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Etymology

The word moon is Germanic in origin, related to mensis (Latin) and menas (ancient Greek), both meaning month.

Definition

Definition of moon : a natural satellite; a celestial body that orbits a planet, or smaller body, which is called the primary. The word moon is used to identify non-artificial satellites of planets, dwarf planets, and minor planets.

Population

Around 344 bodies in the Solar System have been formally classified as moons. Of these, 173 orbit six of the eight planets; 9 orbit the dwarf planets; 104 are asteroid moons; and 58 are moons of bodies located beyond Neptune, in the outer boundaries of the Solar System.

Interesting Facts

  • Pluto's principal moon, Charon, is twenty times closer to its primary than our Moon is to Earth.
  • Psamathe and Neso, two of Neptune's fourteen moons, have the largest orbits of any natural satellites so far discovered in the Solar System. Their orbit around Neptune takes 25 years, on a path that is roughly 125 times greater than the Earth to Moon distance (i.e. 384,400 km, or 238,900 miles, x 125).
  • Jupiter's moon, Io, has hundreds of active volcanoes and is the most volcanically active body in the Solar System.
  • Saturn's largest moon, Titan, is the only moon in the Solar System with a dense atmosphere.
    Saturn's moon Enceladus has an underground ocean, and geysers which eject plumes of water crystals into space.
    To see photos of Saturn and some of its many moons, click here.
  • To see the current phase of the Moon, click here.
MOONS IN OUR SOLAR SYSTEM

Moons per Planet

Largest Moons

Planet

Number

Name

Diameter km

Planet

Mercury

0

Ganymede

5,268

Jupiter

Venus

0

Titan

5,151

Saturn

Earth

1

Callisto

4,821

Jupiter

Mars

2

Io

3,643

Jupiter

Jupiter

67

The Moon

3,475

Earth

Saturn

62

Europa

3,122

Jupiter

Uranus

27

Triton

2,707

Neptune

Neptune

14

Titania

1,578

Uranus

Dwarf Planet

 

Rhea

1,529

Saturn

Ceres

0

Oberon

1,523

Uranus

Pluto

5

Iapetus

1,469

Saturn

Haumea

2

Charon

1,186

Pluto

Makemake

1

Umbriel

1,169

Uranus

Eris

1

Ariel

1,158

Saturn

Total

182

Dione

1,125

Saturn

   

Tethys

1,073

Saturn

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