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Software should be able to account for this. If photoshop can remove people from photos, why can't astronomy software remove satellites? Orbit is already pretty

Software should be able to account for this. If photoshop can remove people from photos, why can't astronomy software remove satellites? Orbit is already pretty cluttered and we can't remove much that gets stuck up there already.

krastanov 7y ago
Software can make a picture look pretty, but it has very limited use when you are fighting against the limits of information theory. You want an actual new measurement, not a guess of what a reasonable measurement would look like based on past measurements.
- heavenlyblue 7y ago
  But that measurement is literally a dot that you know would not be there at time T-1, then should be there at time T and then shouldn't be there at time T+1. Astronomers are lazy.
  - doubleunplussed 7y ago
    It's not a dot, in a long exposure photograph, it's a line. You don't delete it spatially, you'll want to subtract off the extra photon counts along that line so you can retain whatever was in that part of the image. Now, I think that's possible - find lines one diffraction-spot wide, fit to its brightness and subtract it off. They should be damned near straight lines of constant brightness given how fast satellites move, and the transverse profile should be exactly given by your telescope's point-spread-function, so you should be able to locate them and model them for subtraction very well. I think it can be done. Photon shot noise is sqrt(N) though, so even after the subtraction you're left with more noise along that line than elsewhere. So that's not ideal. But increased noise is less of a concern that "totally ruined data". Another caveat is that the lines have to not be so bright as to saturate your CCD, otherwise you truly have lost data that subtraction won't help with. Edit: it turns out astronomers take many shorter exposures [1] and simply reject the pixels that are too far away from the mean in any given exposure when combining them. This seems mostly better than what I was proposing, though it does mean increased readout noise since you read out multiple times and so for very sensitive measurements I would still expect astronomers might want to do true single long exposures. [1] https://www.skyandtelescope.com/astronomy-blogs/imaging-foundations-richard-wright/satellites-begone-how-to-remove-satellite-trails-from-your-astrophotography/ https://www.skyandtelescope.com/astronomy-blogs/imaging-foun...
    - jdashg 7y ago
      You can't just subtract a bright signal and hope to see the weak signal underneath it, or we'd just subtract daylight during the day.
      - doubleunplussed 7y ago
        Depends how bright, I do it every day in a different context and it can work pretty well. The brighter, the more of that noise I was getting at. Sunlight is very, very bright , but satellites less so. I'd need to know how bright to know if the resulting noise would swamp the signal. Perhaps the fact that astronomers aren't doing this is evidence that it does.
takk309 7y ago
This isn't just about astrophotography, this has to do with real science too. Remember, most science work is already on a tight budget and now they will have to waste some of that budget sorting through the added visual clutter.
- kerng 7y ago
  It's like with nature on earth, tech pollutes things. It's not really anything new.
  - pretendscholar 7y ago
    its literally a new additional problem which is why its being discussed
    - deleted 7y ago
      [deleted]
- La1n 7y ago
  Yes, and SpaceX seems to be actively downplaying that fact. >. “We want to make sure we do the right thing to make sure little kids can look through their telescope,” she said. “Astronomy is one of the few things that gets little kids excited about space.”
buboard 7y ago
since starlinks may change positions autonomously it's impossible to predict their positions. and they are so damn many
- dnautics 7y ago
  You don't need a position prediction to remove an anomaly.
  - cbanek 7y ago
    Actually, you kind of do, because how do you know it's an anomaly and not something you want to observe? Especially if it's just occluding things in its path, and you can't see it. It's really helpful to know where everything is.
    - dnautics 7y ago
      Optical signature.
- nradov 7y ago
  Starlink satellites are too small to do much orbital maneuvering. They only carry a small supply of krypton gas for their station keeping thrusters.
  - greglindahl 7y ago
    They have enough propellant to change their orbital height by quite a lot, more than the typical satellite (other than GTO-to-GEO thrusters.) OTOH you can just ask SpaceX or the Air Force where they have been in the past, SpaceX uses GPS and the Air Force radar is accurate enough for knowing where they were.
    - londons_explore 7y ago
      If the astronomer community requested it, I'm sure spacex would give them a real-time (or even a few minutes ahead of time) feed of satellite positions accurate to less than a pixel on these telescopes.

krastanov 7y ago

Software can make a picture look pretty, but it has very limited use when you are fighting against the limits of information theory. You want an actual new measurement, not a guess of what a reasonable measurement would look like based on past measurements.

heavenlyblue 7y ago
But that measurement is literally a dot that you know would not be there at time T-1, then should be there at time T and then shouldn't be there at time T+1. Astronomers are lazy.
- doubleunplussed 7y ago
  It's not a dot, in a long exposure photograph, it's a line. You don't delete it spatially, you'll want to subtract off the extra photon counts along that line so you can retain whatever was in that part of the image. Now, I think that's possible - find lines one diffraction-spot wide, fit to its brightness and subtract it off. They should be damned near straight lines of constant brightness given how fast satellites move, and the transverse profile should be exactly given by your telescope's point-spread-function, so you should be able to locate them and model them for subtraction very well. I think it can be done. Photon shot noise is sqrt(N) though, so even after the subtraction you're left with more noise along that line than elsewhere. So that's not ideal. But increased noise is less of a concern that "totally ruined data". Another caveat is that the lines have to not be so bright as to saturate your CCD, otherwise you truly have lost data that subtraction won't help with. Edit: it turns out astronomers take many shorter exposures [1] and simply reject the pixels that are too far away from the mean in any given exposure when combining them. This seems mostly better than what I was proposing, though it does mean increased readout noise since you read out multiple times and so for very sensitive measurements I would still expect astronomers might want to do true single long exposures. [1] https://www.skyandtelescope.com/astronomy-blogs/imaging-foundations-richard-wright/satellites-begone-how-to-remove-satellite-trails-from-your-astrophotography/ https://www.skyandtelescope.com/astronomy-blogs/imaging-foun...
  - jdashg 7y ago
    You can't just subtract a bright signal and hope to see the weak signal underneath it, or we'd just subtract daylight during the day.
    - doubleunplussed 7y ago
      Depends how bright, I do it every day in a different context and it can work pretty well. The brighter, the more of that noise I was getting at. Sunlight is very, very bright , but satellites less so. I'd need to know how bright to know if the resulting noise would swamp the signal. Perhaps the fact that astronomers aren't doing this is evidence that it does.

takk309 7y ago

This isn't just about astrophotography, this has to do with real science too. Remember, most science work is already on a tight budget and now they will have to waste some of that budget sorting through the added visual clutter.

kerng 7y ago
It's like with nature on earth, tech pollutes things. It's not really anything new.
- pretendscholar 7y ago
  its literally a new additional problem which is why its being discussed
  - deleted 7y ago
    [deleted]
La1n 7y ago
Yes, and SpaceX seems to be actively downplaying that fact. >. “We want to make sure we do the right thing to make sure little kids can look through their telescope,” she said. “Astronomy is one of the few things that gets little kids excited about space.”

buboard 7y ago

since starlinks may change positions autonomously it's impossible to predict their positions. and they are so damn many

dnautics 7y ago
You don't need a position prediction to remove an anomaly.
- cbanek 7y ago
  Actually, you kind of do, because how do you know it's an anomaly and not something you want to observe? Especially if it's just occluding things in its path, and you can't see it. It's really helpful to know where everything is.
  - dnautics 7y ago
    Optical signature.
nradov 7y ago
Starlink satellites are too small to do much orbital maneuvering. They only carry a small supply of krypton gas for their station keeping thrusters.
- greglindahl 7y ago
  They have enough propellant to change their orbital height by quite a lot, more than the typical satellite (other than GTO-to-GEO thrusters.) OTOH you can just ask SpaceX or the Air Force where they have been in the past, SpaceX uses GPS and the Air Force radar is accurate enough for knowing where they were.
  - londons_explore 7y ago
    If the astronomer community requested it, I'm sure spacex would give them a real-time (or even a few minutes ahead of time) feed of satellite positions accurate to less than a pixel on these telescopes.