CHAPTER XV
CLUSTERS AND NEBULÆ
Even the most casual observer of the heavens cannot have failed to notice that in certain instances the stars are grouped so closely together as to form well-marked clusters. The most familiar example is the well-known group of the Pleiades, in the constellation Taurus, while quite close is the more scattered group of the Hyades. Another somewhat coarsely scattered group is that known as Coma Berenices, the Hair of Berenice, which lies beneath the handle of the Plough; and a fainter group is the cluster Præsepe, which lies in the inconspicuous constellation Cancer, between Gemini and Leo, appearing to the naked eye like a fairly bright, hazy patch, which the smallest telescope resolves into a cloud of faint stars.
The Pleiades form undoubtedly the most remarkable naked-eye group in the heavens. The six stars which are visible to average eyesight are Alcyone, 3rd magnitude; Maia, Electra, and Atlas, of the 4th; Merope, 4-1/3; and Taygeta, 4-1/2. While Celæno, 5-1/3; Pleione, 5-1/2; and Asterope, 6, hang on the verge of visibility. With an opera-glass about thirty more may be counted, while photographs show between 2,000 and 3,000. It is probable that the fainter stars have no real connection with the cluster itself, which is merely seen upon a background of more distant star-dust. Modern photographs have shown that this cluster is involved in a great nebula, which stretches in curious wisps and straight lines from star to star, and surrounds the whole group. The Pleiades make a brilliant object for a small telescope with a low magnifying power, but are too scattered for an instrument of any size to be effective upon them. The finest of all irregular star-clusters is that known as the Sword-handle of Perseus. Midway between Perseus and the W of Cassiopeia, and directly in the line of the Galaxy, the eye discerns a small, hazy patch of light, of which even a 2 or 3 inch glass will make a beautiful object, while with a large aperture its splendour is extraordinary. It consists of two groups of stars which are both in the same field with a small instrument and low powers. Towards the edge of the field the stars are comparatively sparsely scattered; but towards the two centres of condensation the thickness of grouping steadily increases. Altogether there is no more impressive stellar object than this magnificent double cluster (Plate XXVIII., 2). Another very fine example of the irregular type of grouping is seen in M. 35, situated in the constellation Gemini, and forming an obtuse-angled triangle with the stars Mu and Eta Geminorum (Plate XXVIII., 1). There are many other similar groups fairly well within the reach of comparatively small instruments, and some of these are mentioned in the list of objects (Appendix II.).
Still more remarkable than the irregular clusters are those which condense into a more or less globular form. There are not very many objects of this class in the northern sky visible with a small telescope, but the beauty of those which are visible is very notable. The most splendid of all is the famous cluster M. 13 Herculis. (The M. in these cases refers to the catalogue of such objects drawn up by Messier, the French 'comet ferret,' to guide him in his labours.) M. 13 is situated almost on the line between Zeta and Eta Herculis, and at about two-thirds of the distance from Zeta towards Eta. It is faintly visible to the unaided eye when its place is known, and, when viewed with sufficient telescopic power, is a very fine object. Nichol's remark that 'perhaps no one ever saw it for the first time through a large telescope without uttering a shout of wonder' seems to be based on a somewhat extravagant estimate of the enthusiasm and demonstrativeness of the average star-gazer; but the cluster is a very noble object all the same, consisting, according to a count made on a negative taken in 1899, of no fewer than 5,482 stars, which condense towards the centre into a mass of great brilliancy. It takes a large aperture to resolve the centre of the cluster into stars, but even a 3-inch will show a number of twinkling points of light in the outlying streamers (Plate XXIX.). In the same constellation will also be found the cluster M. 92, similar to, but somewhat fainter than M. 13; and other globular clusters are noted in the Appendix. Most of these objects, however, can only be seen after a fashion with small instruments. Of the true nature and condition of these wonderful aggregations we are so far profoundly ignorant. The question of whether they are composed of small stars, situated at no very great distance from the earth, or of large bodies, which are rendered faint to our vision by immense distance, has been frequently discussed. Gore concludes that they are 'composed of stars of average size and mass, and that the faintness of the component stars is simply due to their immense distance from the earth.' If so, the true proportions of some of these clusters must be indeed phenomenal! A very remarkable feature to be noticed in connection with some of them is the high proportion of variable stars which they contain. Professor Bailey has found that in such clusters as M. 3 and M. 5 the proportion of variables is one in seven and one in eleven respectively, while several other groups show proportions ranging from one in eighteen up to one in sixty. As the general proportion of variables is somewhere about one in a hundred, these ratios are remarkable. They only characterize a certain number of clusters, however, and are absent in cases which seem strictly parallel to others where they exist.
We now pass from the star-clusters to the nebulæ properly so called. Till after the middle of last century it was an open question whether there was any real distinction between the two classes of bodies. Herschel had suggested the existence of a 'shining fluid,' distributed through space, whose condensations gave rise to those objects known as nebulæ; but it was freely maintained by many that the objects which could not be resolved into stars were irresolvable only because of their vast distance, and that the increase of telescopic power would result in the disclosure of their stellar nature. This view seemed to be confirmed when it was confidently announced that the great Rosse telescope had effected the resolution of the Orion Nebula, which was looked upon as being in some sort a test case. But the supposed proof of the stellar character of nebulæ did not hold its ground for long, for in 1864 Sir William Huggins, on applying the spectroscope to the planetary nebula in Draco, found that its spectrum consisted merely of bright lines, one of which--the most conspicuous--was close to the position of a nitrogen line, but has proved to be distinct from it; while of the other two, one was unmistakably the F line of hydrogen and the other remains still unidentified. Thus it became immediately manifest that the nebula in Draco did not consist of distant stars, but was of gaseous constitution; and Sir William Herschel's idea of the existence of non-stellar matter in the universe was abundantly justified. Subsequent research has proved that multitudes of nebulæ yield a bright-line spectrum, and are therefore gaseous. Of these, by far the most remarkable and interesting is the Great Nebula of Orion. The observer will readily distinguish even with the unaided eye that the middle star of the three that form the sword which hangs down from Orion's belt has a somewhat hazy appearance. A small telescope reveals the fact that the haziness is due to the presence of a great misty cloud of light, in shape something like a fish-mouth, and of a greenish colour. At the junction of the jaws lies the multiple star Theta Orionis, which with a 2- or 3-inch glass appears to consist of four stars--'the trapezium'--large instruments showing in addition two very faint stars.
With greater telescopic power additional features begin to reveal themselves; the mist immediately above the trapezium assumes a roughly triangular shape, and is evidently much denser than the rest of the nebula, presenting a curdled appearance similar to that of the stretches of small cloud in a 'mackerel' sky; while from the upper jaw of the fish-mouth a great shadowy horn rises and stretches upward, until it gradually loses itself in the darkness of the background. This wonderful nebula appears to have been discovered in 1618, but was first really described and sketched by Huygens in 1656, since when it has been kept under the closest scrutiny, innumerable drawings of it having been made and compared from time to time with the view of detecting any traces of change. The finest drawings extant are those of Sir John Herschel and Mr. Lassell, and the elaborate one made with the help of the Rosse 6-foot mirror.
Drawing, however, at no time a satisfactory method of representing the shadowy and elusive forms of nebulæ, has now been entirely superseded by the work of the sensitive plate. Common, Roberts, Pickering, and others have succeeded admirably in photographing the Great Nebula with exposures ranging from half an hour up to six hours. The extension of nebulous matter revealed by these photographs is enormous (Plate XXX.), so much so that many of the central features of the nebula with which the eye is familiar are quite masked and overpowered in the photographic print. The spectrum of the Orion Nebula exhibits indications of the presence of hydrogen and helium, as well as the characteristic green ray which marks the unknown substance named 'nebulium.'
The appearance of this 'tumultuous cloud, instinct with fire and nitre,' is always amazing. Sir Robert Ball considers it one of the three most remarkable objects visible in the northern heavens, the other two being Saturn and the Great Cluster in Hercules. But, beautiful and wonderful as both of these may be, the Orion Nebula conveys to the mind a sense of mystery which the others, in spite of their extraordinary features, never suggest. Absolutely staggering is the thought of the stupendous dimensions of the nebula. Professor Pickering considers its parallax to be so small as to indicate a distance of not less than 1,000 years light journey from our earth! It is almost impossible to realize the meaning of such a statement. When we look at this shining mist, we are seeing it, not as it is now, but as it was more than a hundred years before the Norman Conquest; were it blotted out of existence now, it would still shine to us and our descendants for another ten centuries in virtue of the rays of light which are already speeding across the vast gulf that separates our world from its curdled clouds of fire-mist, and the astronomers of A.D. 2906 might still be speculating on the nature and destiny of a thing which for ages had been non-existent! That an object should be visible at all at such a distance demands dimensions which are really incomprehensible; but the Orion Nebula is not only visible, it is conspicuous!
The rival of this famous nebula in point of visibility is the well-known spiral in the girdle of Andromeda. On a clear night it can easily be seen with the naked eye near the star Nu Andromedæ, and may readily be, as it has often been, mistaken for a comet. Its discovery must, therefore, have been practically coincident with the beginnings of human observation of the heavens; but special mention of it does not occur before the tenth century of our era. A small telescope will show it fairly well, but it must be admitted that the first view is apt to produce a feeling of disappointment. The observer need not look for anything like the whirling streams of light which are revealed on modern long exposure photographs (Plate XXXI., 1). He will see what Simon Marius so aptly described under the simile of 'the light seen from a great distance through half-transparent horn plates'--a lens-shaped misty light, brightening very rapidly towards a nucleus which seems always on the point of coming to definition but is never defined, and again fading away without traceable boundary into obscurity on every side. The first step towards an explanation of the structure of this curious object was made by Bond in the middle of last century. With the 15-inch refractor of the Cambridge (U.S.A.) Observatory, he detected two dark rifts running lengthwise through the bright matter of the nebula; but it was not till 1887 and 1888 that its true form was revealed by Roberts's photographs. It was then seen to be a gigantic spiral or whirlpool, the rifts noticed by Bond being the lines of separation between the huge whorls of the spiral. Of course, small instruments are powerless to reveal anything of this wonderful structure; still there is an interest in being able to see, however imperfectly, an object which seems to present to our eyes the embodiment of that process by which some assume that our own system may have been shaped. So far as the powers of the best telescopes go, the Andromeda Nebula presents no appearance of stellar constitution. Its spectrum, according to Scheiner, is continuous, which would imply that in spite of appearances it is in reality composed of stars; but Sir William Huggins has seen also bright lines in it. Possibly it may represent a stage intermediate between the stellar and the gaseous.
2. [North.]
Photographs of Spiral Nebulæ. By Dr. Max Wolf.
1. Great Nebula in Andromeda. 2. Spiral in Triangulum (M. 33). ]
Another remarkable example of a spiral nebula will be found in M. 51. It is situated in the constellation Canes Venatici, and may be easily picked up, being not far from the end star of the Plough-handle Eta Ursæ Majoris. This strange object, 'gyre on gyre' of fire-mist, was one of the first spirals to have its true character demonstrated by the Rosse telescope. It is visible with moderate optical powers, but displays to them none of that marvellous structure which the great 6-foot mirror revealed for the first time, and which has been amply confirmed by subsequent photographic evidence (Plate XXXII.).
Among other classes of nebulæ we can only mention the ring and the planetary. Of each of these, one good example can be seen, though, it must be admitted, not much more than seen, with very modest instrumental equipment. Midway between the two stars Beta and Gamma Lyræ, already referred to in connection with the variability of the former, the observer by a little fishing will find the famous Ring Nebula of Lyra. With low powers it appears simply as a hazy oval spot; but it bears magnifying moderately well, and its annular shape comes out fairly with a power of eighty on a 2-1/2 inch, though it can scarcely be called a brilliant object with that aperture, or indeed with anything much under 8 inches. None the less, it is of great interest, the curious symmetry of this gaseous ring making it an almost unique object. It resembles nothing so much as those vortex rings which an expert smoker will sometimes send quivering through the air. Photographs show clearly a star within the ring, and this star has a very curious history, having been frequently visible in comparatively small telescopes, and again, within a year or two, invisible in much larger ones. Photography seems to have succeeded in persuading it to forgo these caprices, though it presents peculiarities of light which are still unexplained. The actinic plate reveals also very clearly that deficiency of light at the ends of the longer diameter of the ring which can be detected, though with more difficulty, by the eye. The class of annular nebulæ is not a large one, and none of its other members come within the effective range of small instruments.
Planetary nebulæ are so called because with ordinary powers they present somewhat of the appearance of a planet seen very dimly and considerably out of focus. The appearance of uniformity in their boundaries vanishes under higher telescopic power, and they appear to be generally decidedly elliptical; they yield a gaseous spectrum with strong evidence of the presence of 'nebulium,' the unknown substance which gives evidence of its presence in the spectrum of every true nebula, and has, so far (with one doubtful exception) been found nowhere else. The chief example of the class is that body in Draco which first yielded to Huggins the secret of the gaseous nature of the nebulæ. It lies nearly half-way between Polaris and Gamma Draconis, and is described by Webb as a 'very luminous disc, much like a considerable star out of focus.' It is by no means a striking object, but has its own interest as the first witness to the true nature of that great class of heavenly bodies to which it belongs.
The multitude of nebulous bodies scattered over the heavens may be judged from the fact that Professor Keeler, after partial surveys carried out by means of photography with the Crossley reflector, came to the conclusion that the number within the reach of that instrument (36-inch aperture) might be put down at not less than 120,000. It is a curious fact that the grouping of this great multitude seems to be fundamentally different from that of the stars. Where stars are densely scattered, nebulæ are comparatively scarce; where nebulæ abound, the stars are less thickly sown. So much is this the case, that, when Herschel in his historic 'sweeps' of the heavens came across a notably starless region, he used to call out to his assistant to 'prepare for nebulæ.' The idea of a physical connection between the two classes of bodies is thus underlined in a manner which, as Herbert Spencer saw so early as 1854, is quite unmistakable.
There remain one or two questions of which the very shortest notice must suffice--not because they are unimportant, but because their importance is such that any attempt at adequate discussion of them is impossible in our limited space. One of these inevitably rises to the mind in presence of the myriads of the heavenly host--the familiar question which was so pleasingly suggested to our growing minds by the nursery rhyme of our childhood. To the question, What is a star? it has now become possible to give an answer which is satisfactory so far as it goes, though it is in a very rudimentary stage as regards details.
The spectroscope has taught us that the stars consist of incandescent solid bodies, or of masses of incandescent gas so large and dense as not to be transparent; and further, that they are surrounded by atmospheres consisting of gases cooler than themselves. The nature of the substances incandescent in the individual bodies has also to some extent been learned. The result has been to show that, while there is considerable variety in the chemical constitution and condition of the stars, at least five different types being recognised, each capable of more minute subdivision, the stars are, in the main, composed of elements similar to those existing in the sun; and, in Professor Newcomb's words, 'as the sun contains most of the elements found on the earth and few or no others, we may say that earth and stars seem to be all made out of like matter.' It is, of course, impossible to say what unknown elements may exist in the stars; but at least it is certain that many substances quite familiar to us, such as iron, magnesium, calcium, hydrogen, oxygen, and carbon, are present in their constitution. Indeed, our own sun, in spite of its overwhelming importance to ourselves is to be regarded, relatively to the stellar multitudes, as merely one star among many; nor, so far as can be judged, can it be considered by any means a star of the first class. There can be no doubt that, if removed to the average distance of first magnitude stars--thirty-three years light journey--our sun would be merely a common-place member of the heavenly host, far outshone by many of its fellow-suns. In all probability it would shine as about a fifth magnitude star, with suspicions of variability in its light.
There remains to be noted the fact that the sun is not to be regarded as a fixed centre, its fixity being only relative to the members of its own system. With all its planets and comets it is sweeping continually through space with a velocity of more than 1,000,000 miles in the twenty-four hours. This remarkable fact was first suspected by Sir William Herschel, who also, with that insight which was characteristic of his wonderful genius, saw, and was able roughly to apply, the method which would either confirm or disprove the suspicion.
The principle which lies at the bottom of the determination is in itself simple enough, though its application is complicated in such a manner as to render the investigation a very difficult one. A wayfarer passing up the centre of a street lighted on both sides by lamps will see that the lamps in front of him appear to open out and separate from one another as he advances, while those that he is leaving behind him have an opposite motion, appearing to close in upon one another. Now, with regard to the solar motion, if the case were absolutely simple, the same effect would be produced upon the stars among which we are moving; that is to say, were the stars absolutely fixed, and our system alone in motion among them, there would appear to be a general thinning out or retreating of the stars from the point towards which the sun is moving, and a corresponding crowding together of them towards the point, directly opposite in the heavens, from which it is receding. In actual fact the case is not by any means so simple, for the stars are not fixed; they have motions of their own, some of them enormously greater than the motion of the sun. Thus the apparent motion caused by the advance of our system is masked to a great extent by the real motion of the stars. It is plain, however, that the perspective effect of the sun's motion must really be contained in the total motion of each star, or, in other words, that each star, along with its own real motion, must have an apparent motion which is common to all, and results from our movement through space. If this common element can be disentangled from the individual element, the proper motion of each star, then the materials for the solution of the problem will be secured. It has been found possible to effect this disentanglement, and the results of all those who have attempted the problem are, all things considered, in remarkably close agreement.
Herschel's application of his principle led him to the conclusion that there was a tendency among the stars to widen out from the constellation Hercules, and to crowd together towards the opposite constellation of Argo Navis in the southern hemisphere, and the point which he fixed upon as the apex of the sun's path was near the star Lambda Herculis. Subsequent discussions of the problem have confirmed, to a great extent, his rough estimate, which was derived from a comparatively small number of stars. So far as general direction was concerned, he was entirely right; the conclusion which he reached as to the exact point towards which the motion is directed has, however, been slightly modified by the discussion of a much larger number of stars, and it is now considered that the apex of the solar journey 'is in the general direction of the constellation Lyra, and perhaps near the star Vega, the brightest of that constellation' (Newcomb, 'The Stars,' p. 91). There are but few stars more beautiful and interesting than Vega; to its own intrinsic interest must now be added that arising from the fact that each successive night we look upon it we have swept more than 1,000,000 miles nearer to its brilliant globe, and that with every year we have lessened, by some 400,000,000 miles, the distance that divides us from it. There can surely be no thought more amazing than this! It seems to gather up and bring to a focus all the other impressions of the vastness of celestial distances and periods. So swift and ceaseless a motion, and yet the gulfs that sever us from our neighbours in space are so huge that a millennium of such inconceivable travelling makes no perceptible change upon the face of the heavens! There rise other thoughts to the mind. Towards what goal may our world and its companions be voyaging under the sway of the mighty ruler of the system, and at the irresistible summons of those far-off orbs which distance reduces to the mere twinkling points of light that in man's earliest childlike thought were but lamps hung out by the Creator to brighten the midnight sky for his favourite children? What strange chances may be awaiting sun and planet alike in those depths of space towards which we are rushing with such frightful speed? Such questions remain unanswered and unanswerable. We are as ignorant of the end of our journey, and of the haps that may attend it, as we are helpless in the grasp of the forces that compel and control it.
APPENDIX I
The following is a list of the Lunar Formations numbered as on the Key-map, Plate XIX.:
1. Newton. | 38. Heinsius. | 75. Playfair. 2. Short. | 39. Hainzel. | 76. Azophi. 3. Simpelius. | 40. Bouvard. | 77. Sacrobosco. 4. Manzinus. | 41. Piazzi. | 78. Fracastorius. 5. Moretus. | 42. Ramsden. | 79. Santbech. 6. Gruemberger. | 43. Capuanus. | 80. Petavius. 7. Casatus. | 44. Cichus. | 81. Wilhelm Humboldt. 8. Klaproth. | 45. Wurzelbauer. | 82. Polybius. 9. Wilson. | 46. Gauricus. | 83. Geber. 10. Kircher. | 47. Hell. | 84. Arzachel. 11. Bettinus. | 48. Walter. | 85. Thebit. 12. Blancanus. | 49. Nonius. | 86. Bullialdus. 13. Clavius. | 50. Riccius. | 87. Hippalus. 14. Scheiner. | 51. Rheita. | 88. Cavendish. 15. Zuchius. | 52. Furnerius. | 89. Mersenius. 16. Segner. | 53. Stevinus. | 90. Gassendi. 17. Bacon. | 54. Hase. | 91. Lubiniezky. 18. Nearchus. | 55. Snellius. | 92. Alpetragius. 19. Vlacq. | 56. Borda. | 93. Airy. 20. Hommel. | 57. Neander. | 94. Almanon. 21. Licetus. | 58. Piccolomini. | 95. Catherina. 22. Maginus. | 59. Pontanus. | 96. Cyrillus. 23. Longomontanus. | 60. Poisson. | 97. Theophilus. 24. Schiller. | 61. Aliacensis. | 98. Colombo. 25. Phocylides. | 62. Werner. | 99. Vendelinus. 26. Wargentin. | 63. Pitatus. | 100. Langrenus. 27. Inghirami. | 64. Hesiodus. | 101. Goclenius. 28. Schickard. | 65. Mercator. | 102. Guttemberg. 29. Wilhelm I. | 66. Vitello. | 103. Isidorus. 30. Tycho. | 67. Fourier. | 104. Capella. 31. Saussure. | 68. Lagrange. | 105. Kant. 32. Stöfler. | 69. Vieta. | 106. Descartes. 33. Maurolycus. | 70. Doppelmayer. | 107. Abulfeda. 34. Barocius. | 71. Campanus. | 108. Parrot. 35. Fabricius. | 72. Kies. | 109. Albategnius. 36. Metius. | 73. Purbach. | 110. Alphonsus. 37. Fernelius. | 74. La Caille. | ----------------------+---------------------+------------------- 111. Ptolemæus. | 151. Agrippa. | 191. Archimedes. 112. Herschel. | 152. Arago. | 192. Timocharis. 113. Davy. | 153. Taruntius. | 193. Lambert. 114. Gueriké. | 154. Apollonius. | 194. Diophantus. 115. Parry. | 155. Schubert. | 195. Delisle. 116. Bonpland. | 156. Firmicus. | 196. Briggs. 117. Lalande. | 157. Silberschlag. | 197. Lichtenberg. 118. Réaumur. | 158. Hyginus. | 198. Theætetus. 119. Hipparchus. | 159. Ukert. | 199. Calippus. 120. Letronne. | 160. Boscovich. | 200. Cassini. 121. Billy. | 161. Ross. | 201. Gauss. 122. Fontana. | 162. Proclus. | 202. Messala. 123. Hansteen. | 163. Picard. | 203. Struve. 124. Damoiseau. | 164. Condorcet. | 204. Mason. 125. Grimaldi. | 165. Plinius. | 205. Plana. 126. Flamsteed. | 166. Menelaus. | 206. Burg. 127. Landsberg. | 167. Manilius. | 207. Baily. 128. Mösting. | 168. Eratosthenes. | 208. Eudoxus. 129. Delambre. | 169. Gay Lussac. | 209. Aristoteles. 130. Taylor. | 170. Tobias Mayer. | 210. Plato. 131. Messier. | 171. Marius. | 211. Pico. 132. Maskelyne. | 172. Olbers. | 212. Helicon. 133. Sabine. | 173. Vasco de Gama. | 213. Maupertuis. 134. Ritter. | 174. Seleucus. | 214. Condamine. 135. Godin. | 175. Herodotus. | 215. Bianchini. 136. Sömmering. | 176. Aristarchus. | 216. Sharp. 137. Schröter. | 177. La Hire. | 217. Mairan. 138. Gambart. | 178. Pytheas. | 218. Gérard. 139. Reinhold. | 179. Bessel. | 219. Repsold. 140. Encke. | 180. Vitruvius. | 220. Pythagoras. 141. Hevelius. | 181. Maraldi. | 221. Fontenelle. 142. Riccioli. | 182. Macrobius. | 222. Timæus. 143. Lohrmann. | 183. Cleomedes. | 223. Epigenes. 144. Cavalerius. | 184. Römer. | 224. Gärtner. 145. Reiner. | 185. Littrow. | 225. Thales. 146. Kepler. | 186. Posidonius. | 226. Strabo. 147. Copernicus. | 187. Geminus. | 227. Endymion. 148. Stadius. | 188. Linné. | 228. Atlas. 149. Pallas. | 189. Autolycus. | 229. Hercules. 150. Triesnecker. | 190. Aristillus. |
In the accompanying brief notes on a few important formations, the diameter of each is given in miles, and the height of the highest peak on wall in feet. The day of each lunation on which it may be well seen is also added.
NO.
22. MAGINUS.--Great walled plain; 100 miles; 14,000 feet. Central mountain 2,000 feet. Difficult in full, owing to rays from Tycho. Plate XIV. Eighth and ninth days.
23. LONGOMONTANUS.--Walled plain; 90 miles; 13,314 feet. Crossed by rays from Tycho. Plate XV. Ninth day.
26. WARGENTIN; 28. SCHICKARD.--Close together. 26. Curious ring plain; 54 miles. Seemingly filled with lava. 'Resembles a large thin cheese.' 28. Great walled plain; 134 miles; 9,000 feet. Floor 13,000 square miles area, very varied in colour. Walls would be invisible to spectator in centre of enclosure. Plate XII. Thirteenth and fourteenth days.
30. TYCHO.--Splendid ring plain; 54 miles; 17,000 feet. Central mountain 5,000 feet. Great system of streaks from neighbourhood. Plates XII., XIII., XV. Ninth and tenth days.
32. STÖFLER.--Walled plain. Peak on N.E. wall 12,000 feet. Floor very level. Beautiful steel-grey colour. Plate XVI. Seventh day.
33. MAUROLYCUS.--Walled plain; 150 miles; 14,000 feet. In area equal to about half of Ireland. Floor in full covered with bright streaks. Plate XVI. Seventh day.
58. PICCOLOMINI.--Ring plain; 57 miles; 15,000 feet on E. Fine central mountain. Very rugged neighbourhood. Plate XI. Fifth and sixth days.
63. PITATUS.--58 miles. Wall massive on S., but breached on N. side, facing Mare Nubium. Two clefts in interior shown Plate XV. Ninth day.
78. FRACASTORIUS.--Another partially destroyed formation; 60 miles. Wall breached on N., facing Mare Nectaris. Under low sun traces of wall can be seen. Plate XI. Fifth and sixth days.
80. PETAVIUS.--Fine object; 100 miles; 11,000 feet. Fine central peak 6,000 feet. Great cleft from central mountain to S.E. wall can be seen with 2-inch. Third and fourth days, but best seen on waning moon a day or two after full.
90. GASSENDI.--Walled plain; 55 miles. Wall on N. broken by intrusive ring-plain of Gassendi A. Fine central mountain 4,000 feet. Between thirty and forty clefts in floor, more or less difficult. Plates XII., XIII. Eleventh and twelfth days.
95. CATHERINA; 96. CYRILLUS; 97. THEOPHILUS.--Fine group of three great walled plains. 95. Very irregular; 70 miles; 16,000 feet. Connected by rough valley with 96. 96 has outline approaching a square; walls much terraced, overlapped by 97, and partially ruined on N.E. side. 97 is one of the finest objects on moon; 64 miles; terraced wall, 18,000 feet. Fine central mountain 6,000 feet. Plates XI., XVI. Sixth day.
84. ARZACHEL; 110. ALPHONSUS; 111. PTOLEMÆUS.--Another fine group. 84 is southernmost; 66 miles; 13,000 feet. Fine central mountain. 110. Walled plain; 83 miles; abutting on 111. Wall rises to 7,000 feet. Bright central peak. Three peculiar dark patches on floor, best seen towards full. 111 is largest of three; 115 miles. Many large saucer-shaped hollows on floor under low sun. Area 9,000 square miles. Plate XIII. Eighth and ninth days.
125. GRIMALDI.--Darkest walled plain on moon; 148 miles by 129; area 14,000 square miles; 9,000 feet. Plate XII. Thirteenth and fourteenth days.
131. MESSIER AND MESSIER A.--Two bright craters; 9 miles. Change suspected in relative sizes. From Messier A two straight light rays like comet's tail extend across Mare F[oe]cunditatis. Fourth and fifth days.
147. COPERNICUS.--Grand object; 56 miles; 10,000 to 12,000 feet. Central mountain 2,400 feet. Centre of system of bright rays. On W. a remarkable crater row; good test for definition. Plates XII., XIII. Ninth and tenth days.
150. TRIESNECKER.--Small ring plain; 14 miles. Terraced wall 5,000 feet. Remarkable cleft-system on W. Rather delicate for small telescopes. Plate XIII. Seventh and eighth days.
158. HYGINUS.--Crater-pit 3·7 miles. Remarkable cleft runs through it; visible with 2-inch: connected with Ariadæus rill to W., which also an object for a 2-inch. Dark spot to N.W. on Mare Vaporum named Hyginus N. Has been suspected to be new formation. Plate XII. Seventh day.
168. ERATOSTHENES.--Fine ring plain at end of Apennines; 38 miles. Terraced wall 16,000 feet above interior, which is 8,000 feet below Mare Imbrium. Fine central mountain. Plate XIII. Remarkable contrast to 148 Stadius, which has wall only 200 feet, with numbers of craters on floor. Ninth and tenth days.
175. HERODOTUS; 176. ARISTARCHUS.--Interesting pair. 175 is 23 miles; 4,000 feet. Floor very dusky. Great serpentine valley; most interesting object. Easy with 2-inch. 176 is most brilliant crater on moon; 28 miles; 6,000 feet. Central peak very bright. Readily seen on dark part of moon by earth-shine. Plates XII., XIII. Twelfth day.
188. LINNÉ.--Small crater on M. Serenitatis near N.W. end of Apennines. Suspected of change, but varies much in appearance under different lights. Visible on Plate XVII. as whitish oval patch to left of end of Apennines. Seventh day.
191. ARCHIMEDES.--Fifty miles; 7,000 feet. Floor very flat; crossed by alternate bright and dark zones. Makes with 189 and 190 fine group well shown Plate XVII. Eighth day.
208. EUDOXUS; 209. ARISTOTELES.--Beautiful pair of ring plains. 208 is 40 miles. Walls much terraced; 10,000 to 11,000 feet; 209 is 60 miles; 11,000 feet. Plate XVII. Sixth and seventh days.
210. PLATO.--Great walled plain; 60 miles; 7,400 feet. Dark grey floor, which exhibits curious changes of colour under different lights, also spots and streaks too difficult for small telescope. Landslip on E. side. Shadows very fine at sunrise. Plates XII., XIII. Ninth day.
211. PICO.--Isolated mountain; 7,000 to 8,000 feet. S. of 210. Casts fine shadow when near terminator. Ninth and tenth days.
228. ATLAS; 229. HERCULES.--Beautiful pair. 228 is 55 miles; 11,000 feet. Small but distinct central mountain. 229 is 46 miles. Wall reaches same height as 228, and is finely terraced. Landslip on N. wall. Conspicuous crater on floor. Plate XI. Fifth day.
APPENDIX II
The following list includes a number of double and multiple stars, clusters, and nebulæ, which may be fairly well seen with instruments up to 3 inches in aperture. A few objects have been added on account of their intrinsic interest, which may prove pretty severe tests. The places given are for 1900, and the position-angles and distances are mainly derived from Mr. Lewis's revision of Struve's 'Mensuræ Micrometricæ,' Royal Astronomical Society's Memoirs, vol. lvi., 1906. For finding the various objects, Proctor's larger Star Atlas, though constructed for 1880, is still, perhaps, the most generally useful. Cottam's 'Charts of the Constellations' (Epoch 1890) are capital, but somewhat expensive. A smaller set of charts will be found in Ball's 'Popular Guide to the Heavens,' while Peck has also published various useful charts. The student who wishes fuller information than that contained in the brief notes given below should turn to Gore's exceedingly handy volume, 'The Stellar Heavens.'
The brighter stars are generally known by the letters of the Greek alphabet, prefixed to them by Bayer. When these are used up, recourse is had either to the numbers in Flamsteed's Catalogue, or to those in Struve's 'Mensuræ Micrometricæ.' The Struve numbers are preceded by the Greek [Sigma]. A few of the more notable variable and red stars are included; these are generally marked by capital letters, as V. AQUILÆ. The order of the notes is as follows. First is given the star's designation, then its place in hours and minutes of right ascension and degrees and minutes of declination, N. and S. being marked respectively by + and -; then follow the magnitudes; the position-angles, which are measured in degrees from the north, or bottom point of the field, round by east, south, and west to north again; the distances of the components from one another in seconds of arc; and, finally, short notes as to colour, etc. According to Dawes, one inch aperture should separate the components of a 4·56″ double star, two inches those of a 2·28″, three those of a 1·52″, and so on. If the observer's glass can do this on good nights there is little fault to find with it. Double stars may be difficult for other reasons than the closeness of the components; thus, a faint companion to a bright star is more difficult to detect than a companion which is not far below its primary in brightness. Clusters and nebulæ, with a few exceptions, are apt to prove more or less disappointing in small instruments. The letters of the Greek alphabet are as follows:
[alpha] Alpha. [beta] Beta. [gamma] Gamma. [delta] Delta. [epsilon] Epsilon. [zeta] Zeta. [eta] Eta. [theta] Theta. [iota] Iota. [kappa] Kappa. [lambda] Lambda. [mu] Mu. [nu] Nu. [xi] Xi. [omicron] Omicron. [pi] Pi. [rho] Rho. [sigma] Sigma. [tau] Tau. [upsilon] Upsilon. [phi] Phi. [chi] Chi. [psi] Psi. [omega] Omega.
ANDROMEDA.
M. 31: 0 h. 37 m. + 40° 43′. Great Spiral Nebula. Visible to naked eye near [nu] Andromedæ. Rather disappointing in small glass.
[Sigma] 205 or [gamma] : 1 h. 58 m. + 41° 51′ : 3-5 : 62′5° : 10·2″. Yellow, bluish-green. 5 is also double, a binary, but a very difficult object at present.
AQUARIUS.
M. 2 : 21 h. 28 m. - 1° 16′. Globular cluster; forms flat triangle with [alpha] and [beta].
[Sigma] 2909 or [zeta] : 22 h. 24 m. -0° 32′ : 4-4·1 : 319·1° : 3·29″. Yellow, pale yellow. Binary.
AQUILA.
M. 11 : 18 h. 46 m. - 6° 23′. Fine fan-shaped cluster. Just visible to naked eye.
V : 18 h. 59 m. - 5° 50′. Red star, variable from 6·5 to 8·0.
ARGO NAVIS.
M. 46 : 7 h. 37 m. - 14° 35′. Cluster of small stars, about 1/2° in diameter.
ARIES.
[Sigma] 180 or [gamma] : 1 h. 48 m. + 18° 49′ : 4·2-4·4 : 359·4° : 8·02″. Both white. Easy and pretty.
[lambda] 1 h. 52 m. + 23° 7′ : 4·7-6·7 : 47° : 36·5″. Yellow, pointed to by [gamma] and [beta].
AURIGA.
(Capella) [alpha] : 5 h. 9 m. + 45° 54′. Spectroscopic binary; period 104 days.
M. 37 : 5 h. 46 m. + 32° 31′. Fine cluster. M. 36 and M. 38 also fine. All easily found close to straight line drawn from [kappa] to [phi] Aurigæ.
[beta] : 5 h. 52 m. + 44° 57′. Spectroscopic binary, period 3·98 days.
41: 6 h. 4 m. + 48° 44′ : 5·2-6·4 : 353·7 : 7·90″. Yellowish-white, bluish-white.
BOÖTES.
[Sigma] 1864 or [pi] : 14 h. 36 m. + 16° 51′ : 4·9-6 : 103·3° : 5·83″. Both white.
[Sigma] 1877 or [epsilon] : 14 h. 40 m. + 27° 30′ : 3-6·3 : 326·4° : 2·86″. Yellow, blue. Fine object and good test.
[Sigma] 1888 or [xi] : 14 h. 47 m. + 19° 31′ : 4·5-6·5 : 180·4° : 2·70″. Yellow, purple, binary.
[Sigma] 1909 or 44 : 15 h. 0 m. + 48° 2′ : 5·2-6·1 : 242° : 4·32″.
CAMELOPARDUS.
V. : 3 h. 33 m. + 62° 19′. Variable, 7·3 to 8·8. Fiery red.
CANCER.
[Sigma] 1196 or [zeta] : 8 h. 6 m. + 17° 57′ : 5-5·7-6·5 : 349·1°, 109·6° : 1·14″, 5·51″. Triple ; 5 and 5·7 binary, period 60 years; 6·5 revolves round centre of gravity of all in opposite direction.
[Sigma] 1268 or [iota] : 8 h. 41 m. + 29° 7′ : 4·4-6·5 : 307° : 30·59″. Yellow, blue.
Præsepe: Cluster, too widely scattered for anything but lowest powers.
CANES VENATICI.
[Sigma] 1622 or 2 : 12 h. 11 m. + 41° 13′ : 5-7·8 : 258° : 11·4″. Gold, blue.
[Sigma] 1645 : 12 h. 23 m. + 45° 21′ : 7-7·5 : 160·5° : 10·42″. White. Pretty, though faint.
[Sigma] 1692, 12, or [alpha] : 12 h. 51 m. + 38° 52′ : 3·1-5·7 : 227° : 19·69″. Cor Caroli. White, violet.
M. 51 : 13 h. 26 m. + 47° 43′. Great spiral. 3° S.W. of [eta] Ursæ Majoris.
M. 3 : 13 h. 38 m. + 28° 53′. Fine globular cluster; on line between Cor Caroli and Arcturus, rather nearer the latter.
CANIS MAJOR.
M. 41 : 6 h. 43 m. - 20° 38′. Fine cluster, visible to naked eye, 4° below Sirius.
CANIS MINOR.
(Procyon) [alpha] : 7 h. 34 m. + 5° 30′ : 0·5-14 : 5° 4·46″. Binary, companion discovered, Lick, 1896, only visible in great instruments.
CAPRICORNUS.
[alpha] : 20 h. 12 m. - 12° 50′ : 3·2-4·2. Naked eye double, both yellow.
M. 30 : 21 h. 35 m. - 23° 38′. Fairly bright cluster.
CASSIOPEIA.
[Sigma] 60 or [eta] : 0 h. 43 m. + 57° 18′ : 4-7 : 227·8° : 5·64″. Binary; period about 200 years.
[Sigma] 262 or [iota] : 2 h. 21 m. + 66° 58′ : 4·2-7·1-7·5 : 250°, 112·6° : 1·93″, 7·48″. Triple.
H. vi. 30 : 23 h. 52 m. + 56° 9′. Large cloud of small stars.
[Sigma] 3049 or [sigma] : 23 h. 54 m. + 55° 12′ : 5-7·5 : 325·9° : 3·05″. Pretty double, white, blue.
CEPHEUS.
[kappa] : 20 h. 12 m. + 77° 25′ : 4-8 : 123° : 7·37″. Yellowish-green.
[Sigma] 2806 or [beta] : 21 h. 27 m. + 70° 7′ : 3-8 : 250·6° : 13·44″. White, blue.
S : 21 h. 36 m. + 78° 10′. Variable, 7·4 to 12·3. Very deep red.
[Sigma] 2863 or [xi] : 22 h. 1 m. + 64° 8′ : 4·7-6·5 : 283·3°: 6·87″. Yellow, blue.
[delta] : 22 h. 25 m. + 57° 54′ : variable-5·3 : 192° : 40″. Yellow, blue. Primary varies from 3·7 to 4·9. Period, 5·3 days. Spectroscopic binary.
[Sigma] 3001 or [omicron] : 23 h. 14 m. + 67° 34′ : 5·2-7·8 : 197·3° : 2·97″. Yellow, yellowish-green.
CETUS.
(Mira) [omicron] : 2 h. 14 m. - 3° 26′. Variable. Period about 331 days. Maxima, 1·7 to 5; minima, 8 to 9. Colour, deep yellow to deep orange.
[Sigma] 281 or [nu] : 2 h. 31 m. + 5° 10′ : 5-9·4 : 83·1°: 7·74″. Yellow, ashy.
[Sigma] 299 or [gamma] : 2 h. 38 m. + 2° 49′ : 3-6·8 : 291° : 3·11″. Yellow, blue, slow binary.
COMA BERENICES.
[Sigma] 1657 or 24 : 12 h. 30 m. + 18° 56′ : 5·5-7 : 271·1° : 20·23″. Orange, blue.
M. 53 : 13 h. 8 m. + 18° 42′. Cluster of faint stars.
CORONA BOREALIS.
[Sigma] 1965 or [zeta] : 15 h. 36 m. + 36° 58′ : 4·1-5 : 304·3° : 6·15″. White greenish.
R : 15 h. 44 m. + 28° 28′. Irregularly variable, 5·5 to 10·1.
[Sigma] 2032 or [sigma] : 16 h. 11 m. + 34° 6′ : 5-6·1 : 216·3° : 4·80″. Yellow, bluish. Binary, period about 400 years.
CORVUS.
[delta] : 12 h. 25 m. - 15° 57′ : 3-8·5 : 214° : 24·3″. Yellow, lilac.
CRATER.
R. : 10 h. 56 m. - 17° 47′. Variable. About 8 magnitude. Almost blood-colour.
CYGNUS.
[Sigma] 2486 : 19 h. 9 m. + 49° 39′ : 6-6·5 : 218·2° : 9·63″. 'Singular and beautiful field' (Webb).
(Albireo) [beta] : 19 h. 27 m. + 27° 45′ : 3-5·3 : 55° : 34·2″. Orange-yellow, blue. Easy and beautiful.
[Sigma] 2580 or [chi] : 19 h. 43 m. + 33° 30′ : 4·5-8·1 : 71·6° : 25·50″. 4·5 is variable to 13·5. Period 406 days.
Z : 19 h. 58 m. + 49° 45′. Variable, 7·1 to 12. Deep red.
RS : 20 h. 10 m. + 38° 27′. Variable, 6 to 10. Deep red.
U : 20 h. 16 m. + 47° 35′. Variable, 7 to 11·6. Very red.
V : 20 h. 38 m. + 47° 47′. Variable, 6·8 to 13·5. Very red.
[Sigma] 2758 or 61 : 21 h. 2 m. + 38° 13′ : 5·3-5·9 : 126·8° : 22·52″. First star whose distance was measured.
RV : 21 h. 39 m. + 37° 33′. Variable, 7·1 to 9·3. Splendid red.
[Sigma] 2822 or [mu] : 21 h. 40 m. + 28° 18′ : 4-5 : 122·2° : 2·29″. Fine double; probably binary.
DELPHINUS.
[Sigma] 2727 or [gamma] : 20 h. 42 m. + 15° 46′ : 4-5 : 269·8° : 10·99″. Yellow, bluish-green.
V : 20 h. 43 m. + 18° 58′. Variable, 7·3 to 17·3. Period 540 days. Widest range of magnitude known.
DRACO.
[Sigma] 2078 or 17 : 16 h. 34 m. + 53° 8′ : 5-6 : 109·5° : 3·48″. White.
[Sigma] 2130 or [mu] : 17 h. 3 m. + 54° 37′ : 5-5·2 : 144·2° : 2·17″. White.
H. iv. 37 : 17 h. 59 m. + 66° 38′. Planetary nebula, nearly half-way between Polaris and [gamma] Draconis. Gaseous; first nebula discovered to be so.
[Sigma] 2323 or 39: 18 h. 22 m. + 58° 45′ : 4·7-7·7-7·1 : 358·2°, 20·8° : 3·68″, 88·8″. Triple.
[epsilon] : 19 h. 48 m. + 70° 1′ : 4-7·6 : 7·5° : 2·84″. Yellow, blue.
EQUULEUS.
[Sigma] 2737 or [epsilon] : 20 h. 54 m. + 3° 55′ : 5·7-6·2-7·1 : 285·9°, 73·8° : 0·53″, 10·43″. Triple with large instruments.
ERIDANUS.
[Sigma] 518 or 40 or 0^2 : 4 h. 11 m. - 7° 47′ : 4-9-10·8 : 106·3°, 73·6° : 82·4″, 2·39″. Triple, close pair binary.
GEMINI.
M. 35 : 6 h. 3 m. + 24° 21′. Magnificent cluster; forms obtuse triangle with [mu] and [eta].
[Sigma] 982 or 38 : 6 h. 49 m. + 13° 19′ : 5·4-7·7 : 159·7° : 6·63″. Yellow, blue. Probably binary.
[zeta] : 6 h. 58 m. + 20° 43′. Variable, 3·8 to 4·3. Period 10·2 days. Non-eclipsing binary.
[Sigma] 1066 or [delta] : 7 h. 14 m. + 22° 10′ : 3·2-8·2 : 207·3° : 6·72″. Pale yellow, reddish.
(Castor) [alpha] : 7 h. 28 m + 32° 7′ : 2-2·8 : 224·3° : 5·68″. White, yellowish-green. Finest double in Northern Hemisphere.
HERCULES.
M. 13 : 16 h. 38 m. + 36° 37′. Great globular cluster, two-thirds of way from [zeta] to [eta].
[Sigma] 2140 or [alpha] : 17 h. 10 m. + 14° 30′ : 3-6·1 : 113·6° : 4·78″. Orange-yellow, bluish-green. Fine object.
[Sigma] 2161 or [rho] : 17 h. 20 m. + 37° 14′ : 4-5·1 : 314·4° : 3·80″. 'Gem of a beautiful coronet' (Webb).
M. 92 : 17 h. 14 m. + 43° 15′. Globular cluster; fainter than M. 13.
[Sigma] 2264 or 95 : 17 h. 57 m. + 21° 36′ : 4·9-4·9 : 259·7° : 6·44″. 'Apple-green, cherry-red' (Smyth), but now both pale yellow.
[Sigma] 2280 or 100 : 18 h. 4 m. + 26° 5′ : 5·9-5·9 : 181·7° : 13·87″. Greenish-white.
HYDRA.
[Sigma] 1273 or [epsilon] : 8 h. 41 m. + 6° 48′ : 3·8-7·7 : 231·6° : 3·33″. The brighter star is itself a close double.
V : 10 h. 47 m. - 20° 43′. Variable, 6·7 to 9·5. Copper-red.
W : 13 h. 44 m. - 27° 52′. Variable, 6·7 to 8·0. Deep red.
LACERTA.
LEO.
[Sigma] 1424 or [gamma] : 10 h. 14 m. + 20° 21′ : 2-3·5 : 116·5° : 3·70″. Fine double, yellow, greenish-yellow.
[Sigma] 1487 or 54 : 10 h. 50 m. + 25° 17′ : 5-7 : 107·5° : 6·38″. Greenish-white, blue.
[Sigma] 1536 or [iota] : 11 h. 19 m. + 11° 5′ : 3·9-7·1 : 55·0° : 2·36″. Yellow, blue.
LEO MINOR.
LEPUS.
R : 4 h. 55 m. - 14° 57′. Variable, 6·7 to 8·5. Intense crimson.
LIBRA.
M. 5 : 15 h. 13 m. + 2° 27′. Globular cluster, close to star 5 Serpentis. Remarkable for high ratio of variables in it--1 in 11.
LYNX.
[Sigma] 948 or 12 : 6 h. 37 m. + 59° 33′ : 5·2-6·1-7·4 : 116°, 305·8° : 1·41″, 8·23″. Triple, greenish, white, bluish.
[Sigma] 1334 or 38 : 9 h. 13 m. + 37° 14′ : 4-6·7 : 235·6° : 2·88″. White blue.
LYRA.
T : 18 h. 29 m. + 36° 55′. Variable, 7·2 to 7·8. Crimson.
(Vega) [alpha] : 18 h. 34 m. + 38° 41′ : 1-10·5 : 160° : 50·77″. Very pale blue. The faint companion is a good test for small telescopes. Vega is near the apex of the solar way.
{ [epsilon]^1 : 18 h. 41·1 m. + 39° 30′ : 4·6-6·3 : 12·4° : 2·85″. [epsilon] { Pale yellow, pale orange yellow. { [epsilon]^2 : 4·9-5·2 : 127·3° : 2·15″. Both pale yellow.
[zeta] : 18 h. 41 m. + 37° 30′ : 4·2-5·5 : 150° : 43·7″. Easy, both pale yellow.
[beta] : 18 h. 46 m. + 33° 15′ : 3-6·7 : 149·8° : 45·3″. 3 variable, 12·91 days. Spectroscopic binary.
M. 57 : 18 h. 50 m. + 32° 54′. Ring Nebula, between [beta] and [gamma]. Faint in small telescope. Gaseous.
MONOCEROS.
[Sigma] 919 or 11 : 6 h. 24 m. - 6° 57′ : A 5-B 5·5-C 6 : AB 131·6° : 7·27″ : BC 105·7° : 2·65″. Fine triple.
[Sigma] 950 or 15 : 6 h. 35 m. + 10°·0′ : 6-8·8-11·2 : 212·2°, 17·9° : 2·69″, 16·54″. Triple, green, blue, orange.
OPHIUCHUS.
[rho] : 16 h. 19 m. - 23° 13′ : 6-6 : 355° : 3·4″.
39 : 17 h. 12 m. - 24° 11′ : 5·5-6 : 358° : 15″. Pale orange, blue.
[Sigma] 2202 or 61 : 17 h. 40 m. + 2° 37′ : 5·5-5·8 : 93·4° : 20·68″. White.
[Sigma] 2272 or 70 : 18 h. 1 m. + 2° 32′ : 4·5-6 : 178° : 2·10″. Yellow, purple. Rather difficult.
ORION.
(Rigel) [beta] : 5 h. 10 m. -8° 19′ : 1-8 : 202·2° : 9·58″. Bluish-white, dull bluish. Fair test for small glass.
[delta] : 5 h. 27 m. - 0° 23′ : 2-6·8 : 359° : 52·7″. White, very easy.
[Sigma] 738 or [lambda] : 5 h. 30 m. + 9° 52′ : 4-6 : 43° 1′ : 4·55″. Yellowish, purple. Pretty double.
[theta] : 5 h. 30 m. - 5° 28′ : 6-7-7·5-8. The 'Trapezium' in the Great Nebula.
M. 42 : 5 h. 30 m. - 5° 28′ : 6-7-7·5-8. Great Nebula of Orion.
[Sigma] 752 or [iota] : 5 h. 30 m. - 5° 59′ : 3·2-7·3 : 141·7° : 11·50″. White, fine field.
[sigma] : 5 h. 34 m. - 2° 39′. Fine multiple, double triple in small glass.
[zeta] : 5 h. 36 m. - 2° 0′ : 2-6 : 156·3° : 2·43″. Yellowish-green, blue.
U : 5 h. 50 m. + 20° 10′. Variable, 5·8-12·3. Period 375 days.
PEGASUS.
M. 15 : 21 h. 25 m. + 11° 43′. Fine globular cluster, 4° N.E. of [delta] Equulei.
PERSEUS.
H. VI. 33·34 : 2 h. 13 m. + 56° 40′. Sword-handle of Perseus. Splendid field.
M. 34 : 2 h. 36 m. + 42° 21′. Visible to naked eye. Fine low-power field.
[Sigma] 296 or [theta] : 2 h. 37 m. + 48° 48′ : 4·2-10-11 : 299°, 225° : 17·4″, 80″. Triple.
[Sigma] 307 or [eta] : 2 h. 43 m. + 55° 29′ : 4-8·5 : 300° : 28″. Orange-yellow, blue.
(Algol) [beta] : 3 h. 2 m. + 40° 34′. Variable, 2·1 to 3·2. Period 2·8 days. Spectroscopic eclipsing binary.
[Sigma] 464 or [zeta] : 3 h. 48 m: + 31° 35′ : 2·7-9·3 : 206·7° : 12·65°. Greenish-white, ashy. Three other companions more distant.
[Sigma] 471 or [epsilon] : 3 h. 51 m. + 39° 43′ : 3·1-8·3 : 7·8° : 8·8″. White, bluish-white.
PISCES.
[Sigma] 12 or 35 : 0 h. 10 m. + 8° 16′ : 6-8 : 150° : 12″. White, purplish.
[Sigma] 88 or [psi] : 1 h. 0·4 m. + 20° 56′ : 4·9-5 : 160° : 29·96″. White.
[Sigma] 100 or [zeta] : 1 h. 8 m. + 7° 3′ : 4·2-5·3 : 64° : 23·68″. White, reddish-violet.
[Sigma] 202 or [alpha] : 1 h. 57 m. + 2° 17′ : 2·8-3·9 : 318° : 2·47″. Reddish, white.
SAGITTA.
SAGITTARIUS.
M. 20 : 17 h. 56 m. - 23° 2′. The Trifid Nebula.
SCORPIO.
[beta] : 15 h. 59·6 m. - 19° 31′ : 2-5 : 25° : 13·6″. Orange, pale yellow.
(Antares) [alpha] : 16 h. 23 m. - 26° 13′ : 1-7 : 270° : 3″. Difficult with small glass.
SCUTUM SOBIESKII.
M. 24 : 18 h. 12 m. - 18° 27′. Fine cluster of faint stars on Galaxy.
M. 17 : 18 h. 15 m. - 16° 14′. The Omega Nebula. Gaseous.
R : 18 h. 42 m. - 5° 49′. Irregular, variable, 4·8 to 7·8.
SERPENS.
[Sigma] 1954 or [delta] : 15 h. 30 m. + 10° 53′ : 3·2-4·1 : 189·3° : 3·94″. Yellow, yellowish-green, binary.
[Sigma] 2417 or [theta] : 18 h. 51 m. + 4° 4′ : 4-4·2 : 103° : 22″. Both pale yellow.
SEXTANS.
TAURUS.
[Sigma] 528 or [chi] : 4 h. 16 m. + 25° 23′ : 5·7-7·8 : 24·2° : 19·48″. White, lilac.
[Sigma] 716 or 118 : 5 h. 23 m. + 25° 4′ : 5·8-6·6 : 201·8 : 4·86″. White, bluish-white.
M. 1 : 5 h. 28 m. + 21° 57′. The Crab Nebula. Faint in small glass.
TRIANGULUM.
[Sigma] 227 or [iota] : 2 h. 7 m. + 29° 50′ : 5-6·4 : 74·6°: 3·79″. Yellow, blue, beautiful.
URSA MAJOR.
[Sigma] 1523 or [xi] : 11 h. 13 m. + 32° 6′ : 4-4·9 : 137·2° : 2·62″. Yellowish, binary. Period 60 years.
[Sigma] 1543 or 57 : 11 h. 24 m. + 39° 54′ : 5·2-8·2 : 2·1° : 5·40″. White, ashy.
(Mizar) [zeta] : 13 h. 20 m. + 55° 27′ : 2·1-4·2 : 149·9° : 14·53″. Fine pair, yellow and yellowish-green. Alcor, 5 magnitude in same field with low power, also 8 magnitude star.
URSA MINOR.
(Polaris) [alpha] : 1 h. 22 m. + 88° 46′ : 2-9 : 215·6° : 18·22″. Yellow, bluish, test for 2-inch.
VIRGO.
[Sigma] 1670 or [gamma] : 12 h. 37 m. - 0° 54′ : 3-3 : 328·3° : 5·94″. Both pale yellow. Binary, 185 years.
VULPECULA.
M. 27 : 19 h. 55 m. + 22° 27′. The Dumb-bell Nebula. Just visible with 1-1/4-inch. Gaseous.
INDEX
A
Achromatic. See Telescope
Adams, search for Neptune, 198-201
Aerolites, 227
Airy, search for Neptune, 197-201
Albireo, colour of, 236
Alcor, 241
Alcyone, 256
Aldebaran, 234; colour of, 235
Algol, spectroscopic binary, 246; diameter and mass of components, 246; period of, 250; variables, 250
Alps, lunar, 116; valley of, 116, 117
Altai Mountains, 117
Altair, 234
Altazimuth, 25-28
Anderson discovers Nova Aurigæ, 253; discovers Nova Persei, 254
Andromeda, great nebula of, 263, 264
Andromedæ [gamma], colour of, 236
Andromedes, 214, 215, 225, 226
Annular eclipse, 69, 70
Antares, 234
Anthelme observes new star, 252
Apennines, lunar, 116
Archimedes, 117
Arcturus, 234
Argelander, number of stars, 235
Ariadæus cleft, 119
Arided, 234
Arietis [gamma], observed by Hooke, 240
Aristillus, 117
Asteroids, number of, 150; methods of discovery, 150, 151
Asterope, 256
Astræa, discovery of, 150
Atlas, 256
Atmosphere, solar, 75
Autolycus, 117
Auzout, aerial telescopes, 4
B
Bacon, Roger, 1
Bailey, cluster variables, 259
Ball, Sir R., 154, 262; 'Popular Guide to the Heavens,' 278
Barnard, measures of Venus, 89; markings on Venus, 95; on Mars, 133; measures of asteroids, 152; discovers Jupiter's fifth satellite, 167; measures of Saturn, 172; drawing of Saturn, 172; rotation of Saturn, 174; on Saturnian markings, 184-185; observation of Comet 1882 (iii.), 218
Bayer, lettering of stars, 278
Beer. See Mädler
Bélopolsky, rotation of Venus, 96
Bessel, search for Neptune, 197
Betelgeux, 234; colour of, 235
Biela's comet, 213, 214, 215, 224, 225
Birmingham observes Nova Coronæ, 252
Bode's law, 148, 149
Bond, G. P., discovers rifts in Andromeda nebula, 264
Bond, W. C., discovers Crape Ring, 178; discovers Saturn's eighth satellite, 187; verifies discovery of Neptune's satellite, 201
Boötis [epsilon], double star, 242
Bouvard, tables of Uranus, 197
Bradley uses aerial telescope, 4
Bremiker's star-charts, 200
Brooks' comet, 210; observation of comet 1882 (iii.), 218
Brorsen's comet, 213
C
Calcium in chromosphere, 73
Campbell, atmosphere of Mars, 140; bright projections on Mars, 141; spectroscopic investigation of Saturn's rings, 180
Canals. See Mars
Canes Venatici, great spiral nebula in, 265
Canopus, 234
Capella, 234
Capricorni [alpha], naked-eye double, 241
Carpathians, 117
Carrington, solar rotation, 59
Cassegrain. See Telescope, forms of
Cassini uses aerial telescope, 4; discovers four satellites of Saturn and division of ring, 4; observations on Jupiter, 160; discovers division in Saturn's ring, 177; four satellites of Saturn, 184, 186, 187
Cassiopeiæ [eta], double star, 242; Nova, 252
Castor, 234; double star, 242; binary, 245
Caucasus, lunar, 116
Cauchoix constructs 12-inch O.G., 6
Celaeno, 256
Celestial cycle, 18
Centauri [alpha], 231, 234
Ceres, discovery of, 149; diameter of, 152; reflective power, 152
Ceti [zeta], naked-eye double, 241; Mira ([omicron]) variable star, 248; period, 249
Challis, search for Neptune, 199
Chambers, G. F., on comets, 208-209; number of comets, 209
Chromosphere, 71, 73, 76; depth of, 73; constitution of, 73
Clark, Alvan, constructs 18-1/2-inch, 8; 26-inch, 8; 30-inch Pulkowa telescope and 36-inch Lick, 8; 40-inch Yerkes, 9
Clavius, lunar crater, 113, 114, 120
Clerke, Miss Agnes, 60, 73; climate of Mercury, 85; on Mars, 139; albedo of asteroids, 152; Jupiter's red spot, 161; on comet 1882 (iii.), 218; on Mira Ceti, 248
Clerk-Maxwell, constitution of Saturn's rings, 179
Cluster variables, 259
Clusters, irregular, 256; globular, 258
Coggia's comet, 211
Coma Berenices, 256
Comas Solà, rotation of Saturn, 174
Comet of 1811, 206; of 1843, 206, 215, 216; of Encke, 207; of Halley, 207, 213; Brooks, 210; Donati, 205, 210; Tempel, 211; 1866 (i.), 214, 224; Winnecke, 211; Coggia, 211; Holmes, 211; Biela, 213; and Andromeda meteors, 214, 215, 224, 225; great southern (1901), 211; Wells, 213; of 1882, 213, 216-219; De Vico, 213; Brorsen, 213; of Swift 1862 (iii.), and Perseid meteors, 214, 224; great southern (1880), 216; of 1881, 216; of 1807, 216
Comets, 203 _et seq._; structure of, 205; classes of, 206-208; number of, 209; spectra of, 211-213, 218; constitution of, 212, 218; connection with meteors, 214, 215, 224; families of, 215-218; observation of, 219-222
Common 5-foot reflector, 12; photographs Orion nebula, 262
Constellations, formation of, 237, 238
Contraction of sun, 79
Cooke, T., and Sons, 25-inch Newall telescope, 8; mounting of 6-inch refractor, 31
Copernicus, prediction of phases of Venus, 92; lunar crater, 114; ray system of, 120, 121
Corona, 71, 72, 76; tenuity of, 71; variations in structure, 71; minimum type of, 71, 72; maximum type of, 72; constitution of, 72
Corona Borealis, 238; Nova in, 252
Coronal streamers, analogy with Aurora, 71
Coronium, 72, 73
Cottam, charts of the constellations, 278
Crape ring of Saturn, 178
Craters, lunar, 109, 112; ruined and 'ghost,' 111; number and size, 112; classification of, 112
Cygni, 61, 231; [alpha], 234; [beta], colour of, 236
D
Darwin, G. H., evolution of Saturnian system, 186
Dawes discovers crape ring, 178; search for Neptune, 199, 200
Deimos, satellite of Mars, 143
Delphinus, 237
Denning, absence of colour in reflector, 22; measuring sun-spots, 51, 53; on naked-eye views of Mercury, 82; abnormal features on Venus, 94; on canals of Mars, 136; observations of cloud on Mars, 139, 140; changes on Jupiter, 159, 160; rotation of Saturn, 174; visibility of Cassini's division, 182; number of meteor radiants, 225; classification of sporadic meteors, 227; meteoric observation, 227, 228; stationary radiants, 229
Deslandres, calcium photographs of sun, 60; on form of corona, 72; photographs chromosphere and prominences, 74
De Vico's comet, 213
Dew-cap, 39
Digges, supposed use of telescopes, 1
Dollond, John, invention of achromatic, 5; 5-foot achromatics, 6
Donati, comet of 1858, 205, 210; spectrum of comet Tempel, 211
Doppler's principle, 180
Dorpat refractor, 6, 7, 31
Douglass, markings on Venus, 95
Draco, planetary nebula in, 266
Dunér, rotation of sun, 59
E
Earth-light on moon, 105
Eclipse, Indian, 1898, 70; 1878, July 29, 72; 1870, December 22, 74
Eclipses, solar, 68-70; of moon, 105, 106
Electra, 256
Electrical influence of sun on earth, 63
Elger on lunar Maria, 111; lunar clefts, 119; lunar chart, 125
Elkin observes transit of comet 1882 (iii.), 212
Encke discovers division in ring of Saturn, 177; search for Neptune, 200
Equatorial mountings, 29-31, 36
Equulei [delta], short-period binary, 245
Erck, Dr. Wentworth, satellites of Mars, 144
Eros, discovery of, distance of, 151; variability of, 152
F
Fabricius observes Mira Ceti, 248
Faculæ, 59; rotation period of, 59
Faculides, 60
Finder. See Telescope
Finlay, transit of comet 1882 (iii.), 212
Flamsteed, catalogue of stars, 278
Fomalhaut, 234
Fowler, 'Telescopic Astronomy,' 17
Fracastorius, 111
G
Galaxy. See Milky Way
Galilean telescope. See Telescope, forms of
Galileo Galilei, invention of telescope, 2; loss of sight, 47; discovery of phases of Venus, 92; on lunar craters, 112; discovers four satellites of Jupiter, 166; observations of Saturn, 175, 176
Galle discovers Neptune, 200
Gassendi observes transit of Mercury, 87; lunar crater, 119
Geminorum [alpha]. See Castor
George III. pensions Herschel, 193
Georgium Sidus, 194
Gore, period of Algol, 250; globular clusters, 259; 'The Stellar Heavens,' 278
Gregorian. See Telescope, forms of
Grubb, 27-inch Vienna telescope, 8; on telescopic powers, 41
Gruithuisen, changes on moon, 126
H
Hale, calcium photographs of sun, 60
Hall, Asaph, discovers satellites of Mars, 8, 143; rotation of Saturn, 173, 174
Hall, Chester Moor, discovers principle of achromatic, 5
Halley's comet, 207, 213
Harding discovers Juno, 149
Hebe, discovery of, 150
Hegel proves that there are only seven planets, 149
Helium in chromosphere, 73
Helmholtz, speed of sensation, 48; solar contraction, 79
Hencke discovers Astræa and Hebe, 150
Henry, 30-inch Nice telescope, 8
Heraclides promontory, 117
Hercules, 237
Herculis [alpha], double star, 242
Herodotus, valley of, 118, 119, 126
Herschel, Sir John, drawing of Orion nebula, 262
Herschel, Sir William, 4-foot telescope, 13; impairs sight, 47; misses satellites of Mars, 143, 144; rotation of Saturn, 173; discovers Saturn's sixth and seventh satellites, 186, 187; early history, 190, 191; discovers Uranus, 191; discovers two satellites of Uranus, 196; binary stars, 244; gaseous constitution of nebulæ, 260; distribution of nebulæ, 267; translation of solar system, 269
Herschelian. See Telescope, forms of
Hevelius, description of Saturn, 176
Hind discovers Nova Ophiuchi, 252
Hirst, colouring of Jupiter, 159
Hirst, Miss, colouring of Jupiter, 159
Holden on solar rotation, 59, 60
Holmes, Edwin, telescope-house, 38; comet, 211
Holmes, Oliver Wendell, 'Poet at the Breakfast-table,' 13
Holwarda observes [omicron] Ceti, 248
Hooke, observation of Gamma Arietis, 240
Howlett, criticism of Wilsonian theory of sun-spots, 61
Huggins, atmosphere of Mars, 140; gaseous nature of nebulæ, 210; spectrum of Winnecke's comet, 211; discovers nebula in Draco to be gaseous, 260; spectrum of Andromeda nebula, 264
Humboldtianum, Mare, 111
Humboldt observes meteor-shower of 1799, 224
Hussey, search for Neptune, 197
Hussey, W. J., period of [delta] Equulei, 245
Huygens, improvement on telescopes, 3; aerial telescopes, 4; discovers nature of Saturn's ring and first satellite of Saturn, 177, 186; observation of [theta] Orionis, 240; of great nebula in Orion, 261
Huygens, Mount, 116
Hydrogen in chromosphere, 73
Hyginus cleft, 119
I
Imbrium, Mare, 116
Iron in chromosphere, 73
J
Jansen, Zachariah, claim to invention of telescope, 1
Janssen, photographs of sun, 57
Journal of British Astronomical Association, 23, 38
Juno, discovery of, 149; diameter of, 152
Jupiter, brilliancy compared with Venus, 90; period of, 155; distance of, 155; diameter of, 155; compression, volume, density, 155; brilliancy, 156; apparent diameter of, 156; belts of, 157 _et seq._; colouring, 158, 159; changes on surface of, 159, 160; great red spot, 160-164; rotation period, 163-165; resemblance to sun, 164-166; satellites of, 166-169; observation of, 169-171; visibility of satellites, 166; diameters of, 167; occultations of, eclipses of, transits of, 167
K
Kaiser sea, Mars, 145
Keeler, report on Yerkes telescope, 9; rotation of Saturn, 174; constitution of Saturn's rings, 180; photographic survey of nebulæ, 267
Kelvin, solar combustion, 78, 79
Kepler, suggestion for improved refractor, 3; predicts transit of Mercury, 87; lunar crater, ray-system of, 120, 121; observes new star, 252
Kirchhoff, production of Fraunhofer lines, 75
Kirkwood, theory of asteroid formation, 153; periodic meteors, 214
Kitchiner, visibility of Saturn's satellites, 188
Klein's Star Atlas, 255
L
Lampland, photographs of Mars, 137
Langley, heat of umbra of sun-spot, 50; changes in sunspots, 55
Lassell, 4-foot reflector, 37; discovers Saturn's eighth satellite, 187; discovers satellite of Uranus, 196; search for Neptune, 200; discovers satellite of Neptune, 201; drawing of Orion nebula, 262
Leibnitz, mountains, 117
Lemonnier, observations of Uranus, 193
Leonid, meteors, 214, 224, 225, 226
Leonis [gamma], colour of, 236
Leverrier, search for Neptune, 199-201
Lewis, revision of Struve's 'Mensuræ Micrometricæ,' 278
Lick, 36-inch telescope, 8
Light, speed of, 231
Light-year, 230
Lippershey, claim to invention of telescope, 1
Lohrmann, lunar chart of, 122
Lowell, rotation of Mercury, 85; surface of Mercury, 86; surface of Venus, 95; rotation of Venus, 96; 'oases' of Mars, 137, 138; projections on Mars, 141
Lunar observation, 123-125
Lyræ [epsilon], double double, 241, 242; [beta], variable star, 249; spectroscopic binary, 250
Lyra, ring nebula in, 265; photographs of, 266
Lyrid, meteors, 214, 224, 226
M
M. 35, cluster, 257; M. 13, number of stars in, 258; M. 92, 259; M. 3 and M. 5, variables in, 259; M. 51, 265
MacEwen, drawing of Venus, 94, 95
Mädler, heights of lunar mountains, 118; lunar chart, 122, 124, 128
Maginus, 120
Magnesium in chromosphere, 73
Maia, 256
Maintenance of solar light and heat, 78, 79
Marius, Simon, description of Andromeda nebula, 264
Markwick, Colonel, 117
Mars, distance, diameter, rotation, year of, phase of, 130-132; oppositions of, 130, 131; polar caps, 132; canals, 135-137; dark areas, 133; 'oases,' 137, 138; atmosphere of, 139, 140; projections on terminator, 141; satellites of, 142-144; visibility of details of, 144
Maunder, Mrs., photographs of coronal streamers, 70
Maunder, E. W., adjustment of equatorial, 22, 23; electrical influence of sun on earth, 63; 'Astronomy without a Telescope,' 238
Mee, Arthur, on amateur observation, 17; visibility of Cassini's division, 183
Melbourne 4-foot reflector, 12
Mellor, lunar chart, 124
Mendenhall, illustration of sun's distance, 48
Mercury, elongations of, 81; diameter of, 82; orbit, 83; bulk, weight, density, reflective power, 83; phases, 84; surface, 84; rotation period, 85; transits, 87, 88; anomalous appearances in, 87
Merope, 256
Merz, Cambridge (U.S.A.), and Pulkowa refractors, 6
Messier, lunar crater, 126; 'the comet ferret,' 219; catalogue of nebulæ, 258
Meteors, 222 _et seq._; shower of 1833, 223; of 1866, 224; Perseid, 214, 224, 225; Leonid, 214, 224, 225; Lyrid, 214, 224, 226; Andromedes, 214, 215, 224, 225; radiant point, 223, 224; sporadic, 226; observation of, 227-229
Metius's claim to invention of telescope, 1
Milky Way, 239; clustering of stars towards, 240; nebulæ in, 240
Mira, [omicron] Ceti, 248; period of, 249
Mizar, 240, 241
Montaigne, 219
Month, lunar and sidereal, 103
Moon, size, orbit, area, volume, density, mass, force of gravity, 100; lunar tides, 101, 102; phases, 102; synodic period, 103; reflective power, 104; 'old moon in young moon's arms,' 104; earth's light on, 105; lunar eclipses, 105, 106; 'black eclipses,' 105; Maria of, 109-111; craters of, 109, 112-114; mountain ranges, 109, 116-118; clefts or rills, 109, 118, 119; ray systems, 109, 120, 121; atmosphere of, 126; evidence of change, 127, 128
Mountings. See Telescope
N
Nasmyth, willow-leaf structure of solar surface, 57; lunar clefts, 119; on lunar ray systems, 121; and Carpenter, lunar chart, 125; on powers for lunar observation, 127
Nebula of Orion, 261-263; drawings of, 262; photographs, 262; distance of, 263; of Andromeda, 263, 264; photographs of, 264; spectrum, 264
Nebulæ, few in neighbourhood of Galaxy, 240; Messier's catalogue of, 258; gaseous, 260 _et seq._; spiral, 263-265; ring, 265; planetary, 266; number of, 267
Neison on lunar walled plains, 115, 120; lunar chart, 125
Neptune, 148, 196 _et seq._; diameter, distance, period, spectrum, satellite of, 201
Newall, 25-inch refractor, 8
Newcomb on scale of solar operations, 77, 78; on markings of Venus, 93; phosphorescence of dark side of Venus, 97; ratio of stellar increase, 235; 'Astronomy for Everybody,' 238; stars in galaxy, 240; spectroscopic binaries, 248; on Nova Persei, 254; on constitution of stars, 268; apex of solar path, 271
Newton, Sir Isaac, invents Newtonian reflector, 10
Nice, 30-inch refractor, 8
Nichol on M. 13, 258
Nilosyrtis, 145
Noble, method of observing sun, 67; visibility of Saturn's satellites, 188
Nova Cassiopeiæ, 252; Coronæ, 252; Cygni, 253; Andromedæ, 253; Ophiuchi, 252; Aurigæ, 253; spectrum of, 253; changes into planetary nebula, 254; Persei, 254; photographs of, 254; nebulosity round, 254; Geminorum, 255; colour, spectrum of, 255
O
Object-glass, treatment of, 19, 20; testing of, 20-23
Observation, methods of solar, 65-67
Olbers discovers Pallas and Vesta, 149; theory of asteroid formation, 150, 152
Oppolzer, E. von, discovers variability of Eros, 152
Opposition, 130 (note); of Mars, 130, 131
Orion, 237; great nebula of, 261-263
Orionis [theta], observation of, 240; [iota], naked-eye double, 241; [theta], multiple star, 243; [sigma], multiple star, 243
P
Palisa discovers asteroids, 151
Pallas, discovery of, 149; diameter of, 152
Peck, 'Constellations and How to Find Them,' 238; star-charts, 278
Pegasi [kappa], short-period binary, 245
Pegasus, 237
Perihelion of planets, 131 (note)
Period, synodic, of moon, 103
Perrine discovers Jupiter's sixth and seventh satellites, 167
Perseid, meteors, 214, 224, 225
Perseus, sword-handle of, 257
Petavius cleft, 119
Peters discovers asteroids, 151
Phillips, Rev. T. E. R., polar cap of Mars, 134; canals of Mars, 137; clouds on Mars, 140
Phobos satellite of Mars, 143
Phosphorescence of dark side of Venus, 97
Photosphere, 75
Piazzi discovers Ceres, 149
Pickering, E. C., number of lucid stars in northern hemisphere, 233; parallax of Orion nebula, 262
Pickering, W. H., on lunar ray systems, 120, 121; changes on moon, 126; on polar cap of Mars, 134, 135; discovers Saturn's ninth and tenth satellites, 187; photographs Orion nebula, 262
Planetary nebulæ, 266; spectra of, 266; nebula in Draco, 266
Plato, 117, 126
Pleiades, number of stars in, 233, 256, 257; nebula of, 257
Pleione, 256
Polarizing eye-piece, 66
Pollux, 234
Præsepe, 256
Procellarum Oceanus, 111
Proctor, 2; method of finding Mercury, 82; on state of Jupiter, 166
Proctor on the Saturnian system, 181; visibility of Cassini's division, 182; on Challis's search for Neptune, 199; Star Atlas, 278
Procyon, 234
Projecting sun's image, 67
Projections on terminator of Mars, 141
Prominences, 73, 74
Ptolemäus, 112
Pulkowa, 30-inch refractor, 8, 9
R
Radiant point of meteors, 223, 224; number of, 225; stationary, 229
Ranyard Cowper on parallax measures, 231
Regulus, 234
Reversing layer seen by Young, 74; spectrum photographed by Shackleton, 75; depth of, 75
Riccioli observes duplicity of [zeta] Ursæ Majoris, 240
Rigel, 232, 234; colour of, 235
Ritchey, 5-foot reflector Yerkes Observatory, 12
Roche's limit, 186
Rosse, Earl of, 6-foot reflector, 12; colouring of Jupiter, 158, 159; telescope, resolution of Orion nebula, 260; drawing of Orion nebula with, 262; spiral character of M. 51, 265
Rotation period of Mercury, 85; of Venus, 95, 96
S
Satellite of Venus, question of, 97, 98; of Mars, 142-144; of Jupiter, 166-169
Saturn, orbit of, sun-heat received by, period of, diameter of, compression and density of, 172; features of globe, rotation period, 173; varying aspects of rings, 178; measures of rings, 178; constitution of rings, 179; satellites of, 186-189; satellites, transits of, 189
Scheiner, construction of refractors, 2
Scheiner, Julius, spectrum of Andromeda nebula, 264
Schiaparelli, rotation of Mercury, 85; surface of Mercury, 86; rotation of Venus, 96; discovery of Martian canals, 135-137; connection of comets and meteors, 214, 224
Schmidt, lunar map, 114; observation of comet 1882 (iii.), 217, 218; observes Nova Cygni, 253
Schröter, observations of Venus, 94; lunar mountains, 118; rills, 118; lunar atmosphere, 126
Schwabe, discovery of sun-spot period, 61, 62
See, Dr., duration of sun's light and heat, 80
Serenitatis, Mare, serpentine ridge on, 110, 111; crossed by ray from Tycho, 120
Shackleton photographs spectrum of reversing layer, 75
Sidereal month, 103
Siderites and siderolites, 227
Sinus Iridum, 117
Sirius, companion of, discovered, 8; brightness, 234; colour, 235; brilliancy compared with Venus, 90; with Jupiter, 156
Sirsalis cleft, 119
Smyth, Admiral, on amateur observers, 18, 19, 45
Sodium in chromosphere, 73
Solar system, translation of, 269-272
South, Sir James, 12-inch telescope, 6
Spectroscope, 73, 76
Spectroscopic observations of rotation of Venus, 96; of Martian atmosphere, 140; investigations of Saturn's rings, 180; of Uranus, 195
Spectrum of reversing layer, 75; of chromosphere, 73
Spencer, Herbert, relation of stars and nebulæ, 267
Spica Virginis, 234
Stars, distance of, 231; number of, 232, 233; magnitudes, 234; numbers in different magnitudes, 235; colours, 235-237; change of colour in, 236, 237; constellations, 237, 238; double, 240; multiple, 243; binary, 244; spectroscopic binaries, 245-248; variable, 248-251; new or temporary, 251-255; constitution of, 268
Struve, F. G. W., 'Mensuræ Micrometricæ,' 278
Struve (Otto) discovers satellite of Uranus, 196; verifies discovery of Neptune's satellite, 201
Sun, size, distance, 47, 48; rotation period of, 57-59; methods of observing, 65-67; atmosphere of, 75; light and heat of, 78
Sun-spots, 49, 50; rapid changes in, 54, 55; period of, 62; zones and variation of latitude of, 62
Synodic period, 103
Syrtis Major, 145
Swift, Dean, satellites of Mars, 142
Swift's comet, 214, 224
T
Taygeta, 256
Telescope, invention of, 1, 2; refracting, 3; achromatic, 5; reflecting, 10, 11; forms of reflecting, Newtonian, Gregorian, Herschelian, Cassegrain, 10, 11; mirrors of reflecting, 11, 12; finders, 23, 24; mountings of, Altazimuth, 25-28; equatorial, 30, 31; house for, 37, 38; management of, 39, 40; powers of, 40, 41
Tempel's comet, 211
Terminator of moon, 107; of Venus, 94
Titius, discovery of Bode's law, 148
Turner discovers Nova Geminorum, 255
Tycho, 114; ray-system of, 108, 120, 121; Brahé observes Nova Cassiopeiæ, 252
U
Uranus, 190; distance from sun, period, diameter, visibility, 194; spectrum and density, 195; satellites, 196
Ursæ Majoris [zeta], duplicity of, 240; [xi] binary, 244; spectroscopic binary, 247
V
Variable stars, 248-251
Variation in sun-spot latitude, 62
Vega, 234; colour of, 235; apex of solar path, 271
Venus, diameter, 89; orbit and elongations, 89; visibility of, 89, 90; brilliancy, 90; reflective power, 90; phases, 92; as telescopic object, 93; atmosphere, 93; blunting of south horn, 94; rotation period, 96; 'phosphorescence' of dark side, 97; question of satellite of, 97, 98; transits, 98; opportunities for observation, 98, 99
Vesta, discovery of 149; diameter of, 152; reflective power, 152
Vienna, 27-inch refractor, 8
Vogel, atmosphere of Mars, 140; discovery of spectroscopic binaries, 245, 246
W
Washington, 26-inch refractor, 8
Watson, asteroid discoveries, 151, 153
Webb, Rev. J. W., remarks on telescope, 17; on amateurs, 18; on cleaning of eye pieces, 20; visibility of Saturn's rings, 181; lunar chart, 124; 'Celestial Objects,' 124; colouring of Jupiter, 158; description of planetary nebula in Draco, 267
Williams, A. Stanley, seasonal variations in colour of Jupiter's belts, 159; periods of rotation (Jupiter), 163; rotation of Saturn, 174
Wells's comet, 213
Wilson, theory of sun-spots, 60, 61
Winnecke's comet, 211
Wolf, asteroid discoveries, 151
Y
Yerkes observatory, 40-inch refractor, 8, 9; 5-foot reflector, 12
Young, illustrations from 'The Sun,' 48; electric influence of sun on earth, 63; observations of prominences, 74; of reversing layer, 74
Z
Zöllner, reflective power of Jupiter, 156
THE END
BILLING AND SONS, LTD., PRINTERS, GUILDFORD.
Transcriber's Note
- - indicates italic print; = = indicates bold print; + + indicates Old English font; ^ or ^{} indicates a superscript. ° indicates hours (or degrees); ′ indicates minutes (prime = minutes = feet); ″ indicates seconds (double prime = seconds = inches).
Sundry missing or damaged punctuation has been repaired.
Illustrations (or Plates) which interrupted paragraphs have been moved to more convenient positions between paragraphs.
A few words appear in both hyphenatd and unhyphenated versions. A couple have been corrected, for consistency; the others have been retained.
Page x: 'XI' corrected to 'IX'
"IX. THE ASTEROIDS 148"
Page 4: Corrected 'lengthwas' to 'length was'.
"... with a glass whose focal length was 212-1/4 feet."
Page 25: 'familar' corrected to 'familiar'.
"... or, to use more familiar terms,..."
Page 90: "... more especially if the object casting the shadow have a sharply defined edge,..."
'have' is correct, and has been retained (subjunctive after 'if').
Page 92: 'firstfruits' corrected to 'first-fruits'. (OED, and matches 2 other occurrences.)
"The actual proof of the existence of these phases was one of the first-fruits which Galileo gathered by means of his newly invented telescope."
Page 109: 'eyeryone' corrected to 'everyone'.
"... --'the man in the moon'--with which everyone is familiar."
Page 118: 'of' added - missing at page-turn.
"They embrace some of the loftiest lunar peaks reaching...."
Page 128: 'lnnar' corrected to 'lunar'.
"The lunar night would be lit by our own earth,..."
Page 157: 'imch' corrected to 'inch'.
"[Illustration: FIG. 25.
JUPITER, October 9, 1891, 9.30 p.m.; 3-7/8-inch, power 120.]"
Page 158: 'eyepiece' corrected to 'eye-piece', to match all the rest.
"... and a single lens eye-piece giving a power of 36."
Page 205: removed extraneous 'of'.
"The nucleus is the only part of [of] a comet's structure"
Page 209: 'unconsidreed' corrected to 'unconsidered'.
"... that some unconsidered little patch of haze...."
Page 240: 'Ursae' corrected to 'Ursæ' to match entries in the Index, and for consistency.
"... though Riccioli detected the duplicity of Zeta Ursæ Majoris (Mizar), in 1650,..."
Page 248: 'in once and a half times,'. 'once' is as printed (and may have been intended). As it is part of a quote, it has been retained.
"'Once in eleven months,' writes Miss Clerke, 'the star mounts up in about 125 days from below the ninth to near the third, or even to the second magnitude; then, after a pause of two or three weeks, drops again to its former low level in once and a half times, on an average, the duration of its rise.'"
Page 256: Page 256: 'Celæno' appears here in the text; 'Celaeno, 256' is the Index entry. Both are as printed.
Page 281: '285·9″' corrected to '285·9°'
"EQUULEUS.
[Sigma] 2737 or [epsilon] : 20 h. 54 m. + 3° 55′ : 5·7-6·2-7·1 : 285·9°, 73·8° : 0·53″, 10·43″. Triple with large instruments."
This follows the pattern of preceding
DRACO.
[Sigma] 2323 or 39: 18 h. 22 m. + 58° 45′ : 4·7-7·7-7·1 : 358·2°, 20·8° : 3·68″, 88·8″. Triple.
Page 282: '3·80°' corrected to '3·80″' to match pattern.
"[Sigma] 2161 or [rho] : 17 h. 20 m. + 37° 14′ : 4-5·1 : 314·4° : 3·80″. 'Gem of a beautiful coronet' (Webb)."
Page 288: 'Lyrae' corrected to 'Lyræ'.
"Lyræ [epsilon], double double, 241, 242;"
Page 291: 'obsering' corrected to 'observing'.
"methods of observing, 65-67;"
Page 292: 'elongagations' corrected to 'elongations'.
"orbit and elongations, 89;"
Page 292: 'GUIDFORD' corrected to 'GUILDFORD'.
"BILLING AND SONS, LTD., PRINTERS, GUILDFORD."