The James Webb Space Telescope’s First Deep Field image covers a patch of sky approximately the size of a grain of sand held at arm’s length by someone on the ground – and shows flecks of light representing some 5,500 galaxies according to astronomers. Each of those early galaxies has about 10 billion stars (2024 update: it now appears that even the earliest galaxies, such as JADES-GS-z14-0, are as large as some of the current ones, in other words they have hundreds of billions of stars).
How many such grains of sand at arm’s length would it take to cover the whole sky? One guy worked it out as 811,800,000,000 large grains (0.8 trillion) and 81,180,000,000,000 (81.8 trillion) small ones. And behind each grain, thousands of galaxies, each with billions of stars, and each star has many planets, any of which could harbor life.
So there is practically an uncountable number of galaxies in the universe, and centillions of stars and planets.
How many stars in our spiral galaxy, the Milky Way? Estimates vary from 100 to 400 billion (we can’t tell exactly because we are facing the galaxy side-on). You can see our galaxy very clearly if you look up at a moonless night sky in the Outback, which is one of the reasons I love traveling to remote, unpopulated places like the Outback.
How far is the next galaxy? The nearest galaxy is Canis Major Dwarf. At the speed Voyager is traveling (~16 km per second) it would take 749 million years to get there, or 25,000 years at the speed of light.
Life is probably common in the universe, a reassuring thought as human beings drive thousands of species to extinction.
