Dione

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Dione,

in Greek religion and mythology, earth goddess. In some legends she is the daughter of Oceanus and Tethys; in others she is a Titaness, born to Uranus and Gaea. In yet another version she is the mother of Aphrodite. Her name is the feminine form of Zeus. Her cult was associated with the oracle at DodonaDodona
, in Greek religion, the oldest oracle, in inland Epirus, near modern Janina, sacred to Zeus and Dione. According to Herodotus, an old oak tree there became an oracle when a black dove, from Egyptian Thebes, settled on it.
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.

Dione

(dīō`nē), in astronomy, one of the named moons, or natural satellites, of SaturnSaturn,
in astronomy, 6th planet from the sun. Astronomical and Physical Characteristics of Saturn

Saturn's orbit lies between those of Jupiter and Uranus; its mean distance from the sun is c.886 million mi (1.
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. Also known as Saturn IV (or S4), Dione is 695 mi (1,120 km) in diameter, orbits Saturn at a mean distance of 234,500 mi (377,400 km), and has an orbital period of 2.737 earth days—the rotational period is unknown but is assumed to be the same as the orbital period. It was discovered in 1684 by the Italian-French astronomer Gian Domenico CassiniCassini
, name of a family of Italian-French astronomers, four generations of whom were directors of the Paris Observatory. Gian Domenico Cassini, 1625–1712, was born in Italy and distinguished himself while at Bologna by his studies of the sun and planets,
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. Aside from TitanTitan
, in astronomy, the largest of the named moons, or natural satellites, of Saturn. Also known as Saturn VI (or S6), Titan is 3,200 mi (5,150 km) in diameter, orbits Saturn at a mean distance of 759,209 mi (1,221,830 km), and has equal orbital and rotational periods of 15.
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, Dione is the densest of Saturn's satellites; it is believed to be composed primarily of water ice with a considerable fraction of denser material, such as silicate rock. The trailing hemisphere is more heavily cratered than the leading hemisphere, which is the reverse of the cratering on most of the other Saturnian satellites. Another moon, HeleneHelene
, in astronomy, one of the named moons, or natural satellites, of Saturn. Also known as Saturn XII (or S12), Helene is an irregularly shaped (nonspherical) body measuring about 22 mi (36 km) by 20 mi (32 km) by 18 mi (30 km); it orbits Saturn at a mean distance of 234,500
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, is co-orbital with Dione; that is, it orbits Saturn at the same distance as Dione, and precedes Dione by about 60°. Dione also forms a satellite pair with EnceladusEnceladus
, in astronomy, one of the named moons, or natural satellites, of Saturn. Also known as Saturn II (or S2), Enceladus is 310 mi (500 km) in diameter, orbits Saturn at a mean distance of 147,900 mi (238,020 km), and has equal orbital and rotational periods of 1.
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; that is, the two moons interact gravitationally.

Dione

(dÿ-oh -nee) A satellite of Saturn, discovered in 1684 by Giovanni Domenico Cassini. It has a diameter of 1118 km and density of 1.4 g cm–3, and is slightly larger than the satellite Tethys. An important characteristic of Dione is the nonuniformity of its brightness. The trailing hemisphere is dark, with an albedo of approximately 0.3, whereas the brightest features of the leading hemisphere have an albedo of approximately 0.6. Only Iapetus, of the Saturn system, displays a greater variation of brightness between the hemispheres. The surface shows evidence of a number of craters of 30–40 km, with a few large craters 165 km or more in diameter. There are some broad ridges in the southern part of the heavily cratered plains, with a long linear valley more than 500 km in length near the south pole. Dione's relatively high density compared with the neighboring satellites indicates a higher rock content of the interior. The most prominent feature is Amata, a crater 240 km in diameter associated with a system of bright wispy features that extend over the trailing hemisphere. The bright streaks on the surface first imaged by the two Voyager probes have been shown by the Cassini probe to be a vast system of linear features scarring the satellite's surface. A minor satellite, Helene, has been discovered to share the orbit of Dione. See also Table 2, backmatter.

Dione

[′dī·ə‚nē]
(astronomy)
A satellite of Saturn that orbits at a mean distance of 2.35 × 105 miles (3.78 × 105 kilometers) and has a diameter of about 700 miles (1120 kilometers).