Could a mirror in space let us photograph Earth's past?

[atarah]

TL;DR

can you theoretically put a mirror in space, take a photo of earth/dirts reflection and see it in the past?

can you theoretically put a mirror in space, take a photo of earth/dirts reflection and see it in the past?

 

[Nugatory]

We don’t even need a mirror to produce that effect. When I see a fly land on a table 3 meters away…. The fly actually landed about 10 nanoseconds before I saw it land, because that’s how long it took the light to travel the 3 meters between the table and my eye. The same thing would happen if we were using a camera instead of a human eye to form the image.

And yes, sending the light on a circuitous path with one or more mirrors allows us to introduce yet more lag between event and eye. In practice however, we’re not going to be able to get more than a tiny fraction of a second of additional delay that way.

 

[jbriggs444]

Summary: can you theoretically put a mirror in space, take a photo of earth/dirts reflection and see it in the past?

Unless the mirror is already there, getting it set up will require so much time that you'll not see any farther into the past than when you launched it.

So if you are planning on getting some long distance images of the grassy knoll at a particular historically relevant moment, you are out of luck.

 

[anorlunda]

How about this view? It looked back 3 seconds in history.

 

[sophiecentaur]

Summary: can you theoretically put a mirror in space, take a photo of earth/dirts reflection and see it in the past?

can you theoretically put a mirror in space, take a photo of earth/dirts reflection and see it in the past?

Your bathroom mirror will give you a delay of ten nanoseconds or so. that would be a start!