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Mercury

Orbital Data:

Semimajor Axis 57,910,000 km, 35,980,000 m, 0.3871 a.u.
Orbit Eccentricity 0.2056
Orbit Inclination 7.004 degrees, 7 deg 0 ' 26 "
Sidereal Period 87.969 days, 0.61515 years
Synodic Period 115.88 days

Planetary Information:

Diameter 4,878 km, 3,031 m, 0.3824 x Earth
Mass 0.0553 x Earth
Density 5.43 g/cm^3
Gravity 0.284 x Earth
Escape Velocity 4.3 km/s
Siderial Rotation Period 58.65 days
Axial Tilt 0.0 degrees

History: Mercury, being the innermost of the planets, is also the fastest in revolving around the sun. For this reason, the ancients named Mercury after the Roman god who served as a messenger for the gods. He is often depicted wearing a winged cap or sandals. It is also associated in medieval alchemy with quicksilver, another name for mercury, one of the seven known metals to the ancients.

Description: Mercury, one of only four terrestrial planets, is the second smallest in both size and mass. It has little to no atmosphere, only consisting of particles collected by the solar wind. Mercury has a strong magnetic field, almost matching the intensity of the one found on earth. Its surface resmbles that of the moon, heavily cratered by meteorite impacts, with a few vast lava seas and small mountain ranges. Because of the similarities between Mercury's day length and year length, it experiences days that are nearly two-thirds of its year. For this reason, and because it has no atmosphere to radiate heat around the planet, the temperature on the side facing the sun averages 400 degrees celcius (700 degrees farenheight), while the side facing away from the sun averages around -170 degrees celcius (-274 degrees farenheight).

Observation: Because Mercury's orbit is so eccentric, its greatest elongation varies from 16 to 27 degrees. For this reason, the planet never rises or sets very far from the sun and thus is only visible during twilight, around sunrise or sunset. With such a short synodic period, Mercury completes a cycle of positions about three times a year. Mercury is invisible during inferior conjunction because of its proximity to the sun, but this is also the point at which the planet is closest to earth. The best time to view the planet is at greatest western elongation, in the morning, or at greatest eastern elongation, in the evening. At this time it is in a half-full phase and is brightest at a magnitude of about 0. Because of Mercury's orbit is so eccentric, the interval between elongations and conjunctions varies usually from two to four weeks.

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