Astronomical symbol: ♀
Mercury is the smallest planet among the eight planets, 1/3 larger than the moon. It is also the planet closest to the sun. Mercury's visual magnitude ranges from 0.4 to 5.5; Mercury is so close to the Sun that it is often swamped by intense sunlight, so telescopes rarely allow careful observation of it. Mercury has no natural satellites. Satellites that have passed close to Mercury include the US probe Mariner 10 and the US-launched MESSENGER probe. When Mariner 10 explored Mercury from 1974 to 1975, it only photographed about 45% of its surface. MESSENGER passed by Mercury in January 2008. Mercury is the fastest moving planet in the solar system. The English name of Mercury comes from the Roman god Mercury (Hermes). He is a messenger in Roman mythology. Because Mercury orbits the sun in about 88 days, it is the fastest rotating planet in the solar system. The symbol is a circle on the top, a short intersecting vertical line and a semicircle (Unicode) below. It is the shape of the wand held by Mercury. In the 5th century BC, Mercury was actually considered two different planets because it alternated between appearing on either side of the Sun. When it appeared in the evening it was called Mercury; but when it appeared in the morning it was called Apollo in honor of the sun god Apollo. Pythagoras later pointed out that they were actually the same planet.