Difference between a Moon and a Planet

Updated on April 1, 2017

Among the different astronomical bodies, we are most familiar with the planet Earth and the moon. The Earth is one of the planets in the solar system and the moon is the nearest celestial object to it. Read this article to know more about planets and moons and how these two are differentiated.


The moon orbiting the Earth

A moon is a celestial body that orbits a planet. It also revolves around the sun at the same time that it spins around its host planet. Moons are also referred to as the planets’ natural satellites. They range in sizes and some of these natural satellites are even bigger than some planets. Ganymede (Jupiter’s moon) and Titan (Saturn’s moon) for example, are moons that are bigger than Mercury.

Number of identified moons in the solar system

In the solar system, all the planets have moons except for Mercury and Venus. The planet with the least number of moons is Earth since it only has one. Mars comes next with two moons. Pluto, which is no longer considered a planet, has five moons. Neptune has thirteen moons while Uranus has twenty-seven. Jupiter and Saturn are the planets in the solar system with the most moons, each having fifty-three. These two planets, along with Neptune, still have provisional moons. These are unconfirmed moons which can still increase the three planets’ total moon count.

The Earth’s moon

Among all the known moons in the solar system, the Earth’s moon is the fifth largest natural satellite. It is also identified to be the largest planetary satellite relative to the size of its host planet. The Earth’s moon is called Luna. It is around 238,855 miles (384,400 km) away from the Earth. It was estimated to have taken shape about 4.51 billion years ago from debris formed after the impact between Earth and another planet called Theia.

Planets revolving around the sun

A planet, as defined by the International Astronomical Union (IAU), is a celestial body that revolves around the sun, has enough gravity to maintain a nearly round shape, and is the most massive object along its orbit. Based on the recent definition provided by the IAU, the number of planets in our solar system has been lowered down to eight, namely: Mecury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. They are arranged or usually mentioned in the order corresponding to their distance from the sun. Pluto was once considered a planet but not anymore since it has not cleared its orbit of other neighboring objects.

Some planets in the solar system are visible to the naked eye. In ancient times, planets were regarded as divine. Ancient astrologers believed that the planets symbolized the will of the gods and their impact on earthly occurrences and human behavior. Through the advancement of scientific knowledge, there have been eye-openers and changes in the perception and understanding of the planets. With the improvement of observational tools, astronomers realized that planets rotated around tilted axes, much like the Earth. Moreover, some planets were observed to have ice caps and seasons. Other planets were also noted to have volcanoes, hurricanes, movements in their crust, and water.

Moon vs Planet

What is the difference between a moon and a planet? A moon is a celestial object orbiting a planet while a planet is a celestial object orbiting the sun. Moons are always smaller than their host planet. Planets, on the other hand, are usually larger than moons. However, there are a few exceptions to this since some of the moons of the bigger planets (Jupiter and Saturn) are larger than Mercury.

Comparison Chart

Moon Planet
Celestial object orbiting a planetCelestial object orbiting the sun
Always smaller than its host planetUsually larger than moons