posted Wed 14 Mar 2012 04:58 AM                     

Mercury is the innermost and smallest planet in the Solar System,[a] orbiting the Sun once every 87.969 Earth days. The orbit of Mercury has the highest eccentricity of all the Solar System planets, and it has the smallest axial tilt. It completes three rotations about its axis for every two orbits. The perihelion of Mercury's orbit precesses around the Sun at an excess of 43 arcseconds per century, a phenomenon that was explained in the 20th century by Albert Einstein's General Theory of Relativity.[12] Mercury is bright when viewed from Earth, ranging from −2.3 to 5.7 in apparent magnitude, but is not easily seen as its greatest angular separation from the Sun is only 28.3°. Since Mercury is normally lost in the glare of the Sun, unless there is a solar eclipse it can be viewed only for short intervals before sunrise when it is near its maximum western elongation, or after sunset when near its maximum eastern elongation. At relatively high latitudes such as those of many European and North American population centres, it is even then near the horizon and obscured in a relatively bright twilit sky. However, at tropical and subtropical latitudes, Mercury is more easily seen because of two effects. (i) the Sun ascends above the horizon more steeply at sunrise and descends

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