CHAPTER XL.
THE FIXED STARS.
FIXED STARS—MAGNITUDE OF THE STARS—CONSTELLATIONS—DESCRIPTIONS OF THE ZODIACAL CONSTELLATIONS—NORTHERN AND SOUTHERN STAR GROUPS—DISTANCE OF STARS.
We have been considering the planets so far as they are known to astronomers, but no doubt we shall find out others some day beyond Neptune in space, for it must be assumed that there are other planets wandering about in the infinite firmament. At present, however, we cannot spare time for such speculation; we have got to peep at the stars and their groupings.
“What little bits of things the stars are,” a child said once in our hearing; and there were others present who were inclined to believe that the tiny light spots we could see looked small—not because they were distant, but because they were of no great magnitude; and when those children were told that the tiny stars were “suns” like our sun, giving heat and light millions and millions of miles away,—and, so far as we can tell, some are much bigger and hotter than our own sun,—they were very much surprised indeed, and one little girl aptly quoted Dr. Watts:—
“Twinkle, twinkle, little star,
How I wonder what you are”!
Now let us endeavour to learn something about these apparently tiny specks, and why they “twinkle.”
At a very early period in the history of astronomy the observers of the heavens grouped stars together in fancied resemblances to men or animals; and these “constellations,” as they are termed, are combinations of fixed stars—that is, of stars which do not wander about as the planets do. But these so-called fixed stars have motions; they are only relatively fixed with reference to their positions to each other as they appear to revolve daily round the earth. But stars have a movement of their own, which is termed their “proper motion.”
It is to Halley that the discovery of these real star motions is due. He saw three very bright stars (Sirius, Aldebaran, and Arcturus) were not in the places they had been assigned. The sun also has been found to possess a “proper motion,” and, with the planets, is travelling as determined by Sir J. Herschel, to a particular place in the constellation called Hercules. There are now star catalogues and star maps, for the heavens have been as closely surveyed as the earth, and by accurate observations it has now become possible to find the position of every star usually visible. Some of the stars are used as “clock” stars, by which sidereal time can be calculated accurately, and the clocks thereby corrected. The stars, though termed “fixed,” are in perpetual movement—Arcturus at the rate of fifty miles a second, and others less. Only the rates of a few are known.
The number of the stars is beyond our calculation, and even the number of stars only visible in the telescope amount to millions, and these are called telescopic stars. The visible stars amount to about six thousand, and of course these are the brightest up to the sixth magnitude. There are more visible in the southern than in the northern hemisphere. The magnitudes of the stars range in classes according to the brightness of the stars observed, for this is really the test from the first magnitude to the sixth; after that the telescopic stars are seen up to the fifteenth or sixteenth. We can only see about three thousand stars at any one time from any place, although, as remarked above, many millions may be observed with a good telescope, and as many more, probably twenty millions, are invisible.