CANIS MAJOR ("Great Dog"), in astronomy, a constellation placed south of the Zodiac, just below and behind the heels of Orion. Canis minor, the "little dog," is another constellation, also following Orion and separated from Canis major by the Milky Way. Both these constellations, or at least their principal stars, Sirius in the Great Dog and Procyon in the Little Dog, were named in very remote times, being referred to as the "dogs of Orion" or in equivalent terms. Sirius is the brightest star in the heavens; and the name is connected with the adjectives and , scorching. It may possibly be related to the Arabic Siraj, thus meaning the "glittering one." Hommel has shown that Sirius and Procyon were "the two Si'ray" or glitterers. It is doubtful whether Sirius is referred to in the Old Testament. By some it has been identified with the Hebrew mazzaroth, the Lucifer of the Vulgate; by others with mazzaloth, the duodecim signa of the Vulgate; while Professor M.A. Stern identifies it with the Hebrew kimah, which is rendered variously in the Vulgate as Arcturus, Hyades and Pleiades.  The inhabitants of the Euphrates valley included both constellations in their stellar system; but considerable difficulty is encountered in the allocation of the Babylonian names to the dominant stars. The name kak-ban, which occurs on many tablets, has been determined by Epping and Strassmaier, and also by Jensen and Hommel, as equivalent to Sirius; etymologically this word means "dog-star" (or, according to R. Brown, Primitive Constellations, "bow-star"). On the other hand, Kaksidi or Kak-si-sa, meaning the "leader," has been identified by Sayce and others with Sirius, while Hommel regards it as Procyon. The question is mainly philological, and the arguments seem inconclusive. We may notice, however, that connexions were made between Kaksidi and the weather, which have strong affinities with the ideas expressed at a later date by the Greeks. For example, its appearance in the morning with the Sun heralded the "north winds," the or aquilones etesiae, the strong and dangerous north-westerly winds of Greece which blow for forty days from the rising of the star; again, when Sirius appeared misty the "locusts devour." Sirius also appears in the cosmogony of Zoroaster, for Plutarch records that Ormuzd appointed this star to be a guard and overseer in the heavens, and in the Avesta we find that Tistrya (Sirius) is "the bright and happy star, that gives happy dwelling." With the Egyptians Sirius assumed great importance. Appearing with the Sun when the Nile was rising, Sirius was regarded as a herald of the waters which would overspread the land, renewing its fertility and promising good harvests for the coming season. Hephaestion records that from its aspect the rise of the water was foretold, and the Roman historian Florus adds that the weather was predicted also. Its rising marked the commencement of their new year, the annus canarius and annus cynicus of the Romans. It was the star of Sept or Sothis, and, according to one myth, was identified with the goddess Hathor - the Aphrodite of the Greeks. It was the "second sun" of the heavens, and according to Maspero (Dawn of Civilization, 1894) "Sahu and Sopdit, Orion and Sirius, were the rulers of this mysterious world of night and stars."
The Greeks, borrowing most of their astronomical knowledge from the Babylonians, held similar myths and ideas as to the constellations and stars. Sirius was named (the dog) and , the star; and its heliacal rising was associated with the coming of the dry, hot and sultry season. Hesiod tells us that "Sirius parches head and knees"; Homer speaks similarly, calling it , the evil star, and the star of late summer , the rainy and stormy season. Procyon was so named because it rose before . The Euphratean myth of the dogs has its parallel in Greece, Sirius being the hound of the hunter Orion, and as recorded by Aratus always chasing the Hare; Pindar refers to the chase of Pleione, the mother of the Pleiads, by Orion and his dogs. Similarly Procyon became Maera, the dog of Icarius, when Boötes became Icarius, and Virgo his daughter Erigone.
The Romans adopted the Greek ideas. They named the constellation Canis, and Sirius was known as Canis also, and as Canicula. Procyon became Antecanem and Antecanis, but these names did not come into general use. They named the hottest part of the year associated with the heliacal rising of Sirius the Dies caniculares, a phrase which has survived in the modern expression "dog-days"; and the pestilences which then prevailed occasioned the offering of sacrifices to placate this inimical star. Festus narrates, in this connexion, the sacrificing of red dogs at the feast of Floralia, and Ovid of a dog on the Robigalia. The experience of the ancient Greeks that Sirius rose with the Sun as the latter entered Leo, i.e. the hottest part of the year, was accepted by the Romans with an entire disregard of the intervening time and a different latitude. To quote Sir Edward Sherburne (Sphere of Manilius, 1675), "The greater part of the Antients assign the Dog Star rising to the time of the Sun's first entering into Leo, or, as Pliny writes, 23 days after the summer solstice, as Varro 29, as Columella 30.  ...At this day with us, according to Vulgar computation, the rising and setting of the said Star is in a manner coincident with the Feasts of St Margaret (which is about the 13th of our July) and St Lawrence (which falls on the 10th of our August)."
Sirius is the most conspicuous star in the sky; it sends to the earth eleven times as much light as Aldebaran, the unit standard adopted in the revised Harvard Photometry; numerically its magnitude is -1.6. At the present time its colour is white with a tinge of blue, but historical records show that this colour has not always prevailed. Aratus designated it , many coloured; the Alexandrian Ptolemy classified it with Aldebaran, Antares and Betelgeuse as , fiery red; Seneca describes it as "redder than Mars"; while, in the 10th century, the Arabian Biruni termed it "shining red." On the other hand Sufi, who also flourished in the 10th century, pointedly omits it from his list of coloured stars. The question has been thoroughly discussed by T.J.J. See, who shows that Sirius has shone white for the last 1000 to 1200 years.  The parallax has been determined by Sir David Gill and W.L. Elkin to be 0.37"; it is therefore distant from the earth over 5 10^13 miles, and its light takes 8.6 years to traverse the intervening space. If the Sun were at the same distance Sirius would outshine it 30 times, the Sun appearing as a star of the second magnitude. It has a large proper motion, which shows recurrent undulations having a 50-year period. From this Bessel surmised the existence of a satellite or companion, for which C.A.F. Peters and A. Auwers computed the elements. T.H. Safford determined its position for September 1861; and on the 31st of January 1862, Alvan G. Clark, of Cambridgeport, Mass., telescopically observed it as a barely visible, dull yellow star of the 9th to 10th magnitude. The mean distance apart is about 20 astronomical units; the total mass of the pair is 3.7 times the mass of the Sun, Sirius itself being twice as massive as its companion, and, marvellously enough, forty thousand times as bright. The spectrum of Sirius is characterized by prominent absorption lines due to hydrogen, the metallic lines being weak; other stars having the same spectra are said to be of the "Sirian type." Such stars are the most highly heated (see Star).
Procyon, or a Canis minoris, is a star of the 2nd magnitude, one-fifth as bright as Sirius, or numerically 0.47 when compared with Aldebaran. It is more distant than Sirius, its parallax being 0.33"; and its light is about six times that of the Sun. Its proper motion is large, 1.25", and its velocity at right angles to the line of sight is about 11 m. per second. Its proper motion shows large irregularities, pointing to a relatively massive companion; this satellite was discovered on the 13th of November 1896 by J.M. Schaeberle, with the great Lick telescope, as a star of the 13th magnitude. Its mass is equal to about that of the Sun, but its light is only one twenty-thousandth.
 See G. Schiaparelli, Astronomy in the Old Testament (1905).
 For other values of the interval between the summer solstice and the rising of Sirius, see Smith's Dict. of Greek and Roman Antiquities.
 See Thomas Barker, Phil. Trans., 1760, 51, p. 498, for quotations from classical authors; also T.J.J. See, Astronomy and Astrophysics. vol. xi. p. 269.
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)