Phobos passage from Mars

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Phobos passage from Mars captured by the Mars Rover Opportunity on March 10, 2004

A passage of the Martian moon Phobos in front of the sun , as seen from Mars , occurs when Phobos passes directly between the sun and a point on the surface of Mars. For an observer on Mars, a large part of the solar disk is covered because Phobos has a very low orbit. During such passages, Phobos could be seen with a solar filter as an irregularly large black disc that quickly moves across the blindingly bright sun.

The event can be understood as a partial eclipse of the sun by Phobos. From an orbit , the penumbra of Phobos can be observed as it moves rapidly across the surface of Mars. Mars probes were able to photograph this shadow on many occasions. For a location on Mars, a Phobos passage only takes about 30 seconds because of the short orbit period of 7.6 hours.

Because the orbit of Phobos deviates only slightly from the equatorial plane of Mars, but this is inclined by 25.2 ° (similar to Earth) to the orbit plane of the planet, the shadow of Phobos is spread over different areas of Mars over the course of a year projected. For any given areographic latitude on the surface of Mars between 70.4 ° N and 70.4 ° S there are two points in time in the Martian year at which the shadow of Phobos crosses the corresponding parallel. During this time, half a dozen passes of Phobos take place in this latitude zone. The moon's shadow falls on the northern and southern hemisphere in their respective “winter half-year”, while the equinox in spring and autumn crosses the equator. The passages of Phobos in the northern hemisphere occur roughly symmetrically around the winter solstice .

In the equatorial regions, the transits take place around the equinoxes in spring and autumn, but far from the equator, closer to the winter solstice. On the surface of Mars in general there are passages of Phobos on most days of the Martian year. However, on some days in the Martian year, the shadow of Phobos misses the Martian surface in the north or south. Because it orbits so closely to Mars, Phobos cannot be seen north of 70.4 ° N or south of 70.4 ° S. Observers at high latitudes see a noticeably smaller Phobos because it is further away from them than from the equator. As a result, passageways from Phobos cover the solar disk to a lesser extent for such observers .

Passages in our solar system
Venus	earth	Mars	Jupiter	Saturn	Uranus	Neptune
Mercury	Mercury	Mercury	Mercury	Mercury	Mercury	Mercury
	Venus	Venus	Venus	Venus	Venus	Venus
		earth	earth	earth	earth	earth
			Mars	Mars	Mars	Mars
				Jupiter	Jupiter	Jupiter
	moon	Deimos			Saturn	Saturn
		Phobos				Uranus