If you ever want to ponder the vastness of the universe, try this: Look up into a dark, starry night sky, then hold out your hand at arm’s length in front of your face. Now look at the fingernail on your little finger. That tiny area is covering up millions of galaxies — and perhaps tens of millions. Yet every galaxy is enormous. It spans thousands to millions of light-years, and contains millions to trillions of stars. The number of galaxies you’re covering up is uncertain because the number of galaxies in the universe is uncertain. There are just so many, and many of them are so faint, that we can’t count them all. Instead, astronomers estimate the total. More than a decade ago, Hubble Space Telescope spent weeks looking at a tiny patch of sky. Based on the number of galaxies in that patch, astronomers estimated the total number at about 200 billion. Later, though, another team said there should be 10 times more galaxies — about two trillion in all. But last year, one more study, bas
