Viewing distant celestial objects

[happyhacker]

TL;DR Summary

Observing fine detail on exoplanets.

Is it possible given theoretical instruments to see fine detail of an exoplanets surface? E.g. could someone with normal human sight some 100 LY away from Earth be able to observe the surface of Earth and all it's detail (but of course that time ago).

I'm thinking that the light (in the visible spectrum) would have diverged too much and if that is the case at what distance would a good resolution be available?

 

[russ_watters]

Is it possible given theoretical instruments to see fine detail of an exoplanets surface? E.g. could someone with normal human sight some 100 LY away from Earth be able to observe the surface of Earth and all it's detail (but of course that time ago).

I'm thinking that the light (in the visible spectrum) would have diverged too much and if that is the case at what distance would a good resolution be available?

No, but how far away depends on what you mean by "fine detail".

The problem isn't the light diverging, the problem is angular resolution.

 

[Vanadium 50]

the problem is angular resolution

A problem is angular resolution. We can always find more problems.

Another is light collection. If you want your picture to have ten million pixels, and the same received per light per pixel as a million pixel image, you need ten times as much light.

 

[hilbert2]

There exists this theoretical gravitational lensing plan by NASA:

https://exoplanets.nasa.gov/news/1461/want-to-see-the-surface-of-another-earth-use-our-sun/

That could give a good enough resolution image of exoplanets to see the shapes of continents (if there are liquid and solid regions on its surface) on it. Another approach for doing this would be to construct a huge space telescope array that would probably be the most expensive project ever done by anyone.

It seems that most physicists don't know that this idea is not completely impossible. It certainly sounds like that when you first hear about it.

 

[Keith_McClary]

If you want to resolve objects as small as 1 km, you need an angular resolution of $10^{-15}$. You need a telescope 670,000 km in diameter.
https://www.omnicalculator.com/physics/angular-resolution

 

[happyhacker]

...
It seems that most physicists don't know that this idea is not completely impossible. It certainly sounds like that when you first hear about it.

Practically so one might think. i would have thought the light from the Sun would blot out the desired image or am I not thinking right here?

 

[sophiecentaur]

You need a telescope 670,000 km in diameter.

That figure assumes that you're using a telescope with a circular aperture (a mirror or a lens). `````````````````````````````` Most calculations assume this because you want as much light as possible and as good resolution as possible. However, there are a number of composite telescopes with several smaller reflectors, spread over a large area (This sort of idea. but much much bigger). The wide baseline improves resolution but admits much less of the light flux. That can, to some extent, be compensated for by having much longer exposure time.

A baseline of nearly 1Mkm would involve a vast array up in space and those particular numbers would, I think, not be achievable. But never say never. This technique is easier to achieve with radio telescopes than with optical telescopes. That could conflict with the "viewing" requirement in the OP but astronomical information is gathered in any way that works.

 

[davenn]

Summary:: Observing fine detail on exoplanets.

Is it possible given theoretical instruments to see fine detail of an exoplanets surface?

We cannot resolve fine detail on other stars ( which are much bigger) let alone a planet around that star

 

[sophiecentaur]

We cannot resolve fine detail on other stars ( which are much bigger) let alone a planet around that star

Perhaps the most likely feature that we would see in a distant solar system (apart from the planets (as dots) would be a massive telescope array, of the kind we might build.
The recent success on spotting exoplanets and the possible analysis of their atmospheres has tempted people into expecting even bigger leaps in our observational abilities. A few extra decimal places are not to be taken lightly.

 

[MikeeMiracle]

To scale this down somewhat, as I understand it Hubble is not even capable of seeing the moon lander. Each pixel would be something like a 3m by 3m square which is bigger than the lander.

 

[glappkaeft]

To scale this down somewhat, as I understand it Hubble is not even capable of seeing the moon lander. Each pixel would be something like a 3m by 3m square which is bigger than the lander.

Significantly more than 3x3 m. I have often seen 200x200 m but this ESA Hubble page says about 40x40 m best case after post processing etc.

 

[Keith_McClary]

theoretical gravitational lensing plan by NASA

FINAL REPORT PHASE II 85 pages, March 2020

 

[hilbert2]

FINAL REPORT PHASE II 85 pages, March 2020

Good to see its planning is that well in progress.

 

[stefan r]

No, we'd have even battier conspiracy theories about the Hubble hoax.

The Hubble Telescope Hoax | Aplanetruth.info. Link is clearly not peer reviewed link. Scroll down to comments section for entertainment purposes though.

If you want to resolve objects as small as 1 km, you need an angular resolution of 10^-15. You need a telescope 670,000 km in diameter.
https://www.omnicalculator.com/physics/angular-resolution

Convert a family of Hilda group asteroids into dishes and make an interferometer array. That gets 1 meter resolution. Easy peazy.

The sednoid arrays will get resolution down to cm scale. That isn't quite good enough to study most exo-plants because there isn't enough light emitted. The images have to be long exposure times. Exo-animals would move around too much. We might see effects like dung droppings, nests, tracks, or grazing patterns. Without radical life extension I am not expecting to see data collected by the Sedna colony.

 

[Nugatory]

An entertaining but thoroughly off-topic digression has been moved to https://www.physicsforums.com/threads/moon-landing-hoax-redux.997462/

 

[mfb]

Convert a family of Hilda group asteroids into dishes and make an interferometer array. That gets 1 meter resolution. Easy peazy.

An Earth-like planet will radiate ~1 kW/m², which means a 1 m² area will radiate 1 kW. At ~2eV/photon and a distance of 100 light years this leads to a flux of 10^-15/(m²s). If you want to take a picture with an exposure time of one second (you'll need to follow the planet's surface very precisely for that) and get 10 photons per square meter then you need an area of 10¹⁶ m². That corresponds to a square with a side length of 100,000 km, spread out over a larger area for the angular resolution. You could try building a million 100 km telescopes, or a trillion 3 km telescopes. That's ignoring the challenge to keep out any sort of stray light, keeping all these telescopes aligned with nanometer precision, combining their light and so on.

 

[SpaceJacob]

Last night, when I went out to observe starts, I got the idea to have my own satellite to observe stars, exoplanets, and our Earth. I know that even university students build satellites and launch them into space. Why can't we do the same? Having a telescope is amazing, but having its own satellite in orbit is breathtaking. Well, if one day I decided to create my own satellite, I'll certainly equip it with a Gecko imager. I know that Dragonfly Aerospace builds sats and imagers for civil customers, so it let's everyone cooperate with it. Isn't it an amazing idea?

 

[Vanadium 50]

Do you think a camera on a CubeSat will do better than the Hubble? Or even a medium-large terrestrial telescope?

Also, how do you plan to keep it pointed at its target?

 

[russ_watters]

Last night, when I went out to observe starts, I got the idea to have my own satellite to observe stars, exoplanets, and our Earth. I know that even university students build satellites and launch them into space. Why can't we do the same? Having a telescope is amazing, but having its own satellite in orbit is breathtaking. Well, if one day I decided to create my own satellite, I'll certainly equip it with a Gecko imager. I know that Dragonfly Aerospace builds sats and imagers for civil customers, so it let's everyone cooperate with it. Isn't it an amazing idea?

Well, you first have to decide exactly what you want and what your constraints are. Once you've figured that out, then you can decide what type of system will meet your needs. Putting a telescope in space -- and no, that Gecko Imager doesn't really qualify as a "telescope" -- is expensive, and there are almost certainly much cheaper terrestrial options. A cheap backyard telescope would be vastly superior to the Gecko Imager.

 

[Vanadium 50]

I just looked it up. Google tells me "A typical CubeSat launch cost is estimated at $40,000. T"

$40,000 buys you a lot of ground-based telescope. A lot of telescope.

 

[russ_watters]

I just looked it up. Google tells me "A typical CubeSat launch cost is estimated at $40,000. T"

$40,000 buys you a lot of ground-based telescope. A lot of telescope.

I think it's worth noting also that once you're willing to go with remote control, that opens up a ton of otherwise expensive options. Instead of buying a $40,000 system, you can rent one - in a prime location - for $100 a night.

 

[SpaceJacob]

I just looked it up. Google tells me "A typical CubeSat launch cost is estimated at $40,000. T"

$40,000 buys you a lot of ground-based telescope. A lot of telescope.

I know it's expensive, but why not aim for something better? We all need to have a source of motivation to move forward. Finally, we all dream about something: you want to buy a telescope, I want to launch CubeSat, and it's okay.

 

[russ_watters]

I know it's expensive, but why not aim for something better? We all need to have a source of motivation to move forward. Finally, we all dream about something: you want to buy a telescope, I want to launch CubeSat, and it's okay.

Well...it's ok as long as you recognize that your stated goals (thin as they are) contradict each other. You want "better" and you want a CubeSat. You need to pick one, because a small camera in a CubeSat isn't better than even a modest ground-based telescope.