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    Re: Amazing Picture
    From: Dave Walden
    Date: 2012 Aug 20, 08:00 -0700

    Lunars (?) on Mars. Phobos is very fast moving. Would make a good clock. (How good?) We just need some pictures, and Greg could go to work.

    From wiki:

    Name
    Dia (km) ) Orbital period (h) Average moonrise period (h, d)

    Mars I Phobos

    22.2 km 7.66 11.12 h (0.463 d)


    Mars II Deimos

    12.6 km 30.35 131 h (5.44 d)


    If viewed from the surface of Mars near its equator, full Phobos looks about one third as big as the Earth's full moon from Earth. It has an angular diameter of between 8' (rising) and 12' (overhead). It would look smaller when the observer is further away from the Martian equator, and is completely invisible (always beyond the horizon) from Mars' polar ice caps. Deimos looks more like a bright star or planet for an observer on Mars, only slightly bigger than Venus looks from Earth; it has an angular diameter of about 2'. The Sun's angular diameter as seen from Mars, by contrast, is about 21'. Thus there are no total solar eclipses on Mars, as the moons are far too small to completely cover the Sun. On the other hand, total lunar eclipses of Phobos are very common, happening almost every night.[12]

    The motions of Phobos and Deimos would appear very different from that of our own Moon. Speedy Phobos rises in the west, sets in the east, and rises again in just eleven hours, while Deimos, being only just outside synchronous orbit, rises as expected in the east but very slowly. Despite its 30 hour orbit, it takes 2.7 days to set in the west as it slowly falls behind the rotation of Mars, and has long again to rise.
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