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Rosetta Photographs Its Own Shadow On Comet 67P/C-G

Posted by Soulskill on from the pretty-pictures dept.

mpicpp notes an image release from the European Space Agency showing the shadow of its Rosetta probe on the comet it's currently orbiting. The probe snapped the picture from a very low flyby — only six kilometers off the surface. The image has a resolution of 11cm/pixel. The shadow is fuzzy and somewhat larger than Rosetta itself, measuring approximately 20 x 50 metres. If the Sun were a point source, the shadow would be sharp and almost exactly the same size as Rosetta (approximately 2 x 32 m). However, even at 347 million km from 67P/C-G on 14 February, the Sun appeared as a disc about 0.2 degrees across (about 2.3 times smaller than on Earth), resulting in a fuzzy “penumbra” around the spacecraft’s shadow on the surface. In this scenario and with Rosetta 6 km above the surface, the penumbra effect adds roughly 20 metres to the spacecraft’s dimensions, and which is cast onto the tilted surface of the comet.

6 of 21 comments (clear)

  1. This is becoming a new trend? by ColdWetDog · · Score: 2

    Between Curiosity and Rosetta we seem to be in an age of Space Selfies.

    And they say that robots don't take after their creators....

    --
    Faster! Faster! Faster would be better!
    1. Re:This is becoming a new trend? by sysrammer · · Score: 2

      And they say that robots don't take after their creators....

      ...as long as they don't take off *after* their creators...

      --
      His ignorance covered the whole earth like a blanket, and there was hardly a hole in it anywhere. - Mark Twain
  2. There is science here by hamjudo · · Score: 4, Interesting
    This is more than just a selfie, the shadow cast by a known object adds depth, scale, and many other scientifically interesting details about the comet, and about the space craft itself.

    And for those who like science fiction... If any aliens are riding the Rosetta probe, they will have to duck while the picture is being taken.

    1. Re:There is science here by Pikoro · · Score: 2

      The sun is not a point source. This is the same reason you get 2 shadows during a solar eclipse. The umbra and penumbra. The probe is 6km above the surface and it's not big enough to completely block the sun at that range, hence the fuzzy shadow.

      --
      "Freedom in the USA is not the ability to do what you want. It is the ability to stop others from doing what THEY want"
    2. Re:There is science here by hey! · · Score: 2

      Hmmm. While your explanation is unquestionably true, I don't think you quite understood what the poster was asking. His question is, I think, about the sharp shadows behind ridges on the surface, not the shadow of the vehicle itself.

      I think his problem is an implicit assumption that if you drew a line from the center of the sun through the spacecraft, it would intersect the surface at a right angle. In that case you wouldn't expect cracks on the surface to display in such relief. However I believe that assumption is faulty, and that the rays of the sun intersect the surface at a considerable angle.

      This is not unlike seeing the shadow of a plane you are riding in on the surface of the Earth. Unless you are in the tropics, that shadow won't be directly beneath you. It will be off to one side. It will also be distorted as it is spread out across the non-perpendicular surface, but you won't necessarily notice that because of foreshortening.

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      Post may contain irony: discontinue use if experiencing mood swings, nausea or elevated blood pressure.
  3. Does that mean by mobby_6kl · · Score: 2

    Six more weeks of winter? Brrr.