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Astronomy Reference Libraries

Page 15 of about 165 Articles
Mars Moon -- Deimos
2004-10-19 04:45:40

Mars' Moon Deimos -- outermost of two small moons orbiting the planet Mars. Deimos orbits Mars at a distance of about 23,500 km (about 14,100 mi), completing an orbit once every 1.26 Earth days. The moon's orbit is almost circular and is only slightly tilted relative to the Martian equator. Deimos is irregular in shape, measuring about 15 km (about 9 mi) along its longest side and about 11...

Mars Moon -- Phobos
2004-10-19 04:45:40

Mars' Moon Phobos -- in astronomy, innermost moon, or natural satellite, of Mars. Phobos orbits Mars at a distance of only 9,378 km (5,627 mi), closer to its planet than any other moon in the solar system. In fact, it is so close that the force of Mars's gravity is stronger than the force keeping the moon in its orbit, so the radius of Phobos's orbit is decreasing at the rate of about 1.8 m...

Earths Moon
2004-10-19 04:45:40

The Moon -- natural satellite of a planet, in particular, the single natural satellite of the earth. The Earth-Moon System The moon is the earth's nearest neighbor in space. In addition to its proximity, the moon is also exceptional in that it is quite massive compared to the earth itself, the ratio of their masses being far larger than the similar ratios of other natural satellites...

Whirlpool Galaxy M51
2004-10-19 04:45:40

Whirlpool Galaxy -- Discovered 1773 by Charles Messier. The famous Whirlpool galaxy M51 was one of Charles Messier's original discoveries: He discovered it on October 13, 1773, when observing a comet, and described it as a "very faint nebula, without stars" which is difficult to see. Its companion, NGC 5195, was discovered in 1781 by his friend, Pierre Mchain, so that it is mentioned in...

Virgo Cluster of Galaxies
2004-10-19 04:45:40

Virgo Cluster of Galaxies -- This giant agglomeration of galaxies is the nearest big cluster of galaxies, the largest proven structure in our intergalactic neighborhood, and the most remote cosmic objects with a physical connection to our own small group of galaxies, the Local Group, including our Milky Way galaxy. This structure is another discovery by Charles Messier, who noted behind his...

Virgo A Galaxy M87
2004-10-19 04:45:40

Virgo A Galaxy -- Discovered 1781 by Charles Messier. The giant elliptical galaxy M87, also called Virgo A, is one of the most remarkable objects in the sky. It is perhaps the dominant galaxy in the closest big cluster to us, the famous Virgo Cluster of galaxies (sometimes also called "Coma-Virgo cluster" which is more acurate, as it extends into constellation Coma), and lies at the...

Vega
2004-10-19 04:45:40

Vega -- Vega (Alpha Lyrae) is the lead star in the constellation Lyra, reaching near directly overhead the mid-northern latitudes, during the summer. It's a "nearby star" at only 25 light years distant and together with Arcturus and Sirius, one of the brightest stars in the Sun's neighbourhood. Vega is a vertex of the Summer Triangle. Its spectral class is A0V (Sirius, an A1V, is slightly...

Trifid Nebula
2004-10-19 04:45:40

Trifid Nebula -- Discovered by Charles Messier in 1764. Charles Messier discovered this object on June 5, 1764, and described it as a cluster of stars of 8th to 9th magnitude, enveloped in nebulosity. The Trifid Nebula M20 is famous for its three-lobed appearance. This may have caused William Herschel, who normally carefully avoided to number Messier's objects in his catalog, to assign...

Triangulum Galaxy
2004-10-19 04:45:40

Triangulum Galaxy -- The Triangulum Galaxy, Messier object M33, is a spiral galaxy of type Sc located in the constellation Triangulum. Triangulum is small relative to its larger neighbors such as the Milky Way and Andromeda Galaxy, but is about average compared to most spiral galaxies in the universe. Triangulum is a member of the Local Group of galaxies and may be a gravitationally...

Tau Ceti
2004-10-19 04:45:40

Tau Ceti -- Tau Ceti is a star commonly used by science fiction authors since it is similar to the Sun, being of similar mass and similar spectral type as well as being relatively close to us. However, Tau Ceti is a "metal-deficient" star and therefore extremely unlikely to have rocky planets around it. It can be seen with the unaided eye as a faint star in the constellation of Cetus....