What is a planet?

The definition of planet has changed several times in the history of astronomy, with the most recent definition being made by the International Astronomical Union (IAU) in 2006.

The IAU's 2006 definition of a planet:

For a celestial body to be considered a planet, it must meet three criteria:

1. It must revolve around the Sun.

2. It must have hydrostatic balance (a round form) thanks to its own gravity.

3. It must have cleared its orbit of other objects. (That is, it must be the dominant object in its orbit.)

With this definition, Pluto, which was previously considered the 9th planet, was removed from planet status and was classified as a "dwarf planet" because it did not meet these criteria. Of course, Pluto was not aware of this.

This decision was taken at the IAU meeting held in Prague, the capital of the Czech Republic, on 24 August 2006.

This reduced the number of planets to 8, and Pluto's new status sparked debate in the scientific world.

It should also be added that the term "extraplanet" has also been accepted for planets that do not revolve around the sun but revolve around their own star.