Astronomers estimate that there are between 10 sextillion and 1 septillion stars in the visible Universe. This is a huge number. The number (an estimate) of galaxies in the universe is multiplied by the average amount of stars in a galaxy to get this approximate number. Depending on atmospheric conditions, 2500 to 3000 stars can be seen at night from Earth without ocular aid. The brightness of a star is called its magnitude. The brighter the star, the lower the number of magnitude. Betelgeuse and Aldebaran are two of the brightest stars in our heavens. They are about first magnitude stars.