Asteroid Zoo Talk

What is that?

  • patatas by patatas

    There is some dark item on the center of the image which is moving in a linear way. Any ideas on what is this?

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  • CTidwell3 by CTidwell3

    It's an artifact of the image taking process. Things like dust on the camera or telescope lens. The artifact is not actually moving linearly. It moves up between frames 1 and 2, down and right between 2 and 3, and back left between 3 and 4.

    Artifacts sometimes have the illusion of linear movement t if you view the frames out of order -- i.e. 4, 1, (ignore 2) then 3. But that would be like viewing frames in a movie out of order.

    Imagine you have a car traveling east on and east/west road that is going to reverse direction by pulling into a driveway and backing out. You take 4 snapshots of this happening. Image 1 is when the car is facing east just before it turns left into the driveway. Image 2 is the car facing north fully in the driveway. Image 3 is car backed out into the road a little right of the driveway facing west. Image 4 is it traveling back towards the west facing west.

    Now image looking at these images out of order. 4, 1, 2, then 3. Imagine that you are also focused on the road and don't notice the driveway. You might see that set and say "Hey, it looks like a car driving in reverse (frame 4) suddenly does a 180 (frame 1), can't be seen in the next image (frame 2), and then appears to do another 180 and be driving in reverse (frame 3). It looks like it is moving in a general straight line with it just missing in frame 2."

    This is what can happen with these images sets. The relative positions of artifacts in images 1, 3 and 4 are usually about in a straight line, and when you have the images set on playback, it can be easy to see 4, 1, (2), 3 as almost straight line movement, especially if you don't notice the artifact moving up. Once you know this, however, it can become a tool for identifying artifacts. See something in frames 1, 3 or 4? Look up from frame 1, up and left from frame 3 or up and right from frame 4 to see if something is there. If there is, its a good chance you have found an artifact. Similarly, if you see something in frame 2, look down from there in frame 1, down and right in frame 3 or down and left in frame 4.

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  • patatas by patatas in response to CTidwell3's comment.

    Thank you, very useful informations

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