Sirius
Collier's New Encyclopedia (1921)
in astronomy, the dog log star, by far the brightest fixed star in the sky. It is alpha Canis Major, situated a little below Orion, and is mythologically regarded as one of the hounds held in leash by Orion, Procyon in Canis Minor being the other. A A line drawn from the Plei-. ades through the three stars of Orion's belt will pass it closely; straight lines connecting it with Procyon and Betelgeuse will constitute a nearly equilateral triangle; and Aldebaran, Betelgeuse, Sirius, and Regel, all of the first magnitude, form a lozenge-shaped figure, with Orion's belt in the center. Ptolemy, in the 2d century, ranked Sirius among red stars; now it is white, and is a very brilliant object, its light being 324 times as great as that of a star of the sixth magnitude. It is about 1,000,000 times as far from us as the sun, and its mass is about 20 times as great. Viewed by the spectroscope, its chief lines are those of incandescent hydrogen, with feebler ones of sodium and magnesium; the metal mercury seems also to be present. Some irregular movements of Sirius led to the belief that a heavenly body existed near enough to produce a perturbation, and a son of Alvan Clark, of Boston (Mass.). discovered, on Jan. 31, 1862, what appears to be a planet revolving around Sirius as its sun, it is thought in about 49 years. The heliacal rising of Sirius varies in different latitudes, and the procession of the equinoxes makes it do so also in successive ages. When the heliacal rising of Sirius (called by the old Egyptians Sothes) took place, it indicated to them that the overflow of the Nile was at hand.
What Has Changed in the Last Century
Collier's in 1921 called Alvan Clark's 1862 discovery "what appears to be a planet revolving around Sirius as its sun." It is nothing of the kind: Walter Adams's 1915 spectrum showed the companion to be blazing hot yet tiny, and Sirius B is now the textbook white dwarf, roughly the mass of the Sun packed into a body the size of the Earth, its collapsed matter explained by quantum theory in the late 1920s. The orbital period of about 49 years given here has held up well (modern value near 50.1 years), but the other numbers have not: Sirius lies 8.6 light years away, some 540,000 times the Sun's distance rather than a million, and Sirius A is about twice the Sun's mass, not twenty times. Ptolemy's ranking of Sirius among the red stars, which puzzled the 1921 writer, is still unresolved and is usually put down to reddening when the star is low in the sky, or to a mistranslation, rather than to any real change in the star.
Written for this edition, 2026.