Amazing Galaxy Stuff

A few months ago, before all the leaves fell from the trees and this ridiculously cold weather moved in, Trish and I were sitting on the deck, looking at the stars. I decided to take a few photos of the night sky with my iPhone, using night mode. The photos came out better than I expected (see the first photo).

What I like about this photo is that you can clearly see a portion of our galaxy, the Milky Way. It's the whitish blur from the lower left to the upper right. And of course all the closer stars dotting the sky are also part of the Milky Way galaxy (the orange blobs on the bottom and left are trees). Nothing brings out our sense of awe more than staring up at the vastness of space, right?

Here's a bit more information about the galaxy we inhabit. First, you may know galaxies are huge clusters of stars, bound together by gravity. According to current models, galaxies formed in the early stages of the universe, following the Big Bang. Our Milky Way is called a spiral galaxy because the stars are rotating around a dense center, forming spiral arms that look a bit like a pinwheel. The galaxies we've observed contain, on average, about 100 million stars each. BUT, this is just an average, and the variation is huge. Some dwarf galaxies contain less than a thousand stars, and some supergiant galaxies can contain a hundred trillion stars. Uh, this number makes my head spin. It's beyond comprehension.

Our Milky Way galaxy has at least a thousand times more stars than the average, containing somewhere between 100 and 400 billion stars. Our sun (sometimes called Sol or Helios) is, of course, one of them.

Let's consider the dimensions of the Milky Way. A light year is the distance light travels in one year in the vacuum of space: 186,000 miles per second, or about 300,000 km per second. Light is pretty freaking fast, so a light year is pretty freaking far.

Like many galaxies, the Milky Way is shaped kind of like a disc. The disc is about 87,000 light years across. However, from top to bottom, it is only about 1,000 light years deep. And we (meaning Earth and the rest of our solar system) are about 27,000 light years out from the galaxy's center.

One last tidbit of info to blow your mind. Our galaxy is obviously unimaginably large. However, scientists estimate there are between 200 billion and 2 trillion galaxies within the observable universe.

Oh... in case you're wondering, the observable universe is a sphere with Earth at the center, and it includes everything we can see. In other words, every object close enough to us that light from the object has had time to reach Earth since the original expansion of the universe. This is not limited by our technology or telescopes, it is limited by the speed of light. Undoubtedly, there is much beyond the observable universe that we cannot see, simply because the light has not yet reached us.

Just for kicks, the second image is a set of photos, taken by the Hubble telescope, of a few of the gazillion other galaxies out there in space.

Photo Credits:
- Night sky - Stan C. Smith
- Collection of galaxy photos - NASA, ESA, ADAM G. RIESS (STSCI, JHU), Public domain, via Wikimedia Commons