91000,000,000 times the light of a star of magnitude I.
9,100,000,000,000 times the light of a star of magnitude 6.
The square roots of these numbers show the number of times we should increase the actual distance of the sun in order that it might shine as a star of the corresponding magnitude. Under these conditions the distance and paral lax of the sun would be: Sirius; Distance, 100,000: Parallax, 2'.06 Mag. 1; Distance, 302,000: Parallax, 0'.68 Mag. 6; Distance, 3,020,000: Parallax, 0'.07 From the large size of the parallaxes, it is evident that the sun must be a very small star in the heavens. But its nearness renders it a very important star, one in which we can study the second stage of stellar development in all its details.
Researches by means of radial velocity, proper motion and parallax determinations show the presence of groups of stars in the sky like the Taurus group, the Ursa Major group, etc., in which the stars are moving with motions that are equal and parallel. To the Ursa Major group belong all the stars of the ex cept the two extreme ones, and also such widely separated stars as Sirius, p Auriga: and a Corona. Such results show the necessity of co-operation among the different observatories in order that observational work may be done with the highest degree of accuracy. So far the weakest part of the measured values has been the parallax determinations. Recent work by means of photography with telescopes of great focal length has shown the possibility of greatly increasing the accuracy of parallax measures overthe results obtained visually.
Several American observatories possessing large telescopes, together with the Greenwich Observatory, are co-operating in parallax de terminations. The American observatories are: Allegheny, Dearborn, McCormick, Mount Wil son, Swarthmore, Van Vleck and Yerkes.
The position of the apex of the solar motion is fixed by Weersma from the proper motions of 3,600 stars at right ascension 268° and dec lination, 31°, north, and by Boss from 5,400 proper motions deduced from his 'Preliminary General Catalogue,' at right ascension 271° and declination 34°, north. Campbell, from the investigations of the spectra of 1,047 stars, places the position at right ascension 272° and declination 27°, north. The motion of the solar system through space was found by Campbell to be 17.85 kilometres, or about 12 miles per second. This speed carries the solar system 255,000,000 miles per year, or 3.75 times the earth's mean distance from. the sun.
Twentieth century astronomy will have as its special study more detailed information con cerning the motions of the stars and their dis tances in order that more complete knowledge may be gained regarding stellar evolution, and regarding the shape and size of the universe, and the distribution and motions of the heavenly bodies forming it.
The best books on the subject are Kayser's 'Handbuch der Spectro scopie> (6 vols.) ; Scheiners'
Spectroscopie (Frost's translation) ; Camp bell's
Motions' and Newcomb-Engel mann's