Moon

Cosma / Communication / Knowledge / Realm / Physical / Universe / Planetary System / Moon
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moon : a natural satellite of a planet — Webster See also OneLook

Encyclopedia

Natural satellite or moon is a celestial body that orbits a planet or smaller body, which is called its primary. The two terms are used synonymously for non-artificial satellites of planets, of dwarf planets, and of minor planets. Of the inner planets, Mercury and Venus have no moons; Earth has one large moon, known as the Moon; and Mars has two tiny moons, Phobos and Deimos. The large gas giants have extensive systems of moons, including half a dozen comparable in size to Earth’s moon: the four Galilean moons, Saturn’s Titan, and Neptune’s Triton. Saturn has an additional six mid-sized moons massive enough to have achieved hydrostatic equilibrium, and Uranus has five. The Earth-Moon system is unique in that the ratio of the mass of the Moon to the Earth is much greater than any other planet-moon ratio in the Solar System, and the Moon’s orbit with respect to the Sun is always concave. — Wikipedia

Moons Category (Wikipedia)
Moon, Natural Satellite (Encyclopædia Britannica)

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Science

SciShow (YouTube Channel)

European Space Agency, ESA (YouTube Channel)

Solar System Exploration: Moons (JPL, NASA)
Satellites of Outer Planets (Minor Planet Center, International Astronomical Union)
Natural Satellites (WolframAlpha)

Exomoon or extrasolar moon is a natural satellite that orbits an exoplanet or other non-stellar extrasolar body. It is inferred from the empirical study of natural satellites in the Solar System that they are likely to be common elements of planetary systems. The majority of detected exoplanets are giant planets. In the Solar System, the giant planets have large collections of natural satellites (see Moons of Jupiter, Moons of Saturn, Moons of Uranus and Moons of Neptune). Therefore, it is reasonable to assume that exomoons are equally common. — Wikipedia