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Comment by CWIZO | Hacker News Reader

I always wondered what kind of telescope one would need to look at the stuff we left on the moon (flag, cars, what was left of the rocket, ...). Anybody know or tried that? Is equipment like that even accessible to a regular joe like me?

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Simple rule of thumb:

The resolving power of a telescope is a function of aperture (diameter of primary lens or mirror). A telescope with an aperture of 100 mm (4") has a resolving power of 1 arcsec. Then 200 mm of aperture buy you 0.5 arcsec, and so on.

What is the minimum size of detail to distinguish those objects? Let's say 10 cm - kind of blurry, but intelligible.

What's the distance to them, from a telescope in low orbit? It's approximately the semi-major axis of the orbit of the Moon - 384,000 km.

arctan ( 10 cm / 384000 km ) = 2.6 * 10^-10 radian = 5.4 * 10^-5 arcsec

The aperture you need to get that kind of resolving power is:

100 mm / (5.4 * 10^-5) = 1800 m

You'd need a telescope with 1.8 km of aperture to see the Moon lander with 10 cm linear resolution. Scale down the aperture if you're content with less resolution, the function is linear.

Please note this is for a scope in vacuum, above the atmosphere. Air turbulence will reduce its resolving power dramatically, requiring some kind of adaptive optics to dynamically counteract the blur, which typically is not 100% efficient.

Not possible because of optical resolutions. If you web search that question you'll get more details.

https://www.google.com/search?q=can+I+use+a+telescope+to+see...

Here are some responses:

http://answers.yahoo.com/question/index?qid=20100906195045AA...

http://stupendous.rit.edu/richmond/answers/lunar_lander.html

http://curious.astro.cornell.edu/question.php?number=134/

http://blogs.discovermagazine.com/badastronomy/2008/08/12/mo...

I was sure you could use the Hubble at least. Shows how much I know about this stuff :) Thanks for the links, they are quite informative.

Actually, I remember reading somewhere that the Hubble was in fact pointed at the Lunar landing sites at one point, but that even its resolution was too low to produce any conclusive images of the landing sites.

We just need to get the NRO to let us borrow one of their satellites :)

Well, not with a direct telescope, but optical interferometry could achieve the milli-arcsecond resolution needed.

http://en.wikipedia.org/wiki/Astronomical_interferometer

I'm not sure if there exists a telescope that has the resolution, but it's within current technology.

And to point out that not only do you need an Aperture that you can't currently get, you need to air to stop moving so that you can look through it. The heat in the atmosphere causes the gas molecules to bounce around and they tend to refract light so you end up with foggy vision.

Its also why you can't get a clear image of the ISS (which is in low earth orbit) or even geostationary satellites. This is something governments have taken advantage of. Once you launch a satellite its hard to 'view' it without actually being in space.

This should answer your question: http://www.telescopes.com/telescopes/canyouseeobjectsleftbeh...

tldr: you would need a 200 meter telescope to see the flag, or a 75 meter 'scope to see the lunar rover. The largest earth bound 'scope is 10meters. The Hubble scope is 2.4m

Also goes in to the 'rippling flag' question that someone asked in a different comment below.

It's not the same, but several Apollo missions left behind retroreflectors, tri-corner reflectors like in car taillights, which can bounce back laser probes:

http://science.nasa.gov/science-news/science-at-nasa/2004/21...

They are used to get precise earth-moon distances.

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