A Short History of Astronomy - Arthur Berry (read along books .txt) 📗
- Author: Arthur Berry
- Performer: -
Book online «A Short History of Astronomy - Arthur Berry (read along books .txt) 📗». Author Arthur Berry
1 In our climate 2,000 is about the greatest number ever visible at once, even to a keen-sighted person.
2 Owing to the greater brightness of the stars overhead they usually seem a little nearer than those near the horizon, and consequently the visible portion of the celestial sphere appears to be rather less than a half of a complete sphere. This is, however, of no importance, and will for the future be ignored.
3 A right angle is divided into ninety degrees (90°), a degree into sixty minutes (60′), and a minute into sixty seconds (60″).
4 I have made no attempt either here or elsewhere to describe the constellations and their positions, as I believe such verbal descriptions to be almost useless. For a beginner who wishes to become familiar with them the best plan is to get some better informed, friend to point out a few of the more conspicuous ones, in different parts of the sky. Others can then be readily added by means of a star-atlas, or of the star-maps given in many textbooks.
5 The names, in the customary Latin forms, are: Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpio, Sagittarius, Capricornus, Aquarius, and Pisces; they are easily remembered by the doggerel verses:—
6 This statement leaves out of account small motions nearly or quite invisible to the naked eye, some of which are among the most interesting discoveries of telescopic astronomy; see, for example, chapter X., §§ 207-215.
7 The custom of calling the sun and moon planets has now died out, and the modern usage will be adopted henceforward in this book.
8 It may be noted that our word “day” (and the corresponding word in other languages) is commonly used in two senses, either for the time between sunrise and sunset (day as distinguished from night), or for the whole period of 24 hours or day-and-night. The Greeks, however, used for the latter a special word, νυχθήμερον.
9 Compare the French: Mardi, Mercredi, Jeudi, Vendredi; or better still the Italian: Martedi, Mercoledi, Giovedi, Venerdi.
10 See, for example, Old Moore’s or Zadkiel’s Almanack.
11 We have little definite knowledge of his life. He was born in the earlier part of the 6th century B.C., and died at the end of the same century or beginning of the next.
12 Theophrastus was born about half a century, Plutarch nearly five centuries, later than Plato.
13 Republic, VII. 529, 530.
14 Confused, because the mechanical knowledge of the time was quite unequal to giving any explanation of the way in which these spheres acted on one another.
15 I have introduced here the familiar explanation of the phases of the moon, and the argument based on it for the spherical shape of the
Comments (0)