Pope. — On the Southern Stars and other Celestial Objects, 



173 



a Centauri.—R. A. 14brs. 30mm. 47-07secs. Decl. 60° 17' 53-93". 

 Magnitudes, 1-2. The following table will give the position-angles, and the 

 distances of the components of this star, for selected epochs dm-ing the 

 forty-five years which have elapsed since 1834, when it was first accm-ately 

 measm*ed by the greatest of all astronomers, Sir J. Herschel : — 



Obseevee. 



Date. 



Position. 



Distance. 



Sir J. Herschel 



1834-7 





17-43" 



Sir J. Herschel 



1834-8 



218° 30' 







Sir J. Herschel 



1835-7 



219° 30' 







Sir J. Herschel 



1837-3 



220° 42' 







Sir J. Herschel 



1837-4 







16-12" 



Powell (from Webb) . . 



1864 



5° 7' 



7-85" 



Computed from mean places in F. M. G. C. 



1870-0 



17° 19' 



10-73" 



My recent measures . . 



1878-7 



156° 19' 



— 



My recent measures . . 



1879-75 



183° 8' 



4-55" 



With this table as a basis, it will be found that the major axis of the 

 apparent orbit hes nearly in the direction 26^° to 206^°, and that the 

 greatest elongation north is about 11", while the greatest elongation south 

 is 27". Mr. Powell makes the period between 76 and 77 years. If the 

 places of the two stars given by Lacaille (1750) were correct, however, the 

 period would be just about 85 years, for the angle of position computed from 

 his places of the stars is 218° 44', which a reference to the above table will 

 show, was very nearly Sir John Herschel's micrometrically- determined 

 position 84*79 years afterward. As, however, the distance obtained by Sir 

 John Herschel disagrees very materially with that deduced from Lacaille's 

 places of the stars, but Uttle weight is attached to the observation of 1750. 



This magnificent double star is the finest object of the kind in the 

 heavens. Besides being a bmary star of very short period, every one 

 knows that a Centauri is our nest neighbour among the stars, and that it 

 was the first to give up the secret of its parallax under du-ect Transit Circle 

 observations. The colour of this star is straw-yellow, or sometimes golden- 

 yellow, according to the state of the atmosphere. When there is haze, of 

 course the smaller star is somewhat more affected by it than the larger. This 

 tends to give it a slight brownish tint when the sky is not clear, a Centauri is 

 a star of the second class. Its spectrum is very like that of the sun. Even 

 the principal dark lines are fine, and they apparently occupy the same rela- 

 tive positions as do the well-known lettered lines in the solar spectrum. 



The resemblance between the two spectra is so striking that any one see- 

 ing the two spectra for the first time could hardly fail to notice the similarity. 

 More dispersive power, however, and the means of accurately determining 

 the position of the lines of a Centauri might show that they are not the 



