Part 1

Chapter 13,087 wordsPublic domain

THE NEW ASTRONOMY

SAMUEL PIERPONT LANGLEY, PH.D., LL.D.

DIRECTOR OF THE ALLEGHENY OBSERVATORY, MEMBER NATIONAL ACADEMY, FELLOW ROYAL ASTRONOMICAL SOCIETY, ETC., ETC.

Illustrated

BOSTON. TICKNOR AND COMPANY 211 Tremont Street 1888

_All rights reserved._

University Press: JOHN WILSON AND SON, CAMBRIDGE.

PREFACE.

I have written these pages, not for the professional reader, but with the hope of reaching a part of that educated public on whose support he is so often dependent for the means of extending the boundaries of knowledge.

It is not generally understood that among us not only the support of the Government, but with scarcely an exception every new private benefaction, is devoted to “the Old” Astronomy, which is relatively munificently endowed already; while that which I have here called “the New,” so fruitful in results of interest and importance, struggles almost unaided.

We are all glad to know that Urania, who was in the beginning but a poor Chaldean shepherdess, has long since become well-to-do, and dwells now in state. It is far less known than it should be that she has a younger sister now among us, bearing every mark of her celestial birth, but all unendowed and portionless. It is for the reader’s interest in the latter that this book is a plea.

CONTENTS.

CHAPTER PAGE

I. SPOTS ON THE SUN 1

II. THE SUN’S SURROUNDINGS 35

III. THE SUN’S ENERGY 70

IV. THE SUN’S ENERGY (_Continued_) 91

V. THE PLANETS AND THE MOON 117

VI. METEORS 175

VII. COMETS 199

VIII. THE STARS 221

INDEX 253

LIST OF ILLUSTRATIONS.

FIGURE PAGE

1. THE SUN’S SURROUNDINGS 4

2. VIEW OF THE SUN ON SEPT. 20, 1870 6

3. THE SUN ON SEPT. 22, 1870 6

4. THE SUN ON SEPT. 26, 1870 7

5. THE SUN ON SEPT. 19, 1870 8

6. THE SUN ON SEPT. 20, 1870 8

7. THE SUN ON SEPT. 21, 1870 9

8. THE SUN ON SEPT. 22, 1870 9

9. THE SUN ON SEPT. 23, 1870 10

10. THE SUN ON SEPT. 26, 1870 10

11. NASMYTH’S WILLOW LEAVES 11

12. THE CACTUS TYPE 12

13. EQUATORIAL TELESCOPE AND PROJECTION 13

14. POLARIZING EYE-PIECE 14

15. SPOT OF SEPT. 21, 1870 15

16. SPOT OF MARCH 5, 1873 15

17. SUN ON MARCH 5, 1873 18

18. “THE PLUME” SPOT OF MARCH 5 AND 6, 1873 19

19. TYPICAL SUN-SPOT OF DECEMBER, 1873 21

20. FROST CRYSTAL 23

21. CYCLONE SPOT 24

22. SPOT OF MARCH 31, 1875 25

23. CIRROUS CLOUD 27

24. SPOT OF MARCH 31, 1875 28

25. TYPICAL ILLUSTRATION OF FAYE’S THEORY 29

26. SPOT OF OCT. 13, 1876 30

27. PHOTOGRAPH OF EDGE OF SUN 31

28. FACULA 33

29. LUNAR CONE SHADOW 36

30. TRACK OF LUNAR SHADOW 39

31. INNER CORONA ECLIPSE OF 1869 40

32. SKETCH OF OUTER CORONA, 1869 41

33. TACCHINI’S DRAWING OF CORONA OF 1870 43

34. WATSON’S NAKED-EYE DRAWING OF CORONA OF 1870 44

35. PHOTOGRAPH SHOWING COMMENCEMENT OF OUTER CORONA 45

36. ECLIPSE OF 1857, DRAWING BY LIAIS 48

37. ENLARGEMENT OF PART OF FIG. 38 49

38. FAC-SIMILE OF PHOTOGRAPH OF CORONA OF 1871 51

39. “SPECTRES” 54

40. OUTER CORONA OF 1878 57

41. SPECTROSCOPE SLIT AND SOLAR IMAGE 59

42. SLIT AND PROMINENCES 59

43. TACCHINI’S CHROMOSPHERIC CLOUDS 62

44. TACCHINI’S CHROMOSPHERIC CLOUDS 62

45. VOGEL’S CHROMOSPHERIC FORMS 64

46. TACCHINI’S CHROMOSPHERIC FORMS 66

47. ERUPTIVE PROMINENCES 67

48. SUN-SPOTS AND PRICE OF GRAIN 77

49. SUN-SPOT OF NOV. 16, 1882, AND EARTH 80

50. GREENWICH RECORD OF DISTURBANCE OF MAGNETIC NEEDLE, NOV. 16 AND 17, 1882 81

51. SUN-SPOTS AND MAGNETIC VARIATIONS 87

52. GREENWICH MAGNETIC OBSERVATIONS, AUG. 3 AND 5, 1872 89

53. ONE CUBIC CENTIMETRE 93

54. POUILLET’S PYRHELIOMETER 93

55. BERNIÈRES’S GREAT BURNING-GLASS 103

56. A “POUR” FROM THE BESSEMER CONVERTER 105

57. PHOTOMETER-BOX 108

58. MOUCHOT’S SOLAR ENGINE 109

59. ERICSSON’S NEW SOLAR ENGINE, NOW IN PRACTICAL USE IN NEW YORK 113

60. SATURN 119

61. THE EQUATORIAL TELESCOPE AT WASHINGTON 122

62. JUPITER, MOON, AND SHADOW 125

63. THREE VIEWS OF MARS 129

64. MAP OF MARS 129

65. THE MOON 137

66. THE FULL MOON 141

67. GLASS GLOBE, CRACKED 145

68. PLATO AND THE LUNAR ALPS 149

69. THE LUNAR APENNINES: ARCHIMEDES 153

70. VESUVIUS AND NEIGHBORHOOD OF NAPLES 157

71. PTOLEMY AND ARZACHEL 161

72. MERCATOR AND CAMPANUS 165

73. WITHERED HAND 168

74. IDEAL LUNAR LANDSCAPE AND EARTH-SHINE 169

75. WITHERED APPLE 171

76. GASSENDI. NOV. 7, 1867 173

77. THE CAMP AT MOUNT WHITNEY 177

78. VESUVIUS DURING AN ERUPTION 183

79. METEORS OBSERVED NOV. 13 AND 14, 1868, BETWEEN MIDNIGHT AND FIVE O’CLOCK, A. M. 189

80. COMET OF DONATI, SEPT. 16, 1858 201

81. “A PART OF A COMET” 203

82. COMET OF DONATI, SEPT. 24, 1858 205

83. COMET OF DONATI, OCT. 3, 1858 209

84. COMET OF DONATI, OCT. 9, 1858 213

85. COMET OF DONATI, OCT. 5, 1858 217

86. TYPES OF STELLAR SPECTRA 222

87. THE MILKY WAY 225

88. SPECTRA OF STARS IN PLEIADES 231

89. SPECTRUM OF ALDEBARAN 235

90. SPECTRUM OF VEGA 235

91. GREAT NEBULA IN ORION 239

92. A FALLING MAN 243

93. A FLASH OF LIGHTNING 245

THE NEW ASTRONOMY.

SPOTS ON THE SUN.

The visitor to Salisbury Plain sees around him a lonely waste, utterly barren except for a few recently planted trees, and otherwise as desolate as it could have been when Hengist and Horsa landed in Britain; for its monotony is still unbroken except by the funeral mounds of ancient chiefs, which dot it to its horizon, and contrast strangely with the crowded life and fertile soil which everywhere surround its borders. In the midst of this loneliness rise the rude, enormous monoliths of Stonehenge,--circles of gray stones, which seem as old as time, and were there, as we now are told, the temple of a people which had already passed away, and whose worship was forgotten, when our Saxon forefathers first saw the place.

In the centre of the inner circle is a stone which is believed once to have been the altar; while beyond the outmost ring, quite away to the northeast upon the open plain, still stands a solitary stone, set up there evidently with some special object by the same unknown builders. Seen under ordinary circumstances, it is difficult to divine its connection with the others; but we are told that once in each year, upon the morning of the longest day, the level shadow of this distant, isolated stone is projected at sunrise to the very centre of the ancient sanctuary, and falls just upon the altar. The primitive man who devised this was both astronomer and priest, for he not only adored the risen god whose first beams brought him light and warmth, but he could mark its place, and though utterly ignorant of its nature, had evidently learned enough of its motions to embody his simple astronomical knowledge in a record so exact and so enduring that though his very memory has gone, common men are still interested in it; for, as I learned when viewing the scene, people are accustomed to come from all the surrounding country, and pass in this desolate spot the short night preceding the longest day of the year, to see the shadow touch the altar at the moment of sunrise.

Most great national observatories, like Greenwich or Washington, are the perfected development of that kind of astronomy of which the builders of Stonehenge represent the infancy. Those primitive men could know where the sun would rise on a certain day, and make their observation of its place, as we see, very well, without knowing anything of its physical nature. At Greenwich the moon has been observed with scarcely an intermission for one hundred and fifty years, but we should mistake greatly did we suppose that it was for the purpose of seeing what it was made of, or of making discoveries in it. This immense mass of Greenwich observations is for quite another purpose,--for the very practical purpose of forming the lunar tables, which, by means of the moon’s place among the stars, will tell the navigator in distant oceans where he is, and conduct the fleets of England safely home.

In the observatory at Washington one may see a wonderfully exact instrument, in which circles of brass have replaced circles of stone, all so bolted between massive piers that the sun can be observed by it but once daily, as it crosses the meridian. This instrument is the completed attainment along that long line of progress in one direction, of which the solitary stone at Stonehenge marks the initial step,--the attainment, that is, purely of precision of measurement; for the astronomer of to-day can still use his circles for the special purpose of fixing the sun’s place in the heavens, without any more knowledge of that body’s chemical constitution than had the man who built Stonehenge.

Yet the object of both is, in fact, the same. It is true that the functions of astronomer and priest have become divided in the advance of our modern civilization, which has committed the special cultivation of the religious aspect of these problems to a distinct profession; while the modern observer has possibly exchanged the emotions of awe and wonder for a more exact knowledge of the equinox than was possessed by his primitive brother, who both observed and adored. Still, both aim at the common end, not of learning what the sun is made of, but of where it will be at a certain moment; for the prime object of astronomy, until very lately indeed, has still been to say _where_ any heavenly body is, and not _what_ it is. It is this precision of measurement, then, which has always--and justly--been a paramount object of this oldest of the sciences, not only as a good in itself, but as leading to great ends; and it is this which the poet of Urania has chosen rightly to note as its characteristic, when he says,--

“That little Vernier, on whose slender lines The midnight taper trembles as it shines, Tells through the mist where dazzled Mercury burns, And marks the point where Uranus returns.”

But within a comparatively few years a new branch of astronomy has arisen, which studies sun, moon, and stars for what they are in themselves, and in relation to ourselves. Its study of the sun, beginning with its external features (and full of novelty and interest, even, as regards those), led to the further inquiry as to what it was made of, and then to finding the unexpected relations which it bore to the earth and our own daily lives on it, the conclusion being that, in a physical sense, it made us and re-creates us, as it were, daily, and that the knowledge of the intimate ties which unite man with it brings results of the most practical and important kind, which a generation ago were unguessed at.

This new branch of inquiry is sometimes called Celestial Physics, sometimes Solar Physics, and is sometimes more rarely referred to as the New Astronomy. I will call it here by this title, and try to tell the reader something about it which may interest him, beginning with the sun.

The whole of what we have to say about the sun and stars presupposes a knowledge of their size and distance, and we may take it for granted that the reader has at some time or another heard such statements as that the moon’s distance is two hundred and forty thousand miles, and the sun’s ninety-three million (and very probably has forgotten them again as of no practical concern). He will not be offered here the kind of statistics which he would expect in a college text-book; but we must linger a moment on the threshold of our subject--the nature of these bodies--to insist on the real meaning of such figures as those just quoted. We are accustomed to look on the sun and moon as far off together in the sky; and though we know the sun is greater, we are apt to think of them vaguely as things of a common order of largeness, away among the stars. It would be safe to say that though nine out of ten readers have learned that the sun is larger than the moon, and, in fact, larger than the earth itself, most of them do not at all realize that the difference is so enormous that if we could hollow out the sun’s globe and place the earth in the centre, there would still be so much room that the moon might go on moving in her present orbit at two hundred and forty thousand miles from the earth,--_all within the globe of the sun itself_,--and have plenty of room to spare.

As to the distance of ninety-three million miles, a cannon-ball would travel it in about fifteen years. It may help us to remember that at the speed attained by the Limited Express on our railroads a train which had left the sun for the earth when the “Mayflower” sailed from Delftshaven with the Pilgrim Fathers, and which ran at that rate day and night, would in 1887 still be a journey of some years away from its terrestrial station. The fare at the customary rates, it may be remarked, would be rather over two million five hundred thousand dollars, so that it is clear that we should need both money and leisure for the journey.

Perhaps the most striking illustration of the sun’s distance is given by expressing it in terms of what the physiologists would call velocity of nerve transmission. It has been found that sensation is not absolutely instantaneous, but that it occupies a very minute time in travelling along the nerves; so that if a child puts its finger into the candle, there is a certain almost inconceivably small space of time, say the one-hundredth of a second, before he feels the heat. In case, then, a child’s arm were long enough to touch the sun, it can be calculated from this known rate of transmission that the infant would have to live to be a man of over a hundred before it knew that its fingers were burned.

Trying with the help of these still inadequate images, we may get some idea of the real size and distance of the sun. I could wish not to have to dwell upon such figures, that seem, however, indispensable; but we are now done with these, and are ready to turn to the telescope and see what the sun itself looks like.

The sun, as we shall learn later, is a star, and not a particularly large star. It is, as has been said, “only a private in the host of heaven,” but it is one of that host; it is one of those glittering points to which we have been brought near. Let us keep in mind, then, from the first, what we shall see confirmed later, that there is an essentially similar constitution in them all, and not forget that when we study the sun, as we now begin to do, we are studying the stars also.

If we were called on to give a description of the earth and all that is on it, it would be easily understood that the task was impossibly great, and that even an account of its most striking general features might fill volumes. So it is with the sun; and we shall find that in the description of the general character of its immediate surface alone, there is a great deal to be told. First, let us look at a little conventional representation (Fig. 1), as at a kind of outline of the unknown regions we are about to explore. The circle represents the Photosphere, which is simply what the word implies, that “sphere” of “light” which we have daily before our eyes, or which we can study with the telescope. Outside this there is a thin envelope, which rises here and there into irregular prominences, some orange-scarlet, some rose-pink. This is the Chromosphere, a thin shell, mainly of crimson and scarlet tints, invisible even to the telescope except at the time of a total eclipse, when alone its true colors are discernible, but seen as to its form at all times by the spectroscope. It is always there, not hidden in any way, and yet not seen, only because it is overpowered by the intenser brilliancy of the Photosphere, as a glow-worm’s shine would be if it were put beside an electric light. Outside all is the strange shape, which represents the mysterious Corona, seen by the naked eye in a total eclipse, but at all other times invisible even to telescope and spectroscope, and of whose true nature we are nearly ignorant from lack of opportunity to study it.

Disregarding other details, let us carry in our minds the three main divisions,--the Photosphere, or daily visible surface of the sun, which contains nearly all its mass or substance; the Chromosphere; and the unsubstantial Corona, which is nevertheless larger than all the rest. We begin our examination with the Photosphere.

There are records of spots having been seen with the naked eye before the invention of the telescope, but they were supposed to be planets passing between us and the surface; and the idea that the sun was pure fire, necessarily immaculate, was taught by the professors of the Aristotelian philosophy in mediæval schools, and regarded almost as an article of religious faith. We can hardly conceive, now, the shock of the first announcement that spots were to be found on the sun, but the notion partook in contemporary minds at once of the absurd and the impious; and we notice here, what we shall have occasion to notice again, that these physical discoveries from the first affect men’s thoughts in unexpected ways, and modify their scheme of the moral universe as well as of the physical one.

Very little indeed was added to the early observations of Fabricius and Galileo until a time within the remembrance of many of us; for it is since the advent of the generation now on the stage that nine-tenths of the knowledge of the subject has been reached.