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Q & A: Mirror to the past

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Most recent answer: 10/22/2007
Q:
if you were able to make a very big mirror and send it far far very far out into space would it be possible to view the earth with a very powerful telescope from earth and would we be seing the past???
- neil
london/ uk
A:
Yes, you would. Light travels at a speed of about 186,000 miles per second. For every 186,000 miles away you send your mirror, you can see something two seconds earlier. Send it far enough away, and you can see stuff that happened longer in the past.

Two limitations, however:

1) If the mirror is far enough away and not big enough, your telescope will not be able to distinguish close objects. A big mirror helps (but you have to keep your mirror all at the same distance, otherwise you get a mixture of times).

2) You cannot see anything earlier than when you sent your mirror up. In fact, you usually will get such a small glimpse into the past it may not be worth the effort (videotape is a cheaper way to preserve past events).

3) And then there are clouds, buildings, the sun, and other stuff to get in the way.

Tom

(published on 10/22/2007)

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