Fig. 424.
Fig. 425.
Fig. 426.
Whether the sun is actually moving in a straight line, or around some distant centre, it is impossible to determine at the present time. It is estimated that the sun is moving along his path at the rate of about a hundred and fifty million miles a year. This is about five-sixths of the diameter of the earth's orbit.
366. Star-Drift.—In several instances, groups of stars have a common proper motion entirely different from that of the stars around and among them. Such groups probably form connected systems, in the motion of which all the stars are carried along together without any great change in their relative positions. The most remarkable case of this kind occurs in the constellation Taurus. A large majority of the brighter stars in the region between Aldebaran and the Pleiades have a common proper motion of about ten seconds per century towards the east. Proctor has shown that five out of the seven stars which form the Great Dipper have a common proper motion, as shown in Fig. 427 (see also Fig. 420). He proposes for this phenomenon the name of Star-Drift.
Fig. 427.