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Moons (satellites)
Moons (satellites)
Astronomers call any small body that orbits a planet a satellite.
The Moon is a very large satellite “captured” by the Earth’s gravity. Most other planets have much smaller satellites, or moons.
The outer planets have so many satellites they are called swarms. The four largest satellites that orbit Jupiter are each the size of our Moon. The largest moon orbiting Saturn (called Titan) is bigger than the planet Mercury and even has its own atmosphere. (See also: Shepherd moon.)
(For more individual moons see: Adrastra; Ariel; Callisto; Deimos; Dione; Europa; Ganymede; Helene; Hyperion; Iapetus; Io; Janus; Miranda; Phobos; Triton.)
Morning star
(See: Venus.) N
NASA
The National Aeronautics and Space Administration is a United States government agency founded in 1958 to focus research on aircraft and space. It is more famous for its space flights. Its headquarters are in Washington, D.C., but it has many facilities around the country, including
the Jet Propulsion Laboratory, Kennedy Space Center, and the Goddard Space Flight Center.
Nebula, nebulae
A diffuse mass of interstellar dust and gas (see: Stellar).
 Nebula, nebulae—The Ant Nebula (Menzel 3). This is a picture of fiery lobes spreading out from a dying, sunlike star. This may be what our Sun will look like in its dying stages too.
Neptune
Neptune (diameter 49,500km) is the eighth planet and the farthest of the gas giants from the Sun, orbiting at 4.4 billion km from it, with a rotation of 165 years and a spin of 16 hours.
It is about 17 times the mass of the Earth. Like Uranus, Neptune’s atmosphere is made of hydrogen and helium. Because it has a large magnetic field, it is thought the planet has a molten rocky core. The surface is very cold, -220°C, yet it would be even colder if there were not a source of heat from the core. A system of dust rings surrounds the planet.
The surface atmosphere has dark rings and spots like those on
Rock
Gas
 Neptune—Neptune has a very thick hydrogen-helium atmosphere, then a liquid “mantle” of water, helium, and hydrogen, and possibly a molten rocky core.
Jupiter. One prominent feature for many years was the Great Dark Spot.
(See also: Triton and Voyager)
 Nebula, nebulae—The Laguna Nebula.
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