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Mercury is the innermost and smallest planet in the solar system, orbiting the Sun once every 88 days. It ranges in brightness from about −2.0 to 5.5 in apparent magnitude, but is not easily seen as its greatest angular separation from the Sun (greatest elongation) is only 28.3°. It can only be seen in morning or evening twilight. Comparatively little is known about the planet: the only spacecraft to approach Mercury was Mariner 10 from 1974 to 1975, which mapped only 40%–45% of the planet’s surface. Physically, Mercury is similar in appearance to the Moon as it is heavily cratered. It has no natural satellites and no substantial atmosphere. The planet has a large iron core which generates a magnetic field about 0.1% as strong as that of the Earth[1]. Surface temperatures on Mercury range from about 90 to 700 K (−180 to 430°C, −292 to 806°F), with the subsolar point being the hottest and the bottoms of craters near the poles being the coldest. The Romans named the planet after the fleet-footed messenger god Mercury, probably for its fast apparent motion in the twilight sky. The astronomical symbol for Mercury, displayed at the top of the infobox, is a stylized version of the god’s head and winged hat atop his caduceus, an ancient astrological symbol. The Greeks called it Στίλβων Stilbon (“the gleaming”) and Hermaon. Before the 5th century BC, Greek astronomers believed the planet to be two separate objects: one visible only at sunrise, the other only at sunset. In India, the planet was named Budha (बुध), after the son of Chandra (the Moon). The Chinese, Korean, Japanese, and Vietnamese cultures refer to the planet as the water star , based on the Five Elements. The Hebrews named it Kokhav Hamah (כוכב חמה), “the star of the hot one” (“the hot one” being the Sun). Mercury is smaller than several of the natural satellites or moons in our solar system. MERCURY - is the closest planet to the Sun and so is also the fastest moving (that gravity!), orbiting our star four times faster than the Earth. Because it is so close to the Sun the intense heat doesn't allow any atmosphere to exist, so the daytime temperatures can reach 400°C whilst at night the thermometer plunges to -170°C. Diameter: 4,878 kilometres Distance from the Sun: 57.9 million kilometres Orbits the Sun in (one Mercurian year): 88 days Rotates in (one day): 58 days 15 hours 30 minutes Rank: 2nd smallest planet - 8th in size Looks: Like the Moon - lots of craters OBSERVING MERCURY: Mercury is quite a small planet and the word 'elusive' is often used in terms of trying to find it. This is because it stays close to the Sun and so it never appears far above the horizon. Even some astronomers have not seen Mercury!, but if you know where and exactly when to look, Mercury can be fairly easily found. A small telescope will show the phases, but not any details on Mercury's scorching surface. Due to it's tilted orbit the best times to see Mercury are the evening skies of spring or the morning skies during autumn.

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โˆ™ 2009-01-13 03:45:49
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Q: What is the planet Mercury?
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