PARALLAX OF THE FAINT PROPER MOTION STAR 



NEAR ALPHA OF CENTAURUS. (PRELIMINARY 



ANNOUNCEMENT.) 



Bv R. T. A. Innes, F.R.A.S.. F.R.S.E. 



The discovery with the bhnk-microscope of a star of the 

 loth magnitude (1900, R.A., I2h. 22m. 55s., Dec, 62° 15'. 2) with 

 a large proper motion was announced in Circular No. 30 of the 

 Union Observatory. As this faint star is moving across the 

 sky in much the same direction and with much the same angular 

 motion as a Centaurus, it was at once guessed that its distance 

 from the sun would also be of the same order, which means 

 that it would be one of the nearest stars to our system. 



The first determination of its proper motion and the proper 

 motion of a Centaurus compared as follows: 



Faint Star 4^.9 towards 289° 



a Centaurus 3.68 ., 281 



but this first determination was not very secure, and the sugges- 

 tion that its proper motion was identical with that of a Cen- 

 taurus was hazarded. 



Observations to determine its parallax were started at the 

 Union Observatory by myself, and at the Cape Observatory by 

 Mr. Voute. My series will not be completed until the end of 

 August. Nevertheless, a weak and incomplete determination 

 may be of interest. So far, the Johannesburg observations yield 

 a proper motion of 3".9 a year, and a parallax of o".8o. It will 

 be seen that the proper motion is practically equal to that of 

 a Centaurus, whilst its parallax is somewhat larger (a Centaurus 

 o".75. Gill). Within the limits of error there is the chance 

 that the parallaxes are also identical. In any case the accordance 

 in both proper motion and parallax is sufficient to allow us to 

 say that the faint star is a member of the a Centaurus system, 

 and that it is perhaps the nearest star to our system. 



In astronomical units (the mean distance of the Earth from 

 the sun) this star is roughly about 6,000 units distant from a Cen- 

 taurus and 250,000 units from the sun. Its light-emission is 

 of the order of 1/10,000 that of the .sun. 



(Read, July 3, 1917.) 



