“We had the sky up there, all speckled with stars, and we used to lay on our backs and look up at them, and discuss about whether they was made or only just happened.” — from The Adventures of Huckleberry Finn by Mark Twain.
If you look up at the sky at night, how many stars do you think you see? Perhaps you hear the voice of Carl Sagan from his television series Cosmos intoning in a way that inspired so many of us: “There are in fact 100 billion galaxies, each of which contain something like 100 billion stars. Think of how many stars, and planets, and kinds of life there may be in this vast and awesome universe.”
You actually see a lot fewer stars than billions, or even millions.
In the second century CE, the Greco-Roman astronomer Ptolemy created a definitive guide to the heavens, the Almagest, which listed the names and locations of only 1028 stars. In 1602 in Denmark, Tycho Brahe, perhaps the all-time best naked-eye astronomer, listed 1000 stars in his guide, the Progymnasmata. No one has counted since, but the estimate of the stars visible to the bare eye in a given place and night has doubled to 2000 — far short of a billion.
I know this, and when I look at the sky, I see a lot fewer due to big-city light pollution, yet it feels like billions. Why? Because I know they’re there.
In 1610, Galileo Galilei became the first person to peer through a telescope at the night sky. He saw “stars in myriads which have never been seen before, and which surpass the old previously known stars in number more than ten times.” He saw that the mysterious, murky Milky Way was not “celestial exhalations” as some had speculated but in fact “a mass of innumerable stars planted together in clusters.”
The Milky Way contains a hundred billion stars — and there are billions of galaxies. The Hubble Space Telescope focused deep on a speck of the sky in December, 1995, and photographed galaxies in all shapes and colors, several hundred of them never seen before.
The only stars we see with our bare eyes at night are in our own galaxy, the Milky Way — but even if we didn’t have telescopes peering ever deeper into the sky, the other galaxies would still be there, billions upon billions of stars indeed, out of sight but not out of mind.