The great star is worthy of all its fame, not only by its magnificent beauty, but by the revelations which modern science has afforded us concerning it. While not comparable in actual luminosity with Rigel, Canopus, or even Arcturus, it immensely outshines the best of them to our eyes because of its relative nearness. Its distance is only about 50,000,000,000,000 miles (parallax 0″.37), so that it is really one of the nearest stars in the sky. Light requires about nine years to come to us from Sirius. Outshining the sun at least thirty times, it is so bright, even at that distance, that a special rank has been given to it in stellar photometry. Formerly all very bright stars were ranked as of the first magnitude, but greater exactness is now employed, the naked-eye stars being divided among eight magnitudes, running from 6 up to -1. Thus the faintest star visible to the naked eye is of magnitude 6; a star 2.51 times brighter is of magnitude 5; a star 2.51 times brighter than that is of magnitude 4, and so on up to magnitude 1. A star 2.51 times brighter than magnitude 1 is of magnitude 0; and one 2.51 times brighter than the 0 magnitude is of magnitude -1, a degree of brilliance which is attained by Sirius alone. In fact, Sirius exceeds magnitude -1, its real rank being -1.6. On the same scale the magnitude of the sun would be -26.3. The standard first magnitude s usually taken as being represented by the star Altair, although that star is not _exactly_ of that magnitude. As a ready rule it may be said that each magnitude is two and a half times brighter than the next below it, and a difference of six magnitudes corresponds to an increase of one hundred times in brilliance. Sirius is about ten times as bright as Altair. While, if _seen from the same distance_, Sirius would appear at least thirty times as bright as the sun, at our actual distance from both the light received from the sun is to that received from Sirius in the ratio of about 7,000,000,000 to 1. While by no means the largest sun in the universe, Sirius is the largest sun in our part of space, and some indications have been detected that it may, to a certain extent, control the motion of the solar system. In other words, our sun and some of the nearer stars appear to form a group, or family, of which Sirius is probably the chief.