# What Would The Martian Moons Look Like? **URL:** \ **Category:** Factual Questions\ **Created:** [August 10, 2003, 5:27pm UTC](https://boards.straightdope.com/t/what-would-the-martian-moons-look-like/194226 "2003-08-10T17:27:31Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![ralph124c](https://avatars.discourse-cdn.com/v4/letter/r/8797f3/32.png) [@ralph124c](https://boards.straightdope.com/u/ralph124c)\ **Post date:** [August 10, 2003, 5:27pm UTC](https://boards.straightdope.com/t/what-would-the-martian-moons-look-like/194226/1 "2003-08-10T17:27:31Z")
(From the surfaceof Mars). Mars has two moons (Deimos and Phobos)…from my undergrad astronomy course I know that these moons are very small (much smaller than the earth’s moon); however, they are also closer to mars. What appearance would they have in the Martian night sky? Would they cast any appreciable light? Also, have any of the mars landers photographed these moons from the surface? In the old “JOHN CARTER OF MARS” series, the mmons are described to be quite visible at night.😕 ---
**Author:** ![yabob](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/yabob/32/2821_2.png) [@yabob](https://boards.straightdope.com/u/yabob)\ **Post date:** [August 10, 2003, 5:41pm UTC](https://boards.straightdope.com/t/what-would-the-martian-moons-look-like/194226/2 "2003-08-10T17:41:29Z")
Here you go: [http://stardate.org/resources/ssguide/mars\_moons.html](http://stardate.org/resources/ssguide/mars_moons.html) > [@](#): > > Two small moons, Phobos and Deimos, orbit Mars. The larger moon, Phobos, passes across the Martian sky from west to east twice a day. It would look about half as big as the full Moon does on Earth. It’s also so close to Mars that you couldn’t see it from the Martian poles. The next paragraph says that Deimos would be visible as a small dot. It doesn’t mention it, but I would imagine the extreme thinness of the Martian atmosphere would aid the viewing of the smaller satellite. It wouldn’t twinkle, for one thing. ---
**Author:** ![yabob](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/yabob/32/2821_2.png) [@yabob](https://boards.straightdope.com/u/yabob)\ **Post date:** [August 10, 2003, 5:46pm UTC](https://boards.straightdope.com/t/what-would-the-martian-moons-look-like/194226/3 "2003-08-10T17:46:26Z")
Excuse me, I don’t know that it would twinkle anyway. Planets don’t when viewed from earth. ---
**Author:** ![Joe\_Random](https://avatars.discourse-cdn.com/v4/letter/j/e8c25b/32.png) [@Joe\_Random](https://boards.straightdope.com/u/Joe_Random)\ **Post date:** [August 10, 2003, 6:05pm UTC](https://boards.straightdope.com/t/what-would-the-martian-moons-look-like/194226/4 "2003-08-10T18:05:44Z")
> [@](#): > > \*Originally posted by yabob \* > \*\*Excuse me, I don’t know that it would twinkle anyway. Planets don’t when viewed from earth. \*\* That’s not a function of them being planets, but rather a function of them appearing slightly larger in the sky than stars. Also, planets _can_ twinkle under certain atmospheric conditions. > [@](#): > > _From [Ask Discover](http://www.discover.com/ask/main48.html)_ > Most stars are so far away that they appear only as tiny, unresolved points of light. When starlight passes through the various parts of Earths atmosphere—the ionosphere, ozonosphere, thermosphere, mesosphere, stratosphere, and especially the dense troposphere closest to the ground—it is jiggled and wiggled and smudged and smeared by the different light-bending properties within and between the layers. This bending, or refraction, randomly shifts the position of the stars image in the sky by more than the width of the image itself—easy to do because the stars image is so small. Planets orbit closer to Earth, so they appear much larger than stars do. Jupiter is 50,000 times closer than the nearest star, for instance. The small atmospheric shifts that make stars twinkle merely blur the fine details of a planets surface, leaving an otherwise stable image in the sky. To the naked eye, the image seems still. When Earths atmosphere gets extremely turbulent, however, nothing is immune from twinkling, not even planets. ---
**Author:** ![Podkayne](https://avatars.discourse-cdn.com/v4/letter/p/edb3f5/32.png) [@Podkayne](https://boards.straightdope.com/u/Podkayne)\ **Post date:** [August 10, 2003, 6:06pm UTC](https://boards.straightdope.com/t/what-would-the-martian-moons-look-like/194226/5 "2003-08-10T18:06:10Z")
Phobos is about 20 km. Its orbital radius is 9378 km. The radius of Mars is 3397 km, so that puts it 5981 km from the surface of Mars. That makes its angular size about 11 arcminutes, which is about a third the size of Earth’s Moon. If you’re planning a Phobos-viewing vacation, though, better book a hotel below 75 degrees latitude, or Phobos will never rise above the southern horizon because it’s so close to the planet. Deimos is about 12 km wide, and its orbital radius is 23,459 km, so it is 20,062 km above the surface. That means it’s only 2 arcminutes in size, so to the unaided eye it would be barely distinguishable from a star. They would both be bright, though. They’re small, but fairly close to the observer. From Earth, even, they’re 10 or 11th magnitude. I’m wussing out on the magnitude calculation at the moment, though, so I’ll post this much while I noodle around with that. ---
**Author:** ![yabob](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/yabob/32/2821_2.png) [@yabob](https://boards.straightdope.com/u/yabob)\ **Post date:** [August 10, 2003, 6:12pm UTC](https://boards.straightdope.com/t/what-would-the-martian-moons-look-like/194226/6 "2003-08-10T18:12:09Z")
> [@](#): > > That’s not a function of them being planets, but rather a function of them appearing slightly larger in the sky than stars. Also, planets can twinkle under certain atmospheric conditions. I know that. That was my point - that the apparent diameter of Deimos would probably be enough to prevent twinkling with Earth’s atmosphere under normal conditions. I should have said planets don’t USUALLY twinkle. ---
**Author:** ![Podkayne](https://avatars.discourse-cdn.com/v4/letter/p/edb3f5/32.png) [@Podkayne](https://boards.straightdope.com/u/Podkayne)\ **Post date:** [August 10, 2003, 6:56pm UTC](https://boards.straightdope.com/t/what-would-the-martian-moons-look-like/194226/7 "2003-08-10T18:56:24Z")
Whoops–that’s 69 degrees latitude. And if you’re above 75 degrees _south_ latitude, it won’t rise above the _northern_ horizon. Me an my north-hemispherocentric thinking . . . Australians, Africans, South Americans, and others, feel free to mock me. 🙂 Okay, I calculate the apparent magnitude of Diemos from the surface as -7 and of Phobos as -10.6, both of them in the full phase. By contrast, the magnitude of a crescent Moon is -9. (Remember that the more negative the magnitude, the brighter and object is.)