The current definition of a planet is an object that:

• Orbits the sun.

• Has a spherical shape, due to the gravity resulting from its large size.

• Has no objects of a similar size near its orbit.

• The definition of a planet has been hotly debated in astronomy and certain objects that were previously called planets are no longer called planets.

• For example, in 2006 the International Astronomical Union changed the status of Pluto from ‘planet’ to ‘dwarf planet’ as it didn’t meet the third criterion above.

A planet is a spherical body that orbits the sun and has no objects of a similar size near its orbit.

(Image: Artsiom P, Adobe Stock)

Moons

• A moon is a celestial body that orbits around a planet. This includes the eight major planets as well as dwarf planets, such as Pluto.

• Currently there are hundreds of known moons in our solar system. However, there is no official agreement on what size an object has to be to be classified as a moon, so there is no official total number of moons, and new moons are being discovered each year.

• The inner planets have few or no moons.

• Mercury and Venus have no moons.

• Earth has one moon.

• Mars has two moons.

• The outer planets have many moons. As of 2023:

• Jupiter has 95 moons.

• Saturn has 83 moons.

• Uranus has 27 moons.

• Neptune has 14 moons.

A moon is a body that orbits a planet.

(Image: NASA, Wikimedia Commons)