File talk:Phobos & Deimos full.gif

Apparent rotation direction of Phobos and Deimos around Mars, relative to stars

This animated image does not show what at first look you might think it shows : Phobos and Deimos moving at different speed over a dark sky with only a few fixed stars. At least this is what i thought for a few seconds… until I remind that these two moons turn, relatively of Mars ground point of view, in opposite directions ! Let me argue about this. Phobos turns around Mars and makes a revolution in 7.7 hours, therefore 0.32 sol (values given in the table from Moons of Mars page). Deimos does it in 1.3 sols. And said "fixed" stars do it in more or less 1 sol. Therefore, relatively to stars, from a surface martian point of view, Phobos goes faster than the stars, and Deimos slower : Phobos turns from West to East, while Deimos from East to West. So how is it possible to see them going in the same rotating direction, as shown on this GIF ? My interpretation is that the fix white spots are NOT stars, but dead pixels, and Spirit camera was not following the stars, and also it is not looking in a fix direction relatively to Mars surface. The stars are too faint to be clearly seen, but if you try to look at the dark sky, you'll notice some spotty background, which is also moving relatively to the fix dead pixels, and that seem to go in a intermediate speed between Phobos and Deimos. Which therefore does solve, at least qualitatively, the puzzle. Do you agree with this? --Eric.LEWIN (talk) 20:47, 6 August 2013 (UTC) (typos correction 25 oct 2015)