Peek-a-movie!

By Phil Plait | December 19, 2008 10:22 am

I was just informed by Twitterer karabaic that the picture of Ganymede going behind Jupiter that I posted yesterday also comes with a very cool animation!

Much higher-resolution versions are available on the HST site.

The astronomers took a series of images of Ganymede as it orbited Jupiter and made an 18 second/540 frame animation of it. Very cool! That’s the advantage of observing bright objects: short exposure times means you can take lots of images, and in this case there is motion, too, so a movie becomes totally cool.

Totally awesome.

Credit: NASA, ESA, E. Karkoschka (University of Arizona), and G. Bacon (STScI)

CATEGORIZED UNDER: Astronomy, Cool stuff
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Comments (24)

Links to this Post

  1. Video of Jupiter eclipsing Ganymede « Meng Bomin | December 19, 2008
  2. Nice HST photos | Trains of the World | April 1, 2011
  3. Cool Astronomy images | SpaceWeb | December 22, 2011
  1. Boomer

    Awesome indeed! I watched the HD version, it’s spectacular.

  2. tripencrypt
  3. SeanDudeManDudeDude

    This rocks! So simplistic, and yet, so awesomely awesome.

  4. Very cool. I also learned from this that Jupiter’s day is quite short!

  5. On the HD version you can see slight chromatic abberration on Ganymede’s edges.

  6. Wow!!!!

    I am SOOO putting that movie up on my blog too!

  7. Algirdas

    Am I the only person who gets an impression that Ganymede orbits the polar region of Jupiter, and not, you know, around Jupiter? This must be some trick of perspective and image cropping. The center of mass of Jupiter + moons system must (at this scale) nearly coincide with the center of Jupiter itself, and that is what the moons are supposed to orbit around, are they not? In this movie Ganymede appears like a poodle spinning about elephant’s ankles.

  8. T_U_T

    I feel there is something wrong with that. The way the ganymede seem s to follow jupiter rotation, ganymede isn’t in jupiter synchronous orbit, is it ?
    Cloud formations seem to not to be moving at all, I have a strange feeling. It is for real Or it is a kind of elaborate prank ?
    Maybe I am just too sleepy and tired and there is nothing really wrong with hrat video

  9. Algirdas, most of the time Jupiter does not eclipse its moons, so why should Ganymede pass exactly behind the equator from this perspective?

    T_U_T, there does not seem to be anything wrong with the video to me. The timescale of the cloud movement is much longer than the rotation speed.

  10. Ben

    I really, really like this video.

    In response to T_U_T’s statement that this might be a hoax, this appears to be exactly what the Hubble Site claims it is: approx 2 hours of Jupiter/Ganymede viewing. Since Jupiter’s period of rotation is under 10 hours, we get to see it rotate about 75 degrees. If you track that “little” red storm that starts out on the left side, you can confirm this for yourself.

    As for cloud movement, I think you are just being thrown off by videos you have seen in the past, which are over much longer periods, where there is at most 1 exposure every rotation, so that a given storm is seen to stay in one place, and then the spinning of storms and relative motion of the bands becomes apparent.

    As for Ganymede’s orbit following Jupiter’s rotation, that is just not the case, since its orbital period is 172 hours, so we are privileged to watch just about 1% of it in this video. But this makes sense when since Ganymede’s average orbital radius is about 7.5 Jupiter diameters, so if this video started 40 hours earlier, we would need a MUCH wider view to see both bodies in the same frame.

    Finally, pertaining to Algirdas’ “poodle spinning about elephant’s ankles” comment, this confusion is also caused because we are only seeing 1% of Ganymede’s orbit, and because our view from Earth did not provide an edge-on view of this orbit. The orbit projected to our viewing angle of course ends up being an ellipse (same as all those spiral galaxies that look like ellipses from our vantage point), and if the video showed the moment 86 hours later when Ganymede passes in front of Jupiter, we would see it as a “bird flying around a giraffe’s neck”.

  11. Wow, that’s really cool!

  12. StevoR

    Excellent! :-)

    But which is bigger – Titan or Ganymede?

    I still get different peoples saying each is larger – & does counting the atmosphere for Titan’s size make any difference or not?

    Or is one larger in actual diameter but more massive?

  13. StevoR

    Biggest moon in our solar systenm – Ganymnede or Titan?

    Over the years & sources some say one some t’other. Is there any final answer?

  14. T_U_T

    Ben, agree, I guess, I was just too tired yesterday to really think about it.

  15. mitrax

    *my* impressions (i don’t pretend to be right, and i’m certainly no expert):

    this looks totally fake to me. I already got the feeling that something was wrong when looking at the picture in a previous post, but it’s even more obvious in the movie: what’s that specular higlight showing up on Ganymede ??? (it looks like a marble ball…)
    when you look at the HD version you can see Jupiter spinning (rather quickly) yet ganymede doesn’t change *AT ALL* except for the translation motion.
    To me this look like something made in 5 minutes with 3D studio or Maya, wouldn’t be surprised if it turns out to be an hoax.

  16. mitrax,

    I’m not sure what you mean by this highlight that looks fake. I thought it looked pretty much like every other photo of Ganymede I’ve seen.

    As for it not changing, let’s do some math. First, remember that Ganymede–just like Earth’s moon–is tidally locked to the planet it orbits. In other words, Ganymede always shows the same face to Jupiter. In other other words, its orbital period of 171.75 hours is also its rotational period. The video was compiled from pictures shot over a 2 hour period. Ganymede appears in about 14 seconds of that 18 second video (I was too lazy to get an exact frame count for the moon), meaning that we’re seeing Ganymede for (14/18)*2hours = 1.6 hours (roughly). Since Ganymede’s rotational period is about 172 hours, what you are seeing in the video, is about 0.9% of Ganymede’s rotation.

    Do you really think that you would be able to see a less than 1% rotation? (hint: In the high definition video, Ganymede’s diameter is only 50 pixels.)

  17. mitrax

    The Science Pundit,

    I must admit i wasn’t familiar with what Ganymede looked like before seeing the video, what i mistakenly saw as a specular highlight (as in, light reflected from a light source to the viewer on a shiny surface) is indeed a large whitish spot on the moon that i can now see on other pictures. DUH
    Thanks a lot for your explanation, it makes perfect sense, it’s just that, ‘intuitively’ speaking (for someone who really doesn’t know much about astronomy / astrophotography) the video felt fake… a good example of how one can fool himself when he doesn’t know much about something!

  18. Nemo

    I can only get the video to say “Playback of this video failed. Please try again later.” :-(

  19. Nemo

    Got it from the HST site.

  20. StevoR

    Sorry about the double post yesterday folks – afraid I was in a hurry & unsure if the first one had gone through .. :-(

    But can anyone answer my questions please :

    1) Which is the solar system’s largest moon – Ganymede or Titan?
    (Various sources keep saying one or the other but still not sure which.)

    2) Is the answer to (1) affected by whether or not you count Titan’s atmosphere?

    &

    3) Does density / mass make a difference here? Ie. is Ganymede larger but Titan more massive or vice-versa?

    Answers anybody? Please?

  21. Someone

    Here’s the output from the JPL’s Solar System Simulator for the same date and time:

    http://space.jpl.nasa.gov/cgi-bin/wspace?tbody=599&vbody=399&month=4&day=9&year=2007&hour=14&minute=00&rfov=120&fovmul=-1&bfov=50&porbs=1&brite=1

    That is Jupiter as seen from Earth on April 9th, 2007 at 14:00 UTC (I don’t know when the data was recorded by Hubble, but based on the simulator output, it must have been around that time.)

    For Algirdas, and other people wondering about the “poodle spinning about about the elephant’s ankles”, remember that the axis of both Earth and Jupiter are inclined with respect to the ecliptic. The JPL simulator output displays a line along Ganymede’s orbit, which makes the effect of the axial tilt quite clear.

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