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youngyew Male
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  #9 Old 25-06-2007 Default

Originally Posted by tezuka87
If the sun blots out it would take 8 minutes for us to find out..this is cos it takes 8 minutes for the sun's light to reach earth. This also means that the sun we see is actually the sun as it was 8 minutes ago.

Similarly, the moon we see is the moon as it was 1 minute ago.
The light from moon should be about 1.2 to 1.3 seconds ago, as the moon's distance from earth is 360,000 km to 400,000 km while the speed of light is about 300,000 km/s.

Anyway, it's interesting to think about the speed of light in terms of interstellar distances. There's an interesting paragraph in Bill Bryson's book "A Short History of Nearly Everything" about Drake equation:

"... Unfortunately, space being spacious, the average distance between any two of these civilizations is reckoned to be at least two hundred light years, which is a great deal more than merely saying it makes it sound. It means, for a start, that even if these beings know we are here and are somehow able to see us in their telescopes, they're watching light that left Earth two hundred years ago. So they're not seeing you and me. They're watching the French Revolution and Thomas Jefferson and people in silk stockings and powdered wigs - people who don't know what an atom is, or a gene, and who make their electricity by rubbing a rod of amber with a piece of fur and think that's quite a trick. Any message we receive from these observers is likely to begin 'Dear Sire', and congratulate us on the handsomeness of our horses and our mastery of whale oil. Two hundred light years is a distance so far beyond us as to be, well, just beyond us."

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