Space Warps Talk

Green Spot

  • Trenton1979 by Trenton1979

    What is the green spot in


  • Jerry_Fraley by Jerry_Fraley

    Link only loads a blank page.


  • surhudm by surhudm scientist

    There is an extra space in the link.

    Here is the right one:

    The green spot seems to be an artefact to me too.


  • Tom_Collett by Tom_Collett scientist

    It's very green. So green that I suspect it only appears in the green image. The color images on the website are actually a composite of several images taken at different wavelengths*. It's like looking at the world through a red/green/blue plastic sheet and then reconstructing the full color image (It's similar to how the cones in your eyes work, but your brain does all the processing).

    Because it's so green, it's likely to be absent in the 'red' and 'blue' images. It could be a transient object that was only there when the green image was taken (they aren't simultaneous), or it could be a glitch that only affected the 'green' image.

    *basically different colors of light


  • Budgieye by Budgieye moderator

    It may be from a moving satellite. I must find out if satellites are removed from these images. They leave pure red,green,and blue blobs.
    Possibly a "green pea", a small galaxy that has lots of ionized oxygen.


  • ElisabethB by ElisabethB moderator

    Found a satellite trail 😄


  • drphilmarshall by drphilmarshall scientist, admin

    Nice, @elisabethb! 😃 Yeah, I think it's an asteroid or a satellite (not moving as fast as Els' though). The exposure time is about 30 mins, what does that mean for the height and speed of the object causing the spot?


  • Budgieye by Budgieye moderator

    green spot

    Exam time!

    It is a 3 colour image, with each image taken at a different time. The object appears in only one colour, green, and is a perfect circular disc. Possibilities are:

    The object was transient, lasting only a few seconds or minutes during the green exposure. Perfect incoming meteor, possible but unlikely. Variable star. A distant satellite (further away than geo-stationary) that was illuminated by the Sun during the green exposure, but was in the Earth's shadow during the other images.

    The object is an asteroid, though slow-moving and far away. Trans-Neptunian, or Trojan when Jupiter is stationary. But then what happened to the red and blue filter images. Removed by computer? Off the edge of the image? Red and blue taken on different nights to the green and the object moved?


  • Tom_Collett by Tom_Collett scientist in response to Budgieye's comment.

    A rotating asteroid with one surface bright and the other dark is also a possible explanation for it only showing up in the green.

    Given how close it is to the edge of the image, I think I prefer your option c) a slow moving asteroid that wasn't in frame for the red and blue image.