DISTANCES 07 THE STAKS. 261 



The parallax of the finest double star of the 

 southern hemisphere (a Centauri) has been calculated at 

 0"-9128 by the observations of Henderson, at the Cape of 

 Good Hope, in 1832, and by those of Maclear, in 1839. w 

 According to this statement it is the nearest of all the fixed 

 stars that have yet been measured, being three times nearer 

 than 61 Cygni. 



The parallax of a. Lyrae has long been the object of 

 Struve's observations. The earlier observations (1836) gave 8 * 

 between 0"'07 and 0"-18; later ones gave 0"-2613, and a dis- 

 tance of 771400 mean distances of the earth, with a period 

 of twelve years for the transmission of its light. 24 But Peters 

 found the distance of this brilliant star to be much greater, 

 since he gives only 0"'103 as the parallax. This result con- 

 trasts with another star of the 1st magnitude (a, Centauri), 

 and one of the 6th (61 Cygni). 



The parallax of the Polar Star has been fixed by Peters at 

 0"'106, after many comparisons of observations made be- 

 tween the years 1818 and 1838 ; and this is the more satisfac- 

 tory, as the same comparisons give the aberration at 20" < 455. 25 



given by Bessel, 0"-3136, 0"-3483, and 0"'3744, this celebrated 

 double star has apparently come gradually nearer to us in 

 light passages amounting respectively to 10, 9^, and 8 T 7 ^- years. 



22 Sir John Herschel, Outlines, pp. 545 and 551. Madler 

 (A .$/;., s. 425) gives in the case of a Centauri, the paralla'x 

 0"-9213 instead of 0"' 9 128. 



** Struve, Stell. compos. Mens. microm., pp. clxix.-clxxii. 

 Airy makes the parallax of at Lyrae, which Peters had pre- 

 viously reduced to 0"*1 still lower, indeed too small to be 

 measureable by our present instruments. (Mem. of the Royal 

 Astr. Soc., vol. x. p. 270.) 



34 Struve, on the Micrometrical admeasurements by the 

 Ureat Refractor at Dorpat, (Oct. 1839,) in Schum., 

 Nachr.. no. 396, s. 178. 



* Peters, in Struve, Astr. stell., p. 100. 



