[lmilcin]

There is a lot of occasions for observations if you are into it.

This photo is not a happy accident, though. It took careful preparation.

Let's see... it looks that at a distance of 400km we can see features of size roughly 1m (or even better). This points to resolution of 0.01 arcsecond which is fenomenal for an amateur setup.

[gliptic]

That's not quite right. 1 meter at 400 km distance is ~0.51 arcseconds, which is on the edge of doable with good seeing. 0.01 arcseconds would never be possible within the atmosphere.

[jcims]

The most depressing statistic here (for me anyway) is that to directly image the nearest exoplanet at 1km per pixel we're going to need a telescope with ~.000000005 arcseconds of resolution.

Someone check my math but that would be like imaging the ISS at the nanometer scale from the surface of the earth.

[krisoft]

I heard about this fascinating idea of using the gravitational lensing of our own sun to image the surface of exoplanets: https://www.youtube.com/watch?v=NQFqDKRAROI

It wouldn't look like any telescope you might have ever seen. Once we have a candidate exoplanet we want to take a picture of we would launch a flock of free-flying solar-sail propelled satellites in such an orbit that they get yeeted away from the sun on a trajectory opposite of the target exoplanet. They would travel to the "focal plane" of the sun's gravitational lens where the exoplanet's light is smeared to a ring around the sun which they collaboratively capture. Probably one such a pass wouldn't be enough, so we would need to send such flocks multiple times, like waves following on each other.

What I love about the plan is that it is both super scifi, yet we already have all the components to make it happen if we want to.

[rocqua]

Now compute what kind of virtual aperture size it takes to get this resolution without being diffraction limited.

Edit: I did it, about 25000km (for light with a wavelength of 500nm), or twice the radius of the earth. That actually suggests it could be doable with a constellation of telescopes in high orbit.

[nullc]

Or a gigantic obstruction: https://www.nasa.gov/content/the-aragoscope-ultra-high-resol...

Sadly the occulder has to be smooth at sub wavelength scales, or solar system bodies could be used.

[rocqua]

I couldn't find a quick summary to this question. But what size aragascope do you need to achieve the equivalent of an x meter aperture?

My gut says probably the same size, but the claims suggest the aragascope can actually be smaller. My gut can also imagine it depends on the distance between the aragascope and the telescope.

[nullc]

> the claims suggest the aragascope can actually be smaller.

This may be because of the shape of the PSF is different from the normal airy disk one.

Here is a random google result showing the spot of arago, https://www.lighttrans.com/use-cases/application/observation... -- which looks to me like it would have poor contrast but good resolution. Though I'm out of my depth so it could be nonsense. :P

Edit: Ah, yeah the graph at figure 9 in the report linked on the linked page shows something like that.

[gliptic]

The synopsis on the site suggests the same size as the disk. But I guess it doesn't say it scales the same as with mirror size.

> can be used to achieve the diffraction limit based on the size of the low cost disk, rather than the high cost telescope mirror

[lmilcin]

Believe or not, that project is already underway and will use our Sun as a gravitational lens.

https://en.wikipedia.org/wiki/Solar_gravitational_lens

I predict in couple decades we will learn to build swarms of drone craft that we will send to the right location and they will be able to image nearby planets (one per swarm...) with at least ~10-40km per pixel if not better.

[spaetzleesser]

“Underway “ is a little strong. Putting something at 500 AU is still not really feasible within a reasonable timeframe.

But I think there are exciting things to come up in the next decades for sure.

[spaetzleesser]

1km would be fantastic but I think 1000km would already give us a ton of information.

[elboru]

A few months ago the ISS passed through my city during sunset, while me and my family were hanging out outside. It was an amazing experience. I saw it first, it was reflecting the sun so it looked like a shooting star but it was too slow for a shooting star and too fast for a plane. It was too bright for it to be satellite? So I googled ISS position and it matched! We were able too see it for a while.