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| 31 | STAR-STREAMS |
It is well to form some notion of what these displacements amount to. The star which appears to us to move faster than any other is an insignificant object in the southern sky far too faint to be visible without a telescope. This star traverses a space equal to the apparent diameter of the full moon in about two hundred years. If the majority of stars had speeds at all approaching this amount, the detection of their movements would not be difficult; but it is not so. Not one in seventy of the stars visible to the naked eye has so much as one fiftieth part of this speed, and for telescopic stars the proportion is much smaller. An average star might be expected to take say 50.000 years to move over a space in the sky equal to the moon’s diameter. Of course it is on account of the excessive remoteness of the stars that their motions appear so small; judged by terrestrial standards the real speeds are prodigious. The average linear velocity of a star is about 34 kilometres per second.
From the time when the first measures were made of the proper motions, up to near the close of the nineteenth century attention was principally, almost exclusively, devoted to one fascinating problem, the determination of the motion of our own system with respect to the stars. This, and not the study of the relations of the stellar motions to one another, was the main subject of investigation. When the statistics are collected and examined, it is noticed that in the main the stars are moving towards a point of the heavens in or near the constellation Canis Major. The motions of the individuals vary widely, but if the mean of a number of stars is considered, it is practically always possible to detect this tendency. It is as though we were looking at a swarm of gnats, the individuals buzzing in all directions, but the swarm as a whole proceeding steadily in one particular direction. Now in sidereal astronomy we leave behind our ordinary standards of rest; there are no fixed points; the relativity of all motion insists on being recognised. It is immaterial whether, the solar system being at rest, the star-swarm moves towards Canis Major, or whether, the star-swarm being at rest, the solar system moves in the opposite direction towards Lyra; the apparent motion of the stars is the same in either case, and we have no means of testing, or recognising, or even conceiving absolute rest or absolute motion. The second point of view, that the phenomenon
