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Related: About this forumHow do Phobos and Deimos look from Mars?
How do Phobos and Deimos look from Mars?
Feb 26, 2015
by EarthSky in FAQs » Space
http://earthsky.org/space/phobos-and-deimos?utm_source=EarthSky+News&utm_campaign=6effaa842f-EarthSky_News&utm_medium=email&utm_term=0_c643945d79-6effaa842f-393525109
Phobos and Deimos are Mars two tiny moons. They dont look like our moon does, from Earth.
How do the two Martian moons Phobos and Deimos look from the surface of Mars? First of all, they dont look at all like Earths moon does from Earth!
The Martian moons are tiny. The larger moon, Phobos, is only about about 14 miles (23 km) across. And Deimos is about half that size. Plus, these little moons orbit Mars more closely than our moon orbits Earth. But, of course, because theyre so tiny, they appear smaller than our moon does from the surface of their home world.
In fact, Deimos, the more distant moon, looks like a star in Mars sky. But its twice as bright as any starlike object seen in Earths sky. Deimos orbits at nearly the same speed Mars rotates, so it needs three Martian days to crawl from one side of Mars sky to the other. And, by the way, a day on Mars is about the same length as Earths day.
On the other hand, Phobos the larger and closer of the two moons zooms around Mars two and a half times every Martian day. Because it out-races Mars rotation, Phobos rises in the west and sets in the east. Phobos appears about a third as large in the Martian sky as our moon does in Earths sky. Whats more, Phobos isnt round like our moon. It resembles a shining gray-white potato.
Phobos has a nearly circular orbit along Mars equator. It orbits Mars so closely, however, that its apparent size changes for viewers on the equator. Near the horizon Phobos appears smaller as it climbs in the sky, Phobos comes nearer the viewer until its directly overhead. Then it appears larger.
Another odd thing about Phobos its not visible all over Mars. Phobos orbits above Mars equator so near the planet that its always hidden beneath the horizon in the Martian polar regions. Our moon, by contrast, can be viewed anywhere on Earth.
For observers on the Martian equator, Phobos eclipses the sun nearly every day. Eclipses last only about 30 seconds, so quickly does Phobos race across the sky. Because Phobos covers only a fraction of the suns disk, eclipses are never total.
For observers in the north and south mid-latitudes of Mars, Phobos never eclipses the sun it always moves south of the sun (for northern observers) or north of the sun (for southern observers).
Deimos eclipses the sun much less often about once a month. Because its smaller and farther away than Phobos, it would be barely visible against the suns disk.
As seen from Mars, Phobos and Deimos pass through phases, just like Earths moon. They pass from new to crescent to gibbous to full to gibbous to crescent to new again. However, Deimos phases are not terribly obvious they are seen only as a slow change in brightness. Phobos phases are more apparent. Because Phobos is irregular, however, the phases look strange. For example, crescent Phobos looks squashed and jagged.
The surface material of Phobos and Deimos is rich in dark carbon they are among the darkest moons in the solar system. They reflect about 5% of the light that strikes them about half as much as Earths moon. To get a sense of how dark that is, keep in mind that our moon is about as reflective as asphalt. Phobos and Deimos, then, are half as reflective as asphalt. From the surface of Mars, however, the two moons still look bright and gray-white against the black night sky.
More and more pix at link above
SCVDem
(5,103 posts)I love this sciencey stuff!
Thanks for posting it.
alfredo
(60,077 posts)htuttle
(23,738 posts)...somebody had so say it....
Beartracks
(12,821 posts)... by the Death Star.
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Doc Holliday
(719 posts)....and it was long ago and far away.