How many stars are there in the universe? No one knows, of course, but Dr. Carl Sagan — in his popular 1980s television series, Cosmos — famously said that there are “more stars in the universe than there are grains of sand on all the beaches on Earth.”
Now that’s a lot of stars! But is it true?
Estimating the number of sand grains is a bit tougher than estimating the number of stars, but it has been done.
For example, Jason Marshall, aka the Math Dude, estimates that there are about 700 trillion cubic meters of beach on Earth, which works out to around 5 billion trillion sand grains. That’s a five followed by 21 zeroes!
So, is it possible that there are more stars than that? Well, astronomers figure that at least 200 billion stars populate our own Milky Way Galaxy.
Since we’ve long believed that our universe contains a hundred billion or so galaxies, we can conclude that there should be some 20 billion trillion stars (that’s a two followed by 22 zeroes) — four times as many as grains of sand.
As impressive as this number may sound, it could be rather low. Recent Hubble Space Telescope photographs suggest to astronomers that their estimates of the number of galaxies in the universe may be too small by a factor of 10.
A factor of 10!
If correct, this means that there could be as many as a trillion galaxies in the universe and, contained within them, a total of some 200 billion trillion stars. That’s a two followed by 23 zeroes!
Of course, this is all just a guess, but the numbers are based on what we currently observe and measure.
So how many of those stars can we see with our own eyes on a clear, dark night? Most stargazers would say they can see billions, but this, too, is just a guess. To be more precise, why not count them?
Now before you call the authorities to have me committed, try it yourself the next time you’re under a clear, dark sky. It really isn’t all that difficult or time-consuming; the only tools you’ll need are a cardboard tube from a roll of bathroom tissue, a pen, a notepad and perhaps a calculator. And, of course, a nice, clear, dark sky.
Place the tube up to your eye and aim it skyward. Holding it still, count the stars you see within and record that number on the notepad. Now, do the same for seven additional spots randomly scattered around the entire sky. When you’re finished, add those eight numbers together and multiply that sum by 10.
That’s it. That’s the approximate number of stars you can see with your eye from that location on that night. Surprised?
If you thought you could see billions of stars, you going to be in for quite a shock because even on the clearest and darkest of nights, the very best eyes can see only two or three thousand stars at most.
Yes, folks, we’re part of a truly immense universe, but most of it is far beyond our ability to perceive or comprehend!
— Dennis Mammana is an astronomy writer, author, lecturer and photographer working from under the clear dark skies of the Anza-Borrego Desert in the San Diego County backcountry. Contact him at firstname.lastname@example.org and connect with him on Facebook: @dennismammana. Click here to read previous columns. The opinions expressed are his own.