NUMEEE, DISTANCE, AND MAGNITUDE OF STAES. 



163 



The astronomer selected the star 61 Cygni as the one on which to perform his opera 

 tions. Several reasons influenced Bessel in the selection of this object. First, it is so 

 near the pole, that, with the exception of a small part of the year, it can always be 

 observed at night at a sufficient distance from the horizon. Second, it is a conspicuous 

 binary star, specially adapted by its double character to the instrument employed. Both 

 the constituents are yellow, but one smaller than the other has the deepest tint. Third, 

 the region occupied by 61 Cygni contains a number of minute stellar points close to it, 

 presenting admirable fixed points for measurement. Fourth, the star has long been 

 known to be distinguished by the great rapidity of its proper motion. In watching 

 this star, Bessel commonly took observations sixteen times every night whenever 

 opportunity offered. Without detailing the course he pursued, which would be uninterest 

 ing and unintelligible to most readers, it will be sufficient to state, that after a most 

 careful investigation, a variation in the apparent place of the star began to show itself, 

 increasing precisely as parallactic variation ought to increase, and diminishing as it ought 

 to diminish. The period of these changes was precisely a year ; and in all particulars 

 they corresponded exactly to the changes which ought to be produced by parallax. Still, 

 on account of their minute character, the observer hesitated to place dependence upon 

 them. But during another year of observation, the same results came out, and the 

 previous values were confirmed. This was the case also during a third year ; and all 

 doubt being now removed, Bessel announced to the world that he had compassed the 

 hitherto impassable gulf of space, and measured the distance to one of the fixed stars. 

 The final conclusion deduced, confirmed by the subsequent researches of M. Peters at the 

 Observatory of Pulkowa, assigns to 61 Cygni an annual parallax of 0"'349, rather more 

 than one-third of a second of space. This corresponds to the enormous distance of nearly 

 600,000 radii of the earth's orbit, or as many times 95,000,000 miles. The distance of 

 the star may therefore be set down in round numbers at sixty billions of miles. 



The mighty gulf which separates us from the stars having been once passed, the route 

 has been followed ; and succeeding observers have determined the parallax of a sufficient 

 number of stars to show that their results are entirely trustworthy. That of a Centauri, a 

 double star of the first magnitude, and one of the brightest sidereal objects in the southern 

 hemisphere, was next ascertained. This was effected by Professor Henderson, during his 

 residence as astronomer at the Observatory of the Cape of Good Hope. This star exhibits 

 the greatest amount of parallax hitherto observed ; and is consequently the nearest of any 

 yet examined. General dependence may be placed on the results given in the table : 



Stars. Parallax. 



1. a Centauri, . . 0"-913 



2. 61 Cygni, . . -348 



3. a Lyrse, . . -261 



4. Sirius, . . -230 



5. 1830. Groombridge, -226 



6. i Ursae, . .0-133 



7. Arcturus, . . 127 



Distance in Radii 



of the Earth's 



Orbit. 



225,920 



592,715 



790,287 



896,804 



912,677 



1,550,864 



1,624,134 



Distance in 



Billions of 



Miles. 



21 



56 



75 



84 



86 

 147 

 154 



Observers. 



Henderson. 



Bessel. 



Struve. 



Henderson. 



Peters. 



Peters. 



Peters. 



To aid the imagination in forming some idea of these distances, it may be stated, 

 that the conflagration of these stars would not be announced to us under periods varying 

 from upwards of three years to more than a quarter of a century, for a ray of light, which 

 darts to us from the sun in eight minutes, would require that time to travel through 

 the space between us and them. One delicate thread of a spider's web, placed before the 



