Читать книгу The Friendly Stars - Martha Evans Martin - Страница 10
ОглавлениеARCTURUS
Early in the evening in March another bright star may be seen rising a little north of east, which is among the choicest of the heavenly bodies. This is Arcturus. To find it begin at the end of the handle of the Big Dipper and, following the curve of the handle, extend a line about thirty degrees, or until you come to the first brilliantly shining star. There is no other very bright star in this region; so the line cannot point you to any other than Arcturus, the self-same star whose bright beams flowed down more than twenty-six hundred years ago upon the patient Job and is named by him along with other wonders of the divine creation.
When one has learned to know the ways of Arcturus and cares to greet him as he first comes to take his place among the evening stars in the spring, one begins about ten o'clock in the evening in February to watch the handle of the Dipper, so clearly, to the expectant observer, pointing to something important just below the horizon and then slowly rising until it has pulled into view the steady shining face of Arcturus. A less attentive observer is more likely to notice the star in March and April, when the Dipper is almost directly overhead and is turned as neatly upside down as if it were on the pantry shelf. Its handle, though, still points to Arcturus, now climbing the eastern skies composedly but rapidly, and making way for the other bright stars of the spring that will bring on the scene a stellar setting of their own.
Arcturus rises on the first of March about eight o'clock in the evening, and during this month, when the horse-chestnut buds are swelling and the elm-trees are putting forth their first brown blossoms, and the hawks and owls and crows are prospecting for nesting sites among the high trees, Arcturus, as if impelled by the onrush of spring, is returning four minutes earlier each evening until at the beginning of April the star rises just as the sun sets.
This is really the month of its greatest glory. It shines all through the evening in the eastern heavens, bright even when the moon is full, and, fitting in with all the other aspects of nature, gives a splendid close to the splendid days of late April. What more gracious day's progress in beauty could there be than to travel with the eye from the cheerful hepaticas dotting the soft ground among the trees to the round, white, silent blossoms of the dogwood fringing the late April woods and thence, when evening falls, to the bright yet gentle light of Arcturus in the sky, announcing the end of the purple twilight.
By the middle of June, Arcturus may be found during the early evening almost overhead, and it remains in this region during July. After this, one sees plainly that it is travelling towards the northwest, sinking lower and lower each month until, near the last of November, the pointing handle of the Dipper (the Dipper being then right-side up and below the pole) shows us that it has gone, almost at the same moment with the sun, below the northwestern horizon. It is in the evening skies no more until the next spring. If one wants to see Arcturus in December or January, he must look for it in the east between midnight and dawn. It shines for us at some time between sunset and midnight almost ten months in the year. It requires about fourteen and a half hours to complete its journey from rising to setting each day.
Arcturus and Capella are so nearly equal in brightness that astronomers differ as to which outranks the other, even when they measure their light with a supposedly accurate instrument and a trained eye. To my own eye Arcturus outshines Capella, and on asking various inexperienced persons for off-hand opinions as to the relative brightness of the two stars, I have invariably had an answer in favor of Arcturus. The best authorities, however, make Capella a shade brighter.
Arcturus, like Capella, is yellow in color and is known as a solar, or sun, type of star. It is, however, as one can plainly see, a little more tinged with red; and this indicates that it is perhaps a little farther along in its development from a gaseous to a solid body than either Capella or the sun, and that it is probably not quite so bright in proportion to its size.
Situated as we are, the sun gives to the earth billions of times as much light as Arcturus; but if the sun were as far away as Arcturus is, it would be one of the telescopic stars, entirely invisible to the naked eye. In actual light-giving power Arcturus exceeds the sun a thousand times. Its extreme distance is all that saves us from this tremendous light. It is so far away that with the unthinkable speed of light more than a hundred years must be required for it to come from Arcturus to us. If the star were blotted out of existence, the light that left it on the day of the catastrophe would, a hundred years later, still be travelling towards us and we should probably still be in ignorance of the fate of the star. Astronomers are fond of saying, and it is strictly true, that we see the stars only as they have been and never as they are.
Arcturus ranks with Canopus as one of the largest bodies in the universe. The diameter of our own sun is more than 866,000 miles, yet the sun is small in comparison with Arcturus, whose diameter is supposed to be several millions of miles. It is said also to be probably the hottest star in the universe; but this perhaps may prove to be a too precipitate statement. Actual results from experimental measurements of the heat of stars are very few, though Arcturus has been shown to give out more heat than Vega, another star with which it has been directly compared.
These facts are, perhaps, not what we most want to have in mind when we gaze into the face of Arcturus with its clear, steady light, but they must have their part in the sum of its general characteristics and some influence in determining our feeling towards the star.
Arcturus has the distinction of having the most rapid motion of any of the brightest stars and it is among the swiftest moving of all the stars visible to the naked eye. Enormous body as it is, we know that it is bowling along through space at the rate of between two and three hundred miles a second. It has been doing this for untold centuries, and yet it does not change its position to our view a distance of more than one-eighth of the apparent diameter of the moon in a century. This is, however, an enormous change for a "fixed" star and will, in the course of ages, make an important difference in the position of Arcturus among the other stars.
It is pleasant to know that this bright star is approaching us, though it lessens the distance between itself and us only at the rate of about five miles a second, a very loitering gait in comparison with the speed of stars in general. The most that it can mean to us is that Arcturus will not grow less bright in our skies, for at this rate of approach untold centuries must pass before the distance between us and the star is lessened so as to make any appreciable increase in its brightness. Such increase, indeed, possibly never will be made; for Arcturus is growing old, and it may be that its lustre will diminish as its distance decreases.
Arcturus lies in the constellation Boötes and is, of course, its brightest star.
