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I can't continue down this rabbit hole so I'm asking for a handout. I remember reading about the limitations of light and contrast to resolve smaller details on

by sosuke 6y ago

I can't continue down this rabbit hole so I'm asking for a handout. I remember reading about the limitations of light and contrast to resolve smaller details on the moon or other solar systems like this. I've since lost the details and links to time. Is there any upper limit, physically, to this? Would it be possible on paper to design a system that could take pictures of the moon where you could see individual strands of hair on a human? I'm curious if we might at some point construct enormous arrays of telescopes spanning large (human perspective) sections of space that could give us a window into our galaxy.

hammock 6y ago
HDR for astrophotography
semi-extrinsic 6y ago
There are several physical limits to how small objects can be resolved. Here is a discussion thread with regards to the smallest lunar object visible - seems to be around 350 meter resolution for an earth bound telescope. https://www.cloudynights.com/topic/712653-what-is-the-smallest-lunar-object-visible-visual-clearly-with-an-amateur-telescope/ https://www.cloudynights.com/topic/712653-what-is-the-smalle...
- JoeSmithson 6y ago
  But could images from several telescopes be combined through a Kalman filter or something to resolve higher details? I am imagining some kind of internet enabled telescope that knows it's GPS location and orientation, and phones home it's imagery to a central server. If millions of people bought and used a product like that, is it theoretically possible to see the lunar rover?
  - semi-extrinsic 6y ago
    https://en.wikipedia.org/wiki/Astronomical_interferometer https://en.wikipedia.org/wiki/Astronomical_interferometer TL;DR: for optical wavelengths, with typical image sensors that only detect amplitude and not phase of the electromagnetic wave, you need to do some really hard work to ensure optical coherency. For radio telescopes, it's a lot easier since you measure both amplitude and phase. Another technique that's a lot easier to accomplish for amateurs is lucky imaging: https://en.wikipedia.org/wiki/Lucky_imaging https://en.wikipedia.org/wiki/Lucky_imaging
    - SiempreViernes 6y ago
      In this context, it's relevant to note that the VLT was built with interferometry in mind, and they are now getting it to work reliably. See for instance the page about the GRAVITY instrument: https://www.eso.org/public/teles-instr/paranal-observatory/vlt/vlt-instr/gravity/ https://www.eso.org/public/teles-instr/paranal-observatory/v...
dmead 6y ago
i'm not expert. i have a back yard observatory with a 12 inch and an 8 inch SCT telescopes. there is a limit to how far information can propagate. but with wider and wider scopes we can deal with the wave properties of light and how those waves get wider and wider as you go farther away. (see the inverse square law) so, we could probably see a human hair on the moon, but the mechanism to do so would be the size of a city like LA or something. the best way we have to deal with that is actually interferometry. you take measurements of the light wave emitted by a source at several points along it's wave front and infer what the source would look like closer up. it's very fuzzy but gives us pictures of some very large very far away structures in the universe. so, maybe if we had enough telescopes pointed at the moon, we could see fine structures like that? but my feeling is that a lot of that information on that scale is just lost from the perspective of each scope, so you really need to capture all of it at a weirdly large scale.
throwaway2048 6y ago
https://en.wikipedia.org/wiki/Diffraction-limited_system https://en.wikipedia.org/wiki/Diffraction-limited_system There is a fundamental relationship between wavelength of light and focus-ability/magnification. You could in principle build an increasingly larger lense to get around the problem, but eventually that hits practical limits.
- robin_reala 6y ago
  For varying definitions of pratical. For example, you can use a star as a gravitational lens.
- webmaven 6y ago
  Can't you create ever larger arrays of reasonably sized lenses? And "array" just means "two or more widely separated by a known distance", so opposite sides of (polar?) orbit should work.

by sosuke 6y ago

hammock 6y ago

HDR for astrophotography

semi-extrinsic 6y ago

There are several physical limits to how small objects can be resolved. Here is a discussion thread with regards to the smallest lunar object visible - seems to be around 350 meter resolution for an earth bound telescope. https://www.cloudynights.com/topic/712653-what-is-the-smallest-lunar-object-visible-visual-clearly-with-an-amateur-telescope/ https://www.cloudynights.com/topic/712653-what-is-the-smalle...

JoeSmithson 6y ago
But could images from several telescopes be combined through a Kalman filter or something to resolve higher details? I am imagining some kind of internet enabled telescope that knows it's GPS location and orientation, and phones home it's imagery to a central server. If millions of people bought and used a product like that, is it theoretically possible to see the lunar rover?
- semi-extrinsic 6y ago
  https://en.wikipedia.org/wiki/Astronomical_interferometer https://en.wikipedia.org/wiki/Astronomical_interferometer TL;DR: for optical wavelengths, with typical image sensors that only detect amplitude and not phase of the electromagnetic wave, you need to do some really hard work to ensure optical coherency. For radio telescopes, it's a lot easier since you measure both amplitude and phase. Another technique that's a lot easier to accomplish for amateurs is lucky imaging: https://en.wikipedia.org/wiki/Lucky_imaging https://en.wikipedia.org/wiki/Lucky_imaging
  - SiempreViernes 6y ago
    In this context, it's relevant to note that the VLT was built with interferometry in mind, and they are now getting it to work reliably. See for instance the page about the GRAVITY instrument: https://www.eso.org/public/teles-instr/paranal-observatory/vlt/vlt-instr/gravity/ https://www.eso.org/public/teles-instr/paranal-observatory/v...

dmead 6y ago

i'm not expert. i have a back yard observatory with a 12 inch and an 8 inch SCT telescopes. there is a limit to how far information can propagate. but with wider and wider scopes we can deal with the wave properties of light and how those waves get wider and wider as you go farther away. (see the inverse square law) so, we could probably see a human hair on the moon, but the mechanism to do so would be the size of a city like LA or something. the best way we have to deal with that is actually interferometry. you take measurements of the light wave emitted by a source at several points along it's wave front and infer what the source would look like closer up. it's very fuzzy but gives us pictures of some very large very far away structures in the universe. so, maybe if we had enough telescopes pointed at the moon, we could see fine structures like that? but my feeling is that a lot of that information on that scale is just lost from the perspective of each scope, so you really need to capture all of it at a weirdly large scale.

throwaway2048 6y ago

https://en.wikipedia.org/wiki/Diffraction-limited_system https://en.wikipedia.org/wiki/Diffraction-limited_system There is a fundamental relationship between wavelength of light and focus-ability/magnification. You could in principle build an increasingly larger lense to get around the problem, but eventually that hits practical limits.

robin_reala 6y ago
For varying definitions of pratical. For example, you can use a star as a gravitational lens.
webmaven 6y ago
Can't you create ever larger arrays of reasonably sized lenses? And "array" just means "two or more widely separated by a known distance", so opposite sides of (polar?) orbit should work.