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Mercury Mercury is unique in that you can see all the planets when looking away from the Sun. The differences in the appearance of the outer planets are minor, but the inner solar system is different. Mars would get the worst part of the deal. It shines at 0.2 magnitude to -0.6 magnitude at opposition. This is a far cry from the best performance visible at Earth: -3.0 mag. Still at conjunction with the Sun, Mars is better: 1.2 mag rather than 1.8 mag at worst from Earth. Earth would be a wondrous site. During opposition it ranges from -4.5 to -5.2 magnitude (at worst -2.9). The Moon would be interesting as well. It beats out Mars and Saturn in brightness most of the time. At opposition the Moon is 0.2 to -0.6 magnitude (1.2 at worst). The separation of the Earth and Moon would range from 6 arcminutes to 17 arcminutes (about a fifth to a half of the Moon's diameter as seen from the Earth. Venus from Mercury would likely overwhelm. From the dark, atmosphereless skies of Mercury, Venus is seen in its full glory -- fully lit when closest. At opposition it can range from an incredible -6.8 to -7.9 magnitude. Only at worst does Venus shine normally -- at -4.6 magnitude. Also notice that the opposition can vary 1.1 magnitude. This is from Mercury's orbit being highly eccentric causing Mercury to be much closer to Venus at some oppositions compared to others. Shortest year of any planet -- 86.969 Earth days. Moonlike, closest to the sun. Longest solar day -- 175.938 Earth-days long. A solar day is defined as the time it takes the Sun to make a complete loop around the sky of a planet or moon. A Mercury solar day is equal to two Mercury years! This is caused by the sidereal day on Mercury being 2/3 the length of its year. A sidereal day is the time it takes for a planet or moon to make a complete turn. Mercury turns so slowly that you can keep up with its rotation by walking a normal pace (3 km/h) at its equator. Greatest range of temperatures. It can range from approximately 100K (-173°C) to 700K (427°C), a temperature range of 600 K or 600°C. Most elusive naked-eye planet you can see in the sky. However when it can be seen, it can rival or possibly appear brighter than Sirius, the brightest star in the sky. Sirius is -1.46 magnitude and Mercury can be as bright as -2.2 magnitude. Mercury will never, however, seem that bright since it is always bathed in Earth's twilight sky. Shortest synodic period as seen from the Earth -- 115.88 days. Synodic period is the time between two oppositions. For distant planets that move slowly, the synodic period is closely equal to a sidereal year; for nearer planets the synodic period is longer. Inside Earth's orbit synodic period starts out long and gets shorter the closer you get to the Sun. Lowest albedo of any planet -- 0.1. The lower the albedo the less light an object can reflect, and hence the darker the surface. A reading of 0 means the object is completely black; a reading of 1 means the object reflects all light. Lowest known atmospheric pressure. It is not much thicker than the surrounding vacuum. |