There's a whole universe out there...

What do you see when you look up at the night sky?

Well, I suppose it depends on where you are - how much light pollution you live with, and what the phase of the moon is.

But, really? What do you see?

If your answer is "Not much, really", my first suggestion is that you go up on top of a mountain away from the city, or out into the desert on a really clear, moonless night. Then answer the question again. If you're lucky, you'll see something like this:

I imagine your first answer will be, "Stars. Lots of stars." If you're a fan of Kubrick's "2001: A Space Odyssey", what you say to yourself as you look up might be, "It's full of stars." And that might not be a bad answer.

Not that the sky is really "full of stars", although it might seem like that under the right viewing conditions. But the truth is that, for all that is out there, the universe seems to be mostly empty space. One article at "How Stuff Works" says it like this:

A cubic light year contains about 1E+48 cubic meters. So all of the matter in the universe would fit into about 1 billion cubic light years, or a cube that's approximately 1,000 light years on each side. That means that only about 0.0000000000000000000042 percent of the universe contains any matter. The universe is a pretty empty place!

Those are pretty difficult numbers to comprehend (especially for those of us who are mathematically challenged), but even I can see that the last number there - the one with the decimal point and all those zeroes - means that the amount of matter in the universe is vanishingly small.

But, even at that, there are (to misquote Carl Sagan) "billions and billions" of stars just in our own galaxy. The Wikipedia article on our galaxy (the Milky Way) speculates that there are between 200 billion and 400 billion stars in our galaxy. Of course, there are problems with using Wikipedia as a research source, but it isn't a bad place to begin, to start figuring out the lay of the land. An article at Science.com gives a lower estimate of about 100 billion stars in our galaxy. How Stuff Works (yeah, them again) ( http://science.howstuffworks.com/milky-way5.htm ) puts its estimate at about 200 billion stars - the low end of Wikipedia's estimate. A much, much larger estimate appears in an article at Huffington Post, at about a trillion stars - just in one galaxy. Multiply any of those, roughly, by the number of galaxies estimated to exist in the universe - and there again, the numbers vary. Space.com says 100 billion to 200 billion. Universe Today gives the same rough estimate but then cites German research that puts the number at more like 500 billion.

In other words, there are a lot of galaxies out there, made up of an unimaginable number of stars. Of course, we can't see all of those, even in places where the seeing is good. With the unaided eye, so says the One Minute Astronomer, where the seeing is good, you an see around 2,000 to 2,500 stars in the sky on a typical night. But those are only the ones on the side of the Earth that is in darkness at any one time, so it makes sense to double that number to know how many stars it is possible to see from earth with the unaided eye. Those all, by the way, are stars that belong to our own galaxy. The same site points out that with just a pair of binoculars - without needing even a rudimentary telescope - that number increased to around have a million stars that can, potentially, be seen from earth, again, all inhabitants of the Milky Way. Even without those binoculars, thought, you an see one of our galactic neighbors, the Andromeda Galaxy, which has an estimated 500 billion stars of its own. But, without the aid of a powerful telescope, you'll only see Andromeda as a pinpoint of light.

All of that - all of those billions and billions of galaxies, each containing billions and billions of stars - and they would all fit in a miniscule fraction of one percent of all the space available in the universe. It's a mind-boggling thought, isn't it?

But, as mind-boggling as it is, every time I go out to look at the stars, I'm struck by the thought that all of those pinpricks of light, some representing only one star, or maybe two in a binary system, and some representing entire galaxies, are places, just like this rock, this Earth, all traveling through space because they - and we - are moving through space in several different ways all the time.

As far as I'm concerned, everyone needs to have their mind boggled every once in a while. So, my advice to you is to go out on the next clear, moonless night, get as far away from the city lights as you can, and look up. See what the universe has to offer. And then just think about those places out there. It'll be good for you. It might even be fun.