MSL - Astronomical Observations, Phobos/Deimos, planetary/celestial observations and more |
MSL - Astronomical Observations, Phobos/Deimos, planetary/celestial observations and more |
Jun 29 2013, 05:25 PM
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#31
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Senior Member Group: Members Posts: 4256 Joined: 17-January 05 Member No.: 152 |
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Aug 21 2013, 03:19 AM
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#32
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Senior Member Group: Members Posts: 2346 Joined: 7-December 12 Member No.: 6780 |
"How wide would the shadow be?"
There is no umbra of Phobos on the Martian surface. The size of Phobos is 26,8 × 22,4 × 18,4 km, average 22.2 km, distance from the surface 6,000 km. Diameter of the Sun 1,392,684 km, average distance Sun-Mars 228 million km. Apparent diameter of Phobos relative to Sun therefore (22.2/6,000) / (1.4/228)=0.61. Therefore the antumbra will be about 14.2 km (remaining 39% of Sun's apparent diameter). The whole penumbra adds a tiny bit more than the diameter of Phobos around the antumbra, i.e. 22.2 km, together 14.2 + 2 * 22.2 = 58.6 km. That's a rough approximation based on average values at noon. The eclipse was in the afternoon, so we get a roughly elliptical shadow, with the apparent diameter of Phobos a little smaller. Irregular shape of Phobos is to be added. See also Transit of Phobos from Mars on Wikipedia, Phobos, Sun, Distance Sun-Mars. |
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