Читать книгу The Friendly Stars - Martha Evans Martin - Страница 11
ОглавлениеSPICA
Another bright star, and one that comes into view not long after Arcturus, is Spica. It is not so bright as Arcturus, but is still a conspicuously brilliant star. Among the twenty brightest it is the fifteenth in order of brilliancy. It can be found by extending the line from the end of the handle of the Dipper through Arcturus and about thirty degrees beyond, still following the curve. It is about as far from Arcturus as Arcturus is from the handle of the Dipper. A straight line beginning at the pointer nearest the pole, running through the star at the bottom of the Dipper on the handle side, and extended about sixty-five degrees farther on, will also point out Spica.
Spica rises a very little south of the exact eastern point on the horizon and becomes visible about an hour later than Arcturus. It is the only very bright star in the southeastern part of the heavens during the early spring months, and one cannot easily fail to identify it even without the specific directions for finding it that are here given. It first attracts one's attention in the early evening about the middle of March, at which time it rises about eight o'clock and by nine has cleared its face of the haziness of the lower atmosphere and is shining with a clear white light.
Spica does not make so long a sweep across the heavens as Capella and Arcturus do. It is one of the stars that lie a little south of the celestial equator, and at the highest point in its journey across the sky it is still to the south of us and almost one-half of the way up from the horizon to the point exactly overhead, which we call the zenith. It takes five hours and a half to reach its highest point and as many more to travel to the southwestern horizon, where it sets eleven hours after it has risen.
Spica rises just after the sun sets in the early part of April; and during April and May it is at its best in the eastern evening sky. Its position, however, keeping it always comparatively low in the sky to our view, makes it easy to observe at all times when it is visible. During the short evenings in June it is seen bearing off towards the southwest, where in August it sets about ten o'clock, in September at about eight o'clock, and in October about the same time that the sun goes down. It can be seen between sunset and midnight in some part of the sky from the middle of February to the early part of October. In November, December, and January it rises between midnight and dawn, so that October is the only month during which it is most of the time invisible. This is because it lies in the constellation Virgo, or the Virgin, through which the sun is passing in October, and the star is lost in the rays of the sun. Spica lies almost on the ecliptic, which is the line that marks the annual path of the sun through the heavens.
Spica's color (white) shows it to be in an earlier stage of existence than the yellow stars; hence it is known to be a much more tenuous, or rarefied, body than either Capella or Arcturus. It is one of the stars so far away that we have never been able to measure its distance. Shining so brightly as it does at an immeasurable distance, it must be of immense size and perhaps thousands of times brighter than our sun. The spectroscope has revealed that it is probably a double star and that it is moving towards the earth at the rate of more than fourteen miles a second. Perhaps in ages to come it will be near enough to yield some clue to its distance.
The name Spica means an ear of wheat, and the star marks the spot in the constellation Virgo where the Virgin holds in her hand a spear of wheat.
