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Asteroids zooming past Saturn?

  1. Dec 28, 2012 #1
    After waiting about 10 days for clear weather last night and this morning I spent several hours testing a new observational rig: a very heavy high power set of binoculars mounted on a heavy tripod with a geared turret. Conditions were good: clear, still and cold (-4 degrees C) but with some frozen moisture from the ocean reflecting the light of the full moon just above the Western horizon.

    I was just able to detect Titan, Saturn's moon and double checked with this Java Applet that where I saw it was it's actual position

    But as I was scanning to find Titan, I saw nearby what looked like 2 very faint points of light that I first thought were stars. After a minute I could detect movement in relation to Saturn so I then thought one was a satellite. But watching further, they both moved in tandem in relation to the planet as if Saturn were traversing the background field of stars at the approximate speed of the rotation of the Earth.

    The reasonable explanation must be that they are asteroids with a solar orbit that roughly matches the Earth's rotation when viewed from our position. But they were so close together (about 5 minutes of arc) that I would think there would be some gravitational locking.

    This occurred about 5:30 GMT. Comments?
    Last edited: Dec 28, 2012
  2. jcsd
  3. Dec 28, 2012 #2


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    If they were asteroids, it is very unlikely that they are not gravitationally bound to sun. This gives a maximal velocity of ~80km/s relative to earth (where values above 50km/s are quite unlikely). To get a (true) angular velocity of 2pi/(24 hours), this corresponds to a maximal distance of 1.1 million km. Quite close, and I would expect that those objects would appear in some sky survey.

    I don't know the quality of your binoculars and your point of view - geostationary satellites would give a natural explanation for the apparent motion of the objects.
    (distance to titan)/(radius of titan)=600 000, in the geostationary orbit this would correspond to a radius of ~60m. Taking the different distance to sun into account, an object with a diameter of ~6m and the same albedo would appear as bright as Titan. Satellites are smaller, but they can be more reflective. In addition, the objects you saw are fainter than Titan. Might be possible to see them.
  4. Dec 28, 2012 #3
    Interesting figures. I'd say the 2 objects were about 1 magnitude higher in brightness than Titan but not as bright as Jupiter's moons which looked very beautiful the previous night and moved also from minute to minute as Io and Ganymede were close together and near to Jupiter.

    It would seem odd that 2 geostationary satellites would be so close to one another. They could have been space debris of some kind possibly.

    The binos are the Skymaster 30-125x80 by the way. The turret is the Manfrotto 405. I think the less expensive Manfrotto 410 would work fine too but I was lucky enough to find a used 405 which should be more durable. So far I'm very excited with the viewing that is possible, but really hanker after something outrageous like 600x160 binos as opposed to a telescope. Stereoscopic vision makes a large difference IMO.
    Last edited: Dec 28, 2012
  5. Dec 29, 2012 #4


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    To have visibly moved relative to saturn in such a short period of time, they had to be much nearer earth than saturn.
  6. Dec 30, 2012 #5


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    Geosync satellites can look pretty close in the sky. I've got a GIF I made that shows three of them, all within about 5-10 arcsecs of each other moving past the Orion Nebula. Now if I could just find that GIF...
  7. Mar 4, 2013 #6
    I think it is possible that you may have seen the TanDEM-X satellites in orbit. They fly very close together, between 250-500 meters! There are quite a few, twin and other multiple configurations flying in space. If you ever see such a thing again, make note of the time and go to the Heavens-Above homepage and enter your latitude and longitude. It will tell you exactly what was in the sky at the time. Even better get a prediction print out and spend an evening hunting them down.
    Here is an image of some NASA "tandem satellites" the twin satelites of the (RBSP) mission
    launchedlast year.

    Attached Files:

    Last edited: Mar 4, 2013
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