Astronomers can use the Hubble Space Telescope to view galaxies near the edge of the observable universe the region of space from which light has had a chance to reach us within the last 13.77 billion years. By examining a very tiny portion of the sky, counting up the number of galaxies visible in that region, and then multiplying that number to account for all the regions of the sky, astronomers estimate the number of galaxies in the observable universe. The best estimate from a 1999 study set that number at about 125 billion galaxies, but a 2013 study indicated that there are 225 billion galaxies in the observable universe.

read more How many galaxies are there in the universe? | Sky & Telescope.