After reading this question and seeing an image of ISS shot from earth, a doubt came in mind that if shooting moon from earth with high details is possible, why is it difficult to shoot artificial satellites from earth?
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$\begingroup$ It might have something to do with exposure time. Satellites move over the night sky with a high speed, so you need to track them with your camera during exposure or use a very short exposure time. The moon is a (relatively) static target, so you can use a camera fixture and a much longer exposure time. $\endgroup$– PhilippCommented Mar 14, 2014 at 9:16
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3$\begingroup$ What about geosynchronous satellites? $\endgroup$– Manu ViswamCommented Mar 14, 2014 at 9:18
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$\begingroup$ The ISS is at a height of 420 km. The geosynchronous orbit is 42,164 km - a hundred times the distance. The moon orbit is at 384,399 km, ten times the distance of GEO. That means the best we can get for a GEO satellite is ten times the resolution we can get for the Moon surface. $\endgroup$– PhilippCommented Mar 14, 2014 at 9:25
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$\begingroup$ So it should be more easy to take picture of an object which is more closer right? $\endgroup$– Manu ViswamCommented Mar 14, 2014 at 9:27
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2$\begingroup$ The Moon is BIG satellites are small. There are no high detail photos of the moon see the photo of LRV here. $\endgroup$– James JenkinsCommented Mar 14, 2014 at 10:21
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3 Answers
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There are two parts to this question. One is around speed (or apparent angular velocity) and one is around size.
The Moon's apparent velocity is small, so it is easy to set up a telescope or camera to take a photograph at an appropriate exposure. Many satellites, and the ISS are much closer, so the apparent velocity from the observer's perspective is a problem - you need to track at speed.
The Moon is big. The fact that you can take a good picture of it doesn't mean you are taking a picture at high detail. In fact you are getting pictures of the moon at probably lower detail than pictures of closer satellites. But the size of the moon means this probably isn't an issue. Being able to resolve a rock 50m across on the moon is overkill for many purposes, but even 20m resolution when trying to photograph a satellite probably means you can't see it at all.
There is also an issue around brightness - satellites have limited periods of visibility as they move in and out of the Earth's shadow, and typically are not visible at all during the day (obvious exceptions include Iridium flashes - but you need to know where and when to look). The moon reflects a lot of light, which makes finding, focusing and tracking it very simple.
answered Mar 14, 2014 at 11:22
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3$\begingroup$ Geosync is a very long way away. Satellites are tiny. We can see ISS with the naked eye as it is very close. Geosync satellites are not visible to the naked eye as they are smaller than the ISS and a hundred times further away. Reflectivity is not the issue - brightness is what I mentioned. $\endgroup$– Rory Alsop ♦Commented Mar 14, 2014 at 11:33
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2$\begingroup$ I have updated to say that even 20m resolution won't help you with a satellite photo. $\endgroup$– Rory Alsop ♦Commented Mar 14, 2014 at 11:34
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2$\begingroup$ The apparent velocity of the moon is only small in photographic terms because it's bright - if you try to photograph earthshine or include it in an HDR photo you'll realise how quickly it can cross a significant fraction of its own width! $\endgroup$– Chris HCommented Mar 14, 2014 at 13:47
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1$\begingroup$ In astronomy there's a concept that the size of the sky is measured in degrees squared... the moon has a solid angle of 0.2 deg^2 and an apparent magnitude of -12.74; the sun has the same area but an app. mag. of −26.74; the IIS has an area of ~0.0001994 (if I did the math right) and an app. mag. of -5.9 ... satellites are around 4 ... app. mag. is a logarithmic scale. $\endgroup$– KaitharCommented Aug 11, 2015 at 21:15
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1$\begingroup$ @Kaithar In my experience the ISS is usually closer to -2 to -1, and large satellites are 3 to 4. I remember reading somewhere that geostationary satellites are 9 or dimmer. $\endgroup$ Commented Dec 3, 2015 at 2:38
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Really simplified answer: Anyone can see the moon. It's huge. You normally can't see an artificial satellite, it's tiny. When you can see it, it's a tiny point, like a distant star. Same goes for a camera / telescope.
What you call "High detail" of the moon is probably tens or hundreds of metres across per pixel on the moons surface. A satellite is just not that big.
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4$\begingroup$ If you really want to simplify your answer to the extreme (whatever for?), then you might consider replacing tens or hundreds of metres with kilometers. ;) $\endgroup$ Commented Mar 14, 2014 at 19:27
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Interestingly, astrophotographers T. Kerss & B. Owens photographed a satellite flying in front of the Moon last year! It was a "normal satellite" if there is such a thing, and not something huge like the ISS.
https://twitter.com/ROGAstronomers/status/720254837095575552
You can read more about it in answers to What actually happened here with a satellite, the ISS and the moon?
It was a large telescope and still the satellite is just a dot, and moving really, really fast!
However, from space, one satellite can photograph another and resolve detail on the satellite! See answers to:
if it is bright enough:
and there are telescopes monitoring expensive communications satellites in GEO all the time that can see the parts fly off of a satellite once it's been hit by debris!
Screen shot (see the original tweet for the "GIF"):
