There is some little interest in the Great Bear on account of the possibility of its being used as a kind of celestial time-keeper, and its easy recognition makes it all the more available. The line through α and β passes almost exactly through the pole. Now this line revolves of course with the constellation round the pole in 24 hours; in every such interval being once, vertical above the pole, and once vertical below, taking the intermediate positions to right and left between these times. The instant at which this line is vertical over the pole is not the same on any two consecutive nights, since the stars advance each day 4 minutes on the sun. On the 21st of March the superior passage takes place at 5 minutes to 11 at night; on the following night four minutes earlier, or at 9 minutes to 11. In three months the culmination takes place 6 hours earlier, or at 5 minutes to 5. In six months, i.e. on Sept. 22, it culminates at 10.55 in the morning, being vertically below the pole at the same hour in the evening. The following woodcut exhibits the positions of the Great Bear at the various hours of September 4th. It is plain from this that, knowing the day of the month, the hour of the night may be told by observing what angle the line joining α and β of this constellation makes with the vertical.
We have used the name Great Bear, by which the constellation is best known. It is one of the oldest names also, being derived from the Greeks, who called it Arctos megale (Ἄρκτος μεγάλη), whence the name Arctic; and singularly enough the Iroquois, when America was discovered, called it Okouari, their name for a bear. The explanation of this name is certainly not to be found in
Fig. 4.
the resemblance of the constellation to the animal. The three stars are indeed in the tail, but the four are in the middle of the back; and even if we take in the smaller stars that stand in the feet and head, no ingenuity can make it in this or any other way resemble a bear. It would appear, as Aristotle observes, that the name is derived from the fact, that of all known animals the bear was thought to be the only one that dared to venture into the frozen regions of the north and tempt the solitude and cold.
Fig. 5.
Other origins of the name, and other names, have been suggested, of which we may mention a few. For example, "Ursa" is said to be derived from versus, because the constellation is seen to turn about the pole. It has been called the Screw (Ἔλικη), or Helix, which has plainly reference to its turning. Another name is Callisto, in reference to its beauty; and lastly, among the Arabs the Great and Little Bears were known as the Great and Little Coffins in reference to their slow and solemn motion. These names referred to the four stars of each constellation, the other three being the mourners following the bearers. The Christian Arabs made it into the grave of Lazarus and the three weepers, Mary, Martha, and their maid.
Next as to the Little Bear. This constellation has evidently received its name from the similarity of its form to that of the Great Bear. In fact, it is composed of seven stars arranged in the same way, only in an inverse order. If we follow the line from β to α of the Great Bear to a distance of five times as great as that between these stars we reach the brightest star of the Little Bear, called the Pole Star. All the names of the one constellation have been applied to the other, only at a later date.
The new constellations were added one by one to the celestial sphere by the Greeks before they arranged certain of them as parts of the zodiac. The successive introduction of the constellations is proved completely by a long passage of Strabo, which has been often misunderstood. "It is wrong," he says, "to accuse Homer of ignorance because he speaks only of one of the two Celestial Bears. The second was probably not formed at that time. The Phenicians were the first to form them and to use them for navigation. They came later to the Greeks."