When you look up into the night sky you can see forever. Assuming there arent clouds. And that you have infinitely sensitive eyes. Its a romantic idea but the fact is, on a perfect dark sky the human eye can only just make out a few objects at 11 million light years--and those objects are whole galaxies. On an imperfect night you can usually make 2 to 3 million light years. Galaxies again. In most cities you can only see a few thousand light years. Its pretty cool, dont get me wrong. Amazing really, from our mundane point of view. You can actually see back in time! Of course thats just a failure of our point of view. Everything we see happened in the past. That sun set? It actually happened well more than 8 minutes ago (not about 8 as you might expect. As the sun drops below the horizon, its light is refracted around the Earth so it appears higher in the sky than it is). Even the Moon is over a light second (about 1.28 light seconds) away. So the moon you see is over one second in the past. I do like the idea of looking into the infinite distance. The idea that if you wish upon a star, sorry that star is dead. But for most of us, no. Its not. That star is relatively nearby, on the Main sequence. Its probably still there. (There are a few notable exceptions, which will make spectacular shows when the light of their deaths get here.) So go ahead. Wish on a star. Odds are its still there. Of course, since its just a massive ball of nuclear fire, it wont actually help your wish. But it is there.
Posted on: Mon, 19 Jan 2015 01:04:42 +0000
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