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I saw a passage in my son's homework book, constructing a scenario in which a person standing on a planet 65 million light years away from Earth, with an extremely powerful telescope pointed at Earth, would be able to see the dinosaurs.

I understand the time reference, since the dinosaurs purportedly lived on the earth 65 million years ago. Does this really happen though? Does looking at faraway objects show past versions of that object?

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  • $\begingroup$ Even when you look at the clock in your room show the past version of the time $\endgroup$
    – user12195
    Commented Sep 13, 2012 at 7:22

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Yes, that's true, though whether you could actually see dinosaurs is debatable because from 65 million light years away they'd be pretty small :-)

The reason is very simple. When you look at a dinosaur you're seeing the light reflected from the dinosaur's skin. That light travels at a finite speed, so it takes a finite time to get from the dinosaur's skin to you. If you're a light year away from the dinosaur what you're seeing is the light reflected off the dinosaur's skin a year ago.

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    $\begingroup$ I would like to just point out that there is a subtlety to do with even establishing what the relative times of two spatial locations are --- in our universe this is do-able because of the big bang, which effectively provides a synchronisation pulse for everyone to "start their clocks". In the theory of general relativity, there is no natural "foliation" (synchronisation) independent of the geometry. $\endgroup$
    – genneth
    Commented Sep 13, 2012 at 8:43
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To The Star

by Mihai Eminescu, 1886

To the star up in ethereal heights
There's a path so far to stray,
Thousands of years might have its lights
Been wandering 'til today.

Maybe it perished long ago
On its way down through blue space,
This moment yet you come to know
Its shine upon your face.

The icon, gently soaring high,
Of that star now long since dead:
Could never spot it while alive,
Now gone - we see it yet.

Alike when our desire grown old
And lost in deepest night,
The light of faded love now cold
Still reaches our sight.

(Transl. by Alfred W. Tüting 1994 © All rights reserved)

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