Could a mirror/s be made to reflect one side of the Earth from the edge of the solar system and viewed with a optical or radio telescope that is in orbit? With night vision, along with radio and thermal measurements, could something like this be used like CCTV for the World?

Blurring from the atmosphere can be mitigated by having the telescope in orbit aimed at the distant mirror/s which is aimed at a targeting mirror in synchronous orbit which is aimed at the Earth. The mirror in orbit can be moved to see different points on Earth. The telescope and mirror orbiting the Earth would be accommodating the not so adjustable long distant mirror.

In the comments: What if the Hubble was aimed at the Earth so that you could see stuff on a table, but it would be blurry. The fact that you could see anything at all on a table is impressive. Therefore, could it see a gun firing at night, or the color of a car, or when and where a plane went missing, although it may be blurry?

I understand that radio telescopes do not work the same as optical telescopes, but could radio telescopes also see better in this arrangement?

An image of a Magnetic Sail



  • $\begingroup$ I believe that we would have trouble making a mirror big enough, and also alignment and stuff would be tricky. Feasibility is no, but someone with math skills may be able to tell you if its theoretically possibly. $\endgroup$ – Clay Deitas Sep 5 '18 at 3:53
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    $\begingroup$ Light tends to drift due to quantum weirdness, so if the distance is too great, it becomes very blurry. $\endgroup$ – forest Sep 5 '18 at 3:59
  • $\begingroup$ @forest what distance is that? $\endgroup$ – Muze Sep 5 '18 at 5:09
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    $\begingroup$ It'd be a lot cheaper to send up a camera & broadcast back what it captured. $\endgroup$ – GrandmasterB Sep 5 '18 at 6:17
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    $\begingroup$ Duplicate? Yes. Useful closure? No. Frankly, if the duplicate target was closed as unclear then by definition the duplicate referent is unclear or the closure was invalid. However, the observation is irrelevant, the question is too broad with too many open-ended questions. $\endgroup$ – JBH Sep 5 '18 at 17:04

Light spreads out as it travels, proportionate to the square of the distance traveled. This is called the "inverse square law". Think about shining a light on a wall - the further away you are, the larger the circle on the wall, and the less bright it is. Less photons per square inch are arriving at the final destination.

By the time you get out to the edge of the solar system, The light is so spread out that your mirror would have to be absolutely gargantuan - Half the size of the solar system. It would also have to be curved, to avoid the light spread out any further.

As other people have mentioned - focusing issues, dust, gases and other objects in the solar system, as well as quantum weirdness are all acting against you.

  • $\begingroup$ Yes, but at what distance would resolution be a problem. Would there be enough resolution to follow a car? You don't have to see the whole Earth at once. $\endgroup$ – Muze Sep 5 '18 at 19:52
  • $\begingroup$ I believe this answer is misinformed. You don't need to make a giant mirror to compensate for the light become dimmer as it spreads out (though it certainly helps). You can just have a longer exposure time to collect more light. What you do need a bigger mirror for is to improve the resolution, though this would depend on the final optical configuration I guess. $\endgroup$ – Snyder005 Sep 5 '18 at 19:55
  • $\begingroup$ Wouldn't a curved mirror of this size be dangerous in terms of concentrated energy? $\endgroup$ – Hawker65 Sep 7 '18 at 8:59
  • $\begingroup$ @Snyder005 Wouldn't a long exposure time prevent you from seeing moving objects and defeat the whole point of CCTVing Earth? $\endgroup$ – Hawker65 Sep 7 '18 at 9:02
  • $\begingroup$ Depends on how long an exposure time you need. Unless you had really sensitive, extremely low-noise sensors, you're probably not getting 60 fps. Could be 1 frame per hour or day potentially. Anyways to see anything moving you'd need supreme resolution. The point was that resolution was the reason you needed the big telescope, not just because the light was dim. $\endgroup$ – Snyder005 Sep 7 '18 at 17:39

While this wouldn't work with a mirror, there is a way it's theoretically (though not practically) possible: by using a black hole.

When light approaches a black hole, some of it ends up getting drawn in, while some of it has its trajectory bent hyperbolically and flies off elsewhere. In practice, this looks like a shining band of light outside the hole's event horizon.

With an infinitely-powerful telescope, you could find a black hole and zoom in on just the right point the edge to see light that left Earth aeons ago, got warped around the black hole, and came back toward Earth. In effect you'd have a camera pointed at the past.

(Look at Riccardo Antonelli's description for much more detail on this, plus pretty pictures, and a program to make your own!)

The real problem lies in making an infinitely-powerful telescope, as current ones aren't anywhere near powerful enough for this: we've never even seen a black hole directly yet (depending on your definition of "seen"), and there are some fundamental limitations that mean we can't just keep scaling up our current telescopes to make them stronger. But handwaving a super-powerful telescope is far from the strangest thing that's been done in science fiction.

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    $\begingroup$ Problem is, that light gets mixed up with light from other sources. You won't get any pictire out of it. $\endgroup$ – Renan Sep 5 '18 at 12:36
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    $\begingroup$ Downvoted because the same problems that would cause a mirror to be dismissed as impossible are still present when using a black hole to "return" the light to Earth. You are effectively replacing the mirror with a black hole and introducing even more problems. In fact it's extremely more plausible to use a giant mirror than to use a black hole, so I don't see why you dismissed the mirror as impossible. $\endgroup$ – Snyder005 Sep 5 '18 at 19:49
  • $\begingroup$ @Snyder005 Basically because with a black hole you don't need to worry about the angle: if you choose the right spot to look at, you can see light that's approaching the black hole from any direction whatsoever. Whereas with a mirror that far away, the slightest error in angle would make the light miss Earth entirely. (A retroreflector avoids that problem, but a retroreflector also doesn't get you a nice clear image like OP wants.) $\endgroup$ – Draconis Sep 5 '18 at 19:55
  • $\begingroup$ But it's easier to hand-wave the problem of mirror alignment than the problem of determining the light-path of photons from the black hole disk. By the same principal, light from all the nearby stars/galaxies will also be visible, and will be intermixed with light from Earth. The optical effects of the accretion disk would also make focusing, let alone resolving the Earth much more difficult than the mirror. $\endgroup$ – Snyder005 Sep 5 '18 at 20:03

No mirror (or telescope spacecraft) can view an Earthly event earlier than its launch date. The light from any event before the launch is forever beyond the reach of a spacecraft that cannot exceed the speed of light.

Alien civilizations orbiting distant stars may, in theory, be examining our distant past, and might be persuaded to share their archives with us. We should immediately begin building enormous telescopes and recording the activities of alien civilizations in order to have something to offer in exchange.

A few spacecraft have looked back at Earth and returned distant pictures. The historical value of such photos is limited because they are severely blurred, probably caused by so many people constantly moving around.

  • $\begingroup$ But we could still attempt to set up a telescope that would allow us to view imagery from here on in the future without needing video storage correct? $\endgroup$ – The Great Duck Sep 8 '18 at 2:35
  • $\begingroup$ Yes, of course. Also, two mirrors in space, reflecting each other, could store an enormous amount of data. $\endgroup$ – A. I. Breveleri Sep 8 '18 at 3:10

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