I don’t understand Lunar Laser Ranging experiment. Are the mirrors perpendicular?

[Myth27]

You can shine a laser at retroreflectors at the moon and get some photons back to earth. Can you do this from any point of the earth surface? If so how is it possible? Shouldn’t the retroreflector be precisely perpendicular to you? Does it work because the moon always shows the same face to earth ?

[Jasdoif]

Shouldn’t the retroreflector be precisely perpendicular to you?No; this is exactly what retroreflectors (https://en.wikipedia.org/wiki/Retroreflector) are for. Basically, the inside of a retroreflector reflects light multiple times, in a way that sends it out in the reverse of the direction it came in with.

[Mastikator]

https://upload.wikimedia.org/wikipedia/commons/thumb/2/21/ALSEP_AS15-85-11468.jpg/1024px-ALSEP_AS15-85-11468.jpg

They aren't just flat mirrors. They reflect directly back from most angles. Similar to how road signs work always reflect the light from your car back at the car.

[Rockphed]

In radar the equivalent object is called a "corner reflector" because it is formed from several sheets of metal formed into a corner. However light hits the reflector is gets reflected back the way it came.

[Myth27]

Oh cool, thanks guys!