From Orion Magazine:
We call our galaxy the Milky Way. There are at least 100 billion stars in it and our sun is one of those. A hundred billion is a big number, and humans are not evolved to appreciate numbers like that, but here’s a try: If you had a bucket with a thousand marbles in it, you would need to procure 999,999 more of those buckets to get a billion marbles. Then you’d have to repeat the process a hundred times to get as many marbles as there are stars in our galaxy.
That’s a lot of marbles.
So. The Earth is massive enough to hold all of our cities and oceans and creatures in the sway of its gravity. And the sun is massive enough to hold the Earth in the sway of its gravity. But the sun itself is merely a mote in the sway of the gravity of the Milky Way, at the center of which is a vast, concentrated bar of stars, around which the sun swings (carrying along Earth, Mars, Jupiter, Saturn, etc.) every 230 million years or so. Our sun isn’t anywhere near the center; it’s way out on one of the galaxy’s minor arms. We live beyond the suburbs of the Milky Way. We live in Nowheresville.
But still, we are in the Milky Way. And that’s a big deal, right? The Milky Way is at least a major galaxy, right?
Not really. Spiral-shaped, toothpick-shaped, sombrero-shaped—in the visible universe, at any given moment, there are hundreds of thousands of millions of galaxies. Maybe as many as 125 billion. There very well may be more galaxies in the universe than there are stars in the Milky Way.
So. Let’s say there are 100 billion stars in our galaxy. And let’s say there are 100 billion galaxies in our universe. At any given moment, then, assuming ultra-massive and dwarf galaxies average each other out, there might be 10,000,000,000,000,000,000,000 stars in the universe. That’s 1.0 X 10 to the twenty-second power. That’s 10 sextillion. Here’s a way of looking at it: there are enough stars in the universe that if everybody on Earth were charged with naming his or her share, we’d each get to name a trillion and a half of them.
More here.