The star that you see the brightest in the sky is not the brightest. And the star you have just seen is dim, don’t think it’s “darker” than the star you think is the brightest. The visibility of a star to your eye depends on two factors: how bright the star itself is and whether it is far away or near the earth. Looking at the sky, you must think there are many stars that your eyes can see. You still use the phrase “countless numbers” to denote the stars you see in the sky. The number of stars you see with the naked eye is not “countless numbers,” but only about 6000 stars. More than a third of these are in the southern hemisphere, so it’s not visible in the northern hemisphere.
More than two thousand years ago, Greek astronomers classified the stars according to their luminosity. Until the date of the telescope making, the stars were ranked as six brightest and six faintest. Stars are dimmer than six grades, which cannot be seen with the naked eye, but do not say that they do not exist because they cannot see. Today with modern telescopes, stars can be classified according to their luminosity into twenty-one grades. Each rank must be separated by two and a half times of the next rank. There are 22 brightest stars. And Sirius is the brightest of these 22 stars. It has a luminosity of 1.6, which means that Sirius is 100 times brighter than the faintest star visible to the naked eye. The number of stars increases gradually as we go from lightest to dimmest. The apex is 22 brightest, and the base is … 1 billion dull stars.