If I point my laser pointer at the Moon, why don't I see a spot?
Because the luminosity of your laser beam (a fraction of a watt) is far too low to allow enough photons to make the trip, and then get reflected from a kilometer-sized spot from a low reflectivity surface, and then return through our atmosphere to your eye. This can be done, and is routinely done, using a powerful 100+watt laser beam attached to a large research-grade telescope. The laser light travels from here to the moon and is reflected back to the telescope using the Apollo laser retro-reflectors (see below) that were left on the surface in the early 1970's. With these reflectors, we can determine that the Moon is pulling away from Earth at about 1.3 centimeters each year.
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