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0ld_Wolf t1_jdxgp20 wrote

Something you had not factored in is the Earth's rotational speed.

I read once that the Hubble could potentially resolve something the size of a textbook on a desk...but the image would be blurred/smeared so badly by the Earth's rotational speed that it would not be recognizeable.

So basically, only large structures like continents, oceans, ice caps, and clouds would be recognizeable at any distance - no matter the potential power of a telescope.


collegefurtrader t1_jdxpdcc wrote

There’s a whole constellation of US spy satellites in orbit that are very similar to hubble, and they track the earth just fine. Exposure times are much shorter too.


0ld_Wolf t1_je0nh99 wrote

What Hubble is designed to do and what spy satellites are designed to do are completely different.

I am not saying that the technology to resolve a clear image on Earth does not exist - just that it is not included on space telescopes designed to look at distances measures in light years.


UmbralRaptor t1_jdxh24v wrote

1 arcsecond angular resolution implies a linear resolution of 1 au at a distance of 1 parsec. We're deep within small angle approximation land, so can easily show what 0.1" gets you at varying distances:

distance resolution comment
1 ly 0.03 au Barring clever lightcurve reconstruction, you would not be able to tell that the moon exists
10 ly 0.3 au I'm unsure that you could find Earth. (I mean, JWST's coronagraph doesn't have the contrast for this, but I'm also concerned about the inner working angle)
100 ly 3 au This would be beyond the capabilities of even proposed telescopes like the HabEx starshade

FWIW, HST has a comparable angular resolution to JWST, as do some spy satellites. (notably the ones that took the image that Trump leaked)


jd-sutton OP t1_jdxl2s2 wrote

Just a quick note - the JWST is 0.1 not 1.. Not sure if you used 0.1 in your calcs but typed 1 in the comment or your calcs are incorrect. Can you clarify? Thanks


UmbralRaptor t1_jdxlc9h wrote

The 1 is just a rule of thumb thing that comes out from how the parsec is (well, was) defined.

so 0.1 arcsec * 1/3.26 pc ~= 0.03 au


Head_Weakness8028 t1_jdxohht wrote

I definitely see where you’re going with this. Assuming we could fold space-time and position a telescope as you mentioned. Also assuming that this hypothetical telescope is far more powerful, and could extract actual details from the surface of the planet; Then yes, the telescope would “out-pace” the photons reflecting from the earth, and you could hypothetically see anything during earths history. Interesting thought experiment for sure. With our current understandings of the universe it seems the only time traveling we can do is into the future. By either traveling at velocities near the speed of light or parking close to an extreme gravity source you can slow your local resonant frequencies as compared to those on the Earth.


SpartanJack17 t1_jdz9nuz wrote

Hello u/jd-sutton, your submission "Hypothetical question" has been removed from r/space because:

  • Such questions should be asked in the "All space questions" thread stickied at the top of the sub.

Please read the rules in the sidebar and check r/space for duplicate submissions before posting. If you have any questions about this removal please message the r/space moderators. Thank you.


noncongruent t1_jdxowzx wrote

The problem is that in order to see past events, you need to get the telescope out there faster than the speed of light. A photon leaving the Earth travels at the speed of light, and since no known or suspected technology allows traveling faster than light, or for that matter even at the speed of light, it means that no matter how far away you put the telescope it'll always only be able to catch photons that left Earth after the telescope did.