* 279281] Parallax : Star Catalogues 363 



the most important is the great catalogue of 324,198 stars 

 in the northern hemisphere known as the Bonn Durch 

 musterung, published in 1859-62 by Bessel's pupil Friedrich 

 M'ilhelm August Arge lander (1799-1875); this was extended 

 (1875-85) so as to include 133,659 stars in a portion of 

 the southern hemisphere by Eduard Schonfeld (\$>2$>-\'&y\) ; 

 and more recently Dr. Gill has executed at the Cape 

 photographic observations of the remainder of the southern 

 hemisphere, the reduction to the form of a catalogue (the 

 first instalment of which was published in 1896) having 

 been performed by Professor Kapteyn of Groningen. The 

 star places determined in these catalogues do not profess 

 to be the most accurate attainable, and for many purposes 

 it is important 'to know with the utmost accuracy the 

 positions of a smaller number of stars. The greatest 

 undertaking of this kind, set on foot by the German 

 Astronomical Society in 1867, aims at the construction, by 

 the co-operation of a number of observatories, of catalogues 

 of about 130,000 of the stars contained in the " approximate " 

 catalogues of Argelander and Schonfeld ; nearly half of the 

 work has now been published. 



The greatest scheme for a survey of the sky yet attempted 

 is the photographic chart, together with a less extensive 

 catalogue to be based on it, the construction of which was 

 decided on at an international congress held at Paris 

 in 1887. The whole sky has been divided between 18 

 observatories in all parts of the world, from Helsingfors in 

 the north to Melbourne in the south, and each of these is 

 now taking photographs with virtually identical instruments. 

 It is estimated that the complete chart, which is intended 

 to include stars of the 14th magnitude,* will contain about 

 20,000,000 stars, 2,000,000 of which will be catalogued 

 also. 



281. One other great problem that of the distance of 

 the sun may conveniently be discussed under the head 

 of observational astronomy. 



The transits of Venus (chapter x., 202, 227) which 

 occurred in 1874 and 1882 were both extensively observed, 



* An average star of the I4th magnitude is 10,000 times fainter 

 than one of the 4th magnitude, \\hich again is about 150 times less 

 bright than Sirius. See 316. 



