58 



KNOWLEDGE, 



[Makch, 1902. 



wbich to many eyes is ilistinctly visible witliout optical 

 oid. The famous Belgian astronomer, Houzeau, who 

 seems to have hail excolleut sijjht, saw the star k Tauri 

 double, and 51 and 56 Tauri separated, also t Orionis, and 

 others. 



Many of the stars are varialile in their light, and several 

 hundred of these curious and interesting objects are now 

 known to astronomers. In a few of these the light changes 

 may be followed with the naked eye. It is an interesting 

 question whetlur iiiiy of the lucid stars have disappeared 

 or changed in brightness since the early ages of astrono- 

 mical observations. Al-Sufi failed to find seven of Ptolemy's 

 stars, and Ulugh Beigh, comparing his observations with 

 the catalogues of Ptolemy and Al-Sufi, announced twelve 

 cases of su]iposed disappearance. Some of these may, 

 however, be due to errors of observation. Lloutanari, 

 writing in 1672, mentions two stars as having disappeared, 

 namely /3 and y of the constellation Argo, but these stars 

 are now visible in the positions originally assigned to 

 them. 



In a careful examination of Al-Sufi's description of the 

 stars written in the tenth century, and a comparison with 

 modern estimates and measures, I have found several very 

 interesting cases of apparent change in the brightness of 

 the lucid stars. Al-Sufi was an excellent and careful 

 observer, and as a rule his estimates agree well with 

 modern observations. We can therefore place considerable 

 reliance on his estimates of star magnitudes. " The Story 

 of Theta Eridani " has been well told by Dr. Andei'son in 

 Knowledge for July, 1893, and there seems to be no 

 doubt that this southern star, which is now only of the 

 third magnitude, was a bright star of the first magnitude 

 in Al-Suii's time ! The following are other interesting 

 cases of apparent change which I have met with in my 

 examination of Al-Sufi's work. The Pole Star was rated 

 third magnitude by both Ptolemy and Al-Sufi, but it is 

 now of the second magnitude, or a little less. The star 

 y Geminorum was rated third magnitude by Ptolemy and 

 Al-Sufi, or equal to S Geminorum, but y is now of the 

 second magnitude, and its great superiority in brightness 

 over I is noticeable at a glance. Another interesting case 

 is that of ? and c Persei, two stars which lie near each 

 other, about seven degrees north of the Pleiades. Al-Sufi 

 distinctly describes these stars as 6o//« of the 3 — 4 magni- 

 tude ; but Argelander, Heis, and the photometric measures 

 at Harvard agree in making ? about one magnitude 

 brighter than o. The stars being close are easily compared, 

 and their present great difference in brightness is very 

 noticeable. This is one of the most remarkable cases 1 

 have met with in Al-Sufi's work, and strongly suggests 

 variation in o, as ? is still about the same brightness as 

 Al-Sufi made it. The identity of the stars is beyond all 

 doubt, as Al-Sufi describes their positions very clearly, 

 and says there is no star between them and the Pleiades, 

 a remark which is quite correct for the naked eye. The 

 remarkable decrease in brightness of /3 Leonis (Denebola) 

 since Al-Sufi's time has been considered in my paper on 

 " Some Suspected Variable Stars " (Knowledge, August, 

 1899). That it was a bright star of the first magnitude 

 is fully- proved by the observations of Al-Sufi and Tycho 

 Brahe. These were careful and accurate observers, and 

 they could not have been mistaken about a star of the first 

 magnitude. /3 Leonis is now fainter than an average star 

 of the second magnitude, and there can be no reasonable 

 doubt that it has faded considerably since the tenth 

 century. 



There are some other discrepancies between Al-Sufi's 

 observations and modern estimates, but the above are 

 perhajis the most remarkable. With reference to lucid 

 stars not mentioned by Al-Sufi, he has not I think omitted 



any star brighter than the fourth magnitude in that 

 portion of the sky visible from his station. There are, 

 however, a number of stars between the fourth and sixth 

 magnitude which he does not mention. Of these the 

 brightest seem to be e Aquilae, p and \i. Cygni, and ? Coronae 

 Boreal is. 



With reference to the distribution of the lucid stars in 

 the sky there seems to be a well-marked tendency to con- 

 gregate on the Milky Way. It is a remarkable fact that 

 of the 15 brightest stars in the heavens, no less than 1 1 

 lie on or near the Milky Way, although the space covered 

 by the Galaxy does not exceed one-fifth or one-sixth of 

 the whole sky. From a careful enumeration of the stars 

 in or near the Milky Way which 1 made some years ago, 

 I found that of stars brighter than the fourth magnitude 

 there are 118 on the Milky \Vay out of a total of 392, or 

 about 30 per cent. From the Southern catalogue known 

 as the Urnnometria Aryentina, Colonel Markwick, f.r.a.s., 

 found 121 out of 228 stars to fourth magnitude, or a 

 percentage of 53 per cent. Ihese results seem to show 

 some intimate relation between the lucid stars and the 

 Galaxy. 



« 



ASTRONOMY WITHOUT A TELESCOPE. 



By E. Walter Maunder, f.r.a.s. 



XL— MORNING AND EVENLNG STAES. 



It is one of the necessary penalties of the modem tendency 

 towards city life that we are dissociated more and more 

 from that close intercourse with nature which was open 

 to our forefathers. How few of us ever care to watch 

 that great spectacle which was to them so full of wonder 

 and of awe, the silent, ceaseless procession of the starry 

 heavens ! It was not merely the sight of the thousand 

 flashing gems of the midnight sky that impressed them, 

 or their differences of colour and lustre, or the weird 

 manner in which they were distributed ; there was some- 

 thing more striking than all this, and that was their 

 ceaseless movement. There was the wonder ; that motion 

 was so stately, so regular, so unceasing. " Without rest, 

 without haste " they moved ; no star ever left its appointed 

 place in the celestial host, nor ever strayed from its 

 appointed path. It was a nightly miracle, a miracle both 

 of order and power. The thoughts to which it gave rise 

 lay at the root of many an ancient myth, and inspired 

 many a poetic outburst, chief amongst which stands the 

 grand 19th Psalm. Nor. though the secret of that regular 

 motion is understood to-day, is the sight of the movement 

 of the vast cosmical machine in the least less impressive 

 even now to any mind that can rise to some slight realisa- 

 tion of its true meaning. 



But the observers of those early ages had other thoughts 

 beside those of awe and wonder as they contemplated the 

 nightly march of the heavenly host ; there came a time 

 when they had familiarised themselves with the different 

 stellar groupings, and they saw that different constella- 

 tions ruled the night watches at different seasons of 

 the year. 



After a long night watch in which the stately march of 

 the heavenly host has been followed hour after hour, some 

 stars moving round the pole in narrow circles, others 

 passing out of view in the west, whilst new ones are ever 

 mounting upward from the under world in the east, there 

 comes a time when a change begins to be perceptible in 

 the latter quarter. Little by little the eastern sky begins 

 to brighten and the stars to pale, and now perchance it 

 may be that a star more magnificent than any that has 

 shone the long night through, comes upward, queen of 

 the night, as the night is coming to an end. As it rises 



