Of the billions and billions of stars in the heavens, only about 6,000 can be seen from the earth without a telescope. And about a quarter of these 6,000 stars cannot be seen from most lands north of the equator.
Some of the stars that we can see look much brighter than others. Scientists call the brightness of a star its magnitude. A star with a magnitude of one is twice as bright as a star with a magnitude of two, a magnitude-two star is twice as bright as a magnitude-three star, and so on.
Stars with a magnitude of more than six can be seen only with a telescope. But telescopes can see stars with a magnitude of 21! A magnitude-one star is more than a million times as bright as a magnitude-21 star!
There are only 22 stars in the sky with a magnitude of one!