The shadow of a moon goes passing by

By Phil Plait | December 15, 2010 2:00 pm

The Viking 1 space probe settled into orbit around Mars in 1976, dropping a surface lander in the process. The probe stayed in orbit to monitor the planet, returning thousands of pictures from millions of kilometers away.

Those pictures are sitting in an archive, and sometimes have hidden jewels in them. As Emily Lakdawalla reports, somehow the keen-eyed Daniel Macháček spotted an amazing thing: the shadow of the Martian moon Phobos passing over a dust storm:

Wow! This animation is sped up by a factor of 10, and you can see the tiny moon’s shadow slip across the face of the planet. He also has one sped up 40X, and there you can see the slow movement of the dust storm, too… though it’s only slow due to distance; I’m sure someone standing on the surface would laugh ruefully at describing the 100 km/hr gusts as "slow". If they could breathe, that is.

Anyway, Emily has more information on the animations. I think this is amazing work, and we’ll be seeing more things like this as the planetary (and astronomical) databases get plumbed by the public. A lot of folks out there are very talented at digging out treasures, and equally adept at creating beautiful imagery and animations, too.

Related posts:

Martian Swirly
More incredible Phobos imagery
Phobos, close-up of fear
Martian dunes under a microscope

CATEGORIZED UNDER: Astronomy, Cool stuff, Pretty pictures

Comments (21)

  1. Oli

    I don’t see any stars so it must be fake.

  2. Office Casual

    The shadow appears elongated to me. Is that because the surface it’s passing over isn’t smooth? Any ideas?

  3. @ 3:

    It appears elongated because it is elongated. For two reasons: 1) the moon itself is oblong, and more importantly, 2) the angle at which the sun was above the local horizon was fairly low, so the moon’s shadow is stretched out over a larger chunk of territory than if it had been high noon. Same effect as when your own shadow gets longer as the sun goes down.

  4. I would totally brave the Martian winds to see a Martian lunar transit. An Earthly planetary transit would be even better!

  5. JScarry

    “I’m sure someone standing on the surface would laugh ruefully at describing the 100 km/hr gusts as “slow”.”

    But since the air is so thin, would it even knock you over if you were standing there?

  6. Office Casual

    @ 4

    Thanks, that seems so obvious now.

  7. Michael Swanson

    Are you sure it wasn’t one of those giant Martian amoebas you posted a picture of a while back?

  8. QuietDesperation

    Took me two tries to see it. :(

  9. Keith Bowden

    You’re ahead of me, QD – I finally glimpsed it at the end of my third pass and watched a fourth time. (Of course, at that point I felt a little dumb, but it was hard to see. Of course, for some reason I was expecting it to be a larger shadow coming from the right of the screen. Dunno why.)

    I must be tired…

    By the way, Phil – nice T’Pau allusion. (And if it was a coinkydink, then I am tired…)

  10. Messier Tidy Upper

    Well spotted Daniel Macháček. Amazing. :-)

    Faint and subtle just a passing shadow – which I presume wasn’t animated like that when he first detected it but rtaher in a series of still shots right?

    Goes to show its well worth going back over the old data ands images from old missions & that there’s still things in them we’ve missed first time around. Wonder what else is there that hasn’t been spotted yet?

    Would be awesome seeing the transit from the Martian surface – but, yeah, you’d definitely want a good spacesuit and O2 supply.I wonder who will be the first human to see that in Real Life – and when and from which nation. How long yet will we have to wait for Humanity to land on Mars – in person rather than via robot surrogates.

    I’m sure someone standing on the surface would laugh ruefully at describing the 100 km/hr gusts as “slow”. If they could breathe, that is.

    As I understand it, the pressure in the martian atmosphere is exceedingly low and so even if the gusts are 100km there’s not much to them because the air is so thin and lacking in “weight.” I could be wrong though.

  11. Kaveh

    it took me at least 6 tries to see it!

  12. Dave Jerrard

    Am I the only one that got the T’Pau reference?

    He Who Likes It With His Heart And Soul.

  13. Gary Ansorge

    “the T’Pau reference?”

    Perhaps you’re experiencing periodelia. I see nothing but the Shadow of The Death Star,,,

    Great pic.

    Gary 7

  14. Pete Jackson

    @No.5 Speedlimit186k: Such transits of the Earth-Moon system across the Sun as seen from Mars, although very rare, would be very beautiful. Imagine the extremely rare event where an occultation of the Moon by the Earth, or vice-versa, happened at the same time, as during a solar or lunar eclipse!

  15. Keith Bowden

    Thanks Dave (#13)! I’m glad I wasn’t the only one!

  16. PFINQ238

    Thanks! It makes me feel very small; also old.

  17. Matt B.

    What’s amazing is that that’s all penumbra. Phobos’ umbra reaches only one half to three fourths of the way down to Mars’ surface (depending on angle). Its penumbra is about 2.7 times its size (assuming a distance of about 7500 km from Phobos to Mars’ surface in this case), making it at most about 37 km wide (not counting the fact that it’s hitting the ground at an angle). I believe that’s smaller than our moon’s umbra.

  18. Joseph

    Are there images from space of our moon’s shadow traversing the earth during a Total eclipse?

    Or rather are there any good videos? A quick Google search reveals a black & white video that doesn’t work and a number of created animations.

    I want NASA video footage in color!

  19. Messier Tidy Upper

    @ ^ Joseph : Try this one :

    via the STEREO spacecraft & this very blog. :-)

    I’m afraid it’s not the Earth but the Sun instead but it’s still pretty impressive.

    Then there’s this artwork by Don Dixon :

    But, yeah, I couldn’t find much on that specifically either despite a quick search of this blog, google images and Youtube.

  20. Benjamin Franz

    @Dave Jerrard (#13): I got the T’Pau reference immediately when I saw the headline. Great song, great CD.


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