What is a 'planet'?

This applies, in particular, to the designation "planets". The word "planet" originally described "wanderers" that were known only as moving lights in the sky. Recent discoveries lead us to create a new definition, which we can make using currently available scientific information.

Why is it important to define a planet?

Defining the term planet is important, because such definitions reflect our understanding of the origins, architecture, and evolution of our solar system. Over historical time, objects categorized as planets have changed. The ancient Greeks counted the Earth's Moon and Sun as planets along with Mercury, Venus, Mars, Jupiter, and Saturn.

What does the IAU say about planets and other bodies?

The IAU therefore resolves that planets and other bodies, except satellites, in our Solar System be defined into three distinct categories in the following way:

What is a planet in astrology?

Planets are among the many worlds and smaller objects that orbit the Sun. The formal definition of planet, as voted on by the International Astronomical Union in 2006, is as follows: A planet is a celestial body that has cleared the neighbourhood around its orbit.

Which dwarf planets are recognized by the IAU?

Eris, Ceres, Pluto, and two more recently discovered KBOs named Haumea and Makemake, are the dwarf planets recognized by the IAU. There may be another 100 dwarf planets in the solar system and hundreds more in and just outside the Kuiper Belt. Here is the text of the IAU’s Resolution B5: Definition of a Planet in the Solar System:

What planets have life on it?

The place we call home, Earth is the third rock from the sun and the only planet with known life on it - and lots of it too! The red planet is dusty, cold world with a thin atmosphere and is home to four NASA robots. Jupiter is a massive planet, twice the size of all other planets combined, and has a centuries-old storm that is bigger than Earth.