I imagine a situation must happen sometimes where a telescope watching a very dark object may catch a bright flash of light or a reflection off of a satellite. If that's even a concern at all (maybe all such telescopes are already designed to exclude that possibility), what countermeasures against blinding someone's eyes or frying the digital photo sensors are there?

  • $\begingroup$ I doubt if satellite flares are any danger, either to telescopes or observers. The simplest answer is: don't point your telescope at the sun. $\endgroup$ – Mick Nov 26 '17 at 9:14
  • $\begingroup$ @Mick have you ever considered a sun glare from a passing satellite could be pretty bright? The simplest answer is not what I'm looking for here. $\endgroup$ – user1306322 Nov 26 '17 at 11:19
  • $\begingroup$ Have you actually looked at satellites, say thru binoculars? They only appear bright to a dark-adapted eye. $\endgroup$ – Carl Witthoft Nov 27 '17 at 16:25
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    $\begingroup$ It's literally impossible. There just isn't enough energy in such a reflection to do any damage to the sensor. Consider this example: you could point the scope at the full Moon, leave the shutter open, and the sensor will be fine. $\endgroup$ – Florin Andrei Nov 27 '17 at 21:26
  • $\begingroup$ I'm going to support Florin's answer on this. I have a reflecting telescope with a 200mm primary mirror. I can look at the full moon through it - it's not pleasant because it's far too bright and it's uncomfortable, but my cameras are fine. $\endgroup$ – MartinV Nov 28 '17 at 17:41

Random bright objects can occasionally appear in astronomical images. Examples include asteroids and satellites. However, these objects are not moving at the sidereal rate across the sky, and thus unless the telescope is set to track them, they leave a trail across the image.

This is unlikely to cause damage and CCD detectors are fairly robust to saturation of exposures in any case. However, it may ruin the image.

  • $\begingroup$ I'm hard pressed to see how even a glint from a satellite could reach CCD damage levels -- see the rules about etendue, e.g. physics.stackexchange.com/questions/234996 . Blooming, I agree, could happen. $\endgroup$ – Carl Witthoft Nov 27 '17 at 16:24
  • $\begingroup$ @CarlWitthoft You may be right. It may be impossible to damage a CCD in this way. $\endgroup$ – ProfRob Nov 27 '17 at 17:25

Unless you happen to watch a nuclear explosion or a gamma ray burst or anything like that (very, very unlikely), no ordinary object in the night sky reflects or emits enough light to damage your eyes or fry your chip. Partly because they are very far away.

The only thing in the sky that can and will do that is the sun. So if you are watching at night, you are perfectly safe. So is your camera.

What can happen is that watching the moon or Jupiter can wreck your eye's ability to view faint or dim objects. Eyes need up to 30 minutes (give or take) to adapt to solid darkness. Brighter objects will partly or completely reset that ability so you have to wait a while until your eyes are truly sensitive again.

Imagine this: The moon is the brightest thing in the night sky. You can watch it all night long. If you use a bigger telescope, a gray filter might be nice, but it's not bright enough to heat your eyeballs. Numbers on the internet range between 1/400000 and 1/1000000 as bright as the sun.


While I agree with all the other answers here that no satellite flare has any chance of being bright enough to damage eyes or instruments there are concerns about them wrecking observations. Wikipedia reports that Iridium flares can reach magnitude -8 or brighter (Venus can be -4, the full moon is -12) and that could certainly be bright enough that scattered light from it would drown out some dim star or galaxy that you were trying to observe. If the flare can be predicted then you can always shut off the detectors for a short period, but some flares come from out of control satellites that are tumbling unpredictably.


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