Originally posted by blocula
Go outside on a clear day and try looking at the sun,its so blindingly bright we cant even look at it with our eyes and theres just no way that i'm
going to believe its really 865,000 miles across and 93,000,000 miles away...
The Sun is big, really, really big. Almost all of the matter that makes up our solar system is contained within the Sun, that's why it can keep
things that are so far away in its orbit and the reason it shines so amazingly brightly is because all of that matter is burning, and not burning like
coal, burning like a nuclear explosion...in fact, I shouldn't say "like" a nuclear explosion, because that's what the Sun is, a gigantic nuclear
explosion that has been exploding for almost 5 billion straight years and is due to keep exploding for another 5 billion more.
I know, it's hard to fathom primal forces so vast and so powerful, but that's what is going on.
If the suns gravity keeps the earth in orbit,whats holding the sun within its orbit?
In orbit around the rest of the Milky Way Galaxy? Well, the gravity of the rest of the galaxy, of course. There's between 200 billion and 400
billion stars in the Milky Way, and lot more dark matter besides that. The combined effects of the gravity of all these stars and the dark matter
keep the whole thing together.
Why do we only see a few hundred stars at night? why isnt the night sky filled with millions of stars? why isnt the sky at night aglow like
Have you ever been out at night in the countryside where there's no light pollution? You will see many thousands of stars at night, not just a few
hundred. We can see only those stars that are close enough and bright enough that their light doesn't become too dim by the time it reaches Earth.
With more sensitive tools, very powerful telescopes, we can see many more stars than our human eyes are capable of.
Maybe it's hard for you to conceive of these sizes and distances, which isn't surprising because they are all on scales that are pretty far beyond
what our brains were designed to comprehend. Our brain and sensory organs evolved to help us survive in the middle-scale environment of hunting,
gathering and keeping alive in the African wilderness. At that scale the largest distances we need to fathom are measured in the tens of miles, or
maybe hundreds for a nomadic culture. The biggest single thing we'd ever see that is close enough for us to really comprehend its size is a big
mountain, valley or plain. A glorious vista on Earth is the biggest view we'd ever need to see and understand, so to our brains that's about as big
as we can really imagine. Everything beyond that is a bit hard for us to make sense of. Yes, we all can see the moon most every night, a whole other
world -- a pretty big one, nearly as big as Mercury, actually -- but our moon is far enough away that it looks pretty small, so until we really
understood what it was we didn't have to comprehend it at those scales.