Post by Chicago Astronomer - Astro Joe on Feb 21, 2006 1:31:48 GMT -6
The Shadow of Phobos
NASA]
Fri, 17 Feb 2006 - Mars' moon Phobos casts its shadow across the surface of the Red Planet in this photograph captured by ESA's Mars Express. Phobos is only 27 kilometres by 22 kilometres in size (17 x 14 miles), and it orbits Mars once every 7.5 hours. To an observer on the ground, this eclipse would look similar to one on Earth; however, Phobos would only cover about 20% of the Sun's surface. And it would be over quickly - the shadow moves at 7200 km/h (4400 mph).
This image, taken by the High Resolution Stereo Camera (HRSC) on board ESA's Mars Express spacecraft, shows the fast-moving shadow of the moon Phobos as it moved across the Martian surface.
The HRSC obtained this unique image during orbit 2345 on 10 November 2005. These observations would not have been possible without the close co-operation between the camera team at the Institute of Planetary Research at DLR and the ESA teams, in particular the mission engineers at ESA's European Space Operations Centre (ESOC) in Darmstadt, Germany.
The shadow of Phobos has an elliptical shape on the Martian surface, because the shadow's cone hits the surface at an oblique angle. This shadow appears to be distorted even more because of the imaging technique of the HRSC.
The shadow moves across the surface with a speed of roughly 7200 kilometres per hour from west to east. The spacecraft travels with a higher speed of about 12 600 kilometres per hour on its almost polar orbit from south to north.
Another phenomenon, that the shadow is darker at its centre than the edges, can be explained by again imagining the observer on Mars. With its small size, Phobos would only cover some 20% of the solar disk.
Even if the observer stood in the centre of the shadow, they would still be illuminated by the uncovered part of the Sun's disk, in a partial solar eclipse instead of a total eclipse.
Full story here from Universe Today: www.universetoday.com/am/publish/mars_light_shadow.html?1722006
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I think that this is quite a cool image... ;D
