It's just so far away.
Let's do a rough calculation
Moon has angular diameter about 0.5 degrees and in kms it's 3500 km
Hubble has a resolution of 36,000 pixels to a degree so for the moon that's 18,000 pixels to cover the diameter of the moon, at 3500 km. I'm choosing Hubble because it's roughly comparable to the very best of our ground telescopes equipped with adaptive optics.
So each pixel is about 200 meters at the distance of the Moon. This is its "diffraction limit" - a limitation from pure physics based on the diameter of the telescope and the wavelength of light you use. There is no point in them trying to use a higher magnification - though you could do it in principle just by using powerful enough lenses or mirrors - but the resulting images would be fuzzy.
The only way to get to a higher resolution is to use a larger telescope (or several smaller telescopes acting together to simulate the effect of a larger mirror).
See The Diffraction Limit of a Telescopes
That's also why radio telescopes are so large - because the wavelength is larger - they need to use far bigger telescopes to get the same resolution.
So even Hubble, turned towards the Moon has no chance of seeing any of the Apollo landers - they are just below its best resolution.
As for ground based telescopes - then they have the problem of the Earth's atmosphere - so - though they can have larger mirrors than Hubble - and you can use several of them working together to emulate an even larger mirror - and can do adaptive optics also which to some extent helps to "untwinkle" the night sky - still - they aren't quite good enough yet to be able to spot Apollo on the Moon.
Indeed - they are still "chasing" Hubble, I think Hubble is still the best - except possibly when imaging the brightest stars using adaptive optics. And the James Webb telescope - though larger than Hubble, is optimized for infra red observation - and still won't have better resolution - it wouldn't be able to spot them either. High-resolution imaging with large ground-based telescopes
So - I don't think we have any upcoming telescopes either, on Earth or in orbit - that have much of a chance of spotting them. (Do correct me in the comments if you know of any that are!).
It looks so striking, e.g. the deep field images
Hubble Team Unveils Most Colorful View of Universe Captured by Space Telescope
You can zoom in and in on the image, seems, if you can see distant galaxies billions of light years away in such detail - why can't we see Apollo on the Moon?
But - galaxies are pretty huge things, the Moon is tiny in comparison. And Apollo is even tinier compared to the Moon.
Even zoom right in, then Apollo on the same scale would be far smaller than a single pixel in this image.
It's at least an order of magnitude too small - just a little bit below the visual resolution of Hubble (not that you'd use Hubble to view the Moon).
But our lunar orbiters have spotted Apollo on the surface of the Moon. That's because they are so much closer.
You can see the landers and various hardware - and even the astronaut's tracks on the Moon.
New NASA pics show Apollo astronauts' footpaths on the moon
Let's do a rough calculation
Moon has angular diameter about 0.5 degrees and in kms it's 3500 km
Hubble has a resolution of 36,000 pixels to a degree so for the moon that's 18,000 pixels to cover the diameter of the moon, at 3500 km. I'm choosing Hubble because it's roughly comparable to the very best of our ground telescopes equipped with adaptive optics.
So each pixel is about 200 meters at the distance of the Moon. This is its "diffraction limit" - a limitation from pure physics based on the diameter of the telescope and the wavelength of light you use. There is no point in them trying to use a higher magnification - though you could do it in principle just by using powerful enough lenses or mirrors - but the resulting images would be fuzzy.
The only way to get to a higher resolution is to use a larger telescope (or several smaller telescopes acting together to simulate the effect of a larger mirror).
See The Diffraction Limit of a Telescopes
That's also why radio telescopes are so large - because the wavelength is larger - they need to use far bigger telescopes to get the same resolution.
So even Hubble, turned towards the Moon has no chance of seeing any of the Apollo landers - they are just below its best resolution.
As for ground based telescopes - then they have the problem of the Earth's atmosphere - so - though they can have larger mirrors than Hubble - and you can use several of them working together to emulate an even larger mirror - and can do adaptive optics also which to some extent helps to "untwinkle" the night sky - still - they aren't quite good enough yet to be able to spot Apollo on the Moon.
Indeed - they are still "chasing" Hubble, I think Hubble is still the best - except possibly when imaging the brightest stars using adaptive optics. And the James Webb telescope - though larger than Hubble, is optimized for infra red observation - and still won't have better resolution - it wouldn't be able to spot them either. High-resolution imaging with large ground-based telescopes
So - I don't think we have any upcoming telescopes either, on Earth or in orbit - that have much of a chance of spotting them. (Do correct me in the comments if you know of any that are!).
It looks so striking, e.g. the deep field images
Hubble Team Unveils Most Colorful View of Universe Captured by Space Telescope
You can zoom in and in on the image, seems, if you can see distant galaxies billions of light years away in such detail - why can't we see Apollo on the Moon?
But - galaxies are pretty huge things, the Moon is tiny in comparison. And Apollo is even tinier compared to the Moon.
Even zoom right in, then Apollo on the same scale would be far smaller than a single pixel in this image.
It's at least an order of magnitude too small - just a little bit below the visual resolution of Hubble (not that you'd use Hubble to view the Moon).
But our lunar orbiters have spotted Apollo on the surface of the Moon. That's because they are so much closer.
You can see the landers and various hardware - and even the astronaut's tracks on the Moon.
About the Author
Robert Walker
Writer of articles on Mars and Space issues - Software Developer of Tune Smithy, Bounce Metronome etc.Studied at Wolfson College, Oxford
Lives in Isle of Mull
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