If we had a powerful enough telescope, could we see footprints on the moon?

Question

If we had a powerful enough telescope, could we see footprints on the moon?

Answer 1

The ability of a telescope to distinguish small features is called the "resolution".



For visible light, the smallest resolvable angle (call it A in the equation) is calculated using "Dawes Limit"

http://en.wikipedia.org/wiki/Dawes%27_limit



A = 116/D

where A is the smallest resolvable angle in arc-seconds (there are 3600" in one degree) and D is the diameter of the main mirror (or lens) in mm (also called the aperture).



Then, there are problems with the Earth's atmosphere. Bur, for now, let's ignore that one.



The largest telescope in use is in South Africa and has an aperture of 11 metres (11,000 mm)



Its smallest resolvable angle is



A = 116 / 11,000 = 0.01"

(I am rounding off figures all over, but you will still get a good idea of sizes).



The Moon's average distance from us (centre to centre) is 384,400 km.



The Moon's orbit is an ellipse so that it is closer than that to us half the time, plus we are not at the centre of Earth. Still, the distance to the Moon's surface is always greater than 300,000 km



The smallest resolvable angle is 0.01" and, at a distance of 300,000 km, this corresponds to a size of

300,000 * Sin(0.01") = 0.015 km = 15 m = 50 feet.



Unless the footprints are bigger than 50 feet across, we can't see them, even in the world's largest telescope.



Since the relation is inverse linear (to see something half as big, we need a telescope twice as large), then to see a 1 foot footprint we need a telescope 50 times bigger.



A 550 metre telescope.



The present forecast is for a 100 m telescope within about 25 years. So a 550 m telescope should exist by the year 2100.



All the above is in theory only, since the Earth's atmosphere ruins everything.



Even with adaptive optics, the best we can ever hope for (even with the 11 metre telescope) is a resolution of about 0.1", putting the size limit (for objects on the Moon) at 500 feet across.



We can't even see the base of the lunar landing modules (30 feet across, if you include the extended landing pads).



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The only way to "see" the landing bases was to send a probe with a high-res camera.

http://www.nasa.gov/mission_pages/LRO/multimedia/lroimages/apollosites.html

scroll down to Apollo 14 site pictures (taken in 2009) from an orbiting mapper.

Actually, we still don't see individual footprints, but we can make out the footpath between the lunar lander and the instrument package.

Answer 2

No telescope has sufficient resolution to see anything that small, nor would any Earth-based telescope be able to view it, as the distortion from the Earth's atmosphere would be enough to obliterate the view. However, NASA's Lunar Reconnaissance Orbiter recently took pictures of many of the landing sites (similar to how satellite photography is done here of Earth), which are available here: http://www.nasa.gov/mission_pages/LRO/multimedia/lroimages/apollosites.html

Answer 3

No. Recent pictures by a lunar orbiting satellite with very low orbit altitude and very high resolution cameras can resolve the LEM descent stage and some of the instrument packages left from Apollo 11, and there are a couple dark streaks which are likely the tracks of the astronauts' footprints.



There is not a strong enough telescope to resolve these items from the Earth's surface nor even from Earth orbit, like the Hubble Space Telescope. Do a search for "telescope resolution" and you'll find several articles explaining how this is so.



Think about this -- the whole Moon is about 2000 miles in diameter and 280,000 miles away, and it is about 1/2 degree (30 minutes of arc) across. Now, how big is a footprint? Way smaller... maybe the equivalent of 1 foot square (it's likely smaller unless you've got really big feet!)

1/5280 x 1/2000 = 1/10,560,000 so the angular size would be 3/1056000 or 3 millionths of a minute of arc. 0.000003 minutes is such a small angle that no telescope existing or planned can resolve it.

Answer 4

Telescopes are limited by the laws of physics. The best resolution of the largest telescopes can show only objects as small as a few metres across. The lunar landing sites _have_ been imaged recently by the Lunar Reconnaissance Orbiter in low orbit over the Moon.

Answer 5

Your EYES are powerful enough to see things millions of miles away! You can see the Andromeda Galaxy with the naked eye, and that is over 2 million light years away. You can see the Moon, and it is 250,000 miles away. Can you see an ant from 2 miles though? It is not about distance alone, it is about distance AND SIZE of the objects. At 250,000 miles away, Hubble cannot see anything smaller than a football field. Those galaxies it takes pretty pictures of appear much larger than anything left on the moon. We can't see them because they are too faint, not because they are too small. The smallest object that can be resolved by any telescope is determined by the size of the telescope itself. In order to see the landers on the Moon from here you would need a telescope on the order of a few hundred metres across. To see the landers clearly and identifiably (rather than a few pixels in an image) you would need a telescope several kilometres across. It is clearly not practical to build such a thing.

Answer 6

looking at the moon is ALMOST like looking at the sun.... the surface of the moon, its dust, is a VERY light white color, ALMOST as reflective as silver or chrome..... it is INTENSELY bright..... can YOU stare at the sun and see the flares and solar prominences which are MILLIONS of miles long? Can you stare into the headlights of a car and describe the shape of the filament?

Answer 7

The best answer to that is maybe. The managing directors of the Paranal and Keck observatories (who seem to have a bit of a rivalry going) have both claimed that using all of the telescopes at their respective installations as interferometers are supposed to be equivalent to telescopes far more than a hundred meters wide. They both claim that supposedly they will be able to resolve some of the Apollo footprints.



But for some strange reason, neither observatory has produced photos of said footprints. So their claims remain unproven.