38 



ASTRONOMICAL PROGRESS IN 1902. 



It would be natural to suppose that the 

 brighter stars were the nearer and their proper 

 motions the greater, but this seems not to be the 

 case, or at least it often fails. The most rapid 

 proper motion in the sky is that of two stars 

 invisible to the naked eye. Groombridge 1830, a 

 star of the sixth magnitude, has long been called 

 the runaway star. It has a proper motion 

 amounting to 7" a year, which would carry it 

 around the sky in one hundred and eighty-five 

 thousand years. Its velocity is thought to be 

 200 miles a second. The latest and most rapid 

 known is that of an eighth-magnitude star 

 in the southern sky. Its proper motion is 

 8" a year, or sufficient to carry it across a space 

 apparently hidden by the diameter of the moon 

 in two hundred and fifty years, or, in miles, 

 round the earth in eighty-three seconds. The 

 latest record of Groombridge 1830 is from the 

 Lick Observatory Bulletin, No. 4, which gives 

 the proper motion of the star as 7.05" a 

 year, which with Newcomb's adopted parallax 

 of 0.14", would denote a velocity perpendicular 

 to the line of sight of 150 miles a second. The 

 Bulletin gives the radial velocity (in line of 

 sight) as 59 miles a second. The above-men- 

 tioned parallax of the star gives its distance as 

 23J light years. The same Bulletin confirms the 

 variability of Delta Orionis in the line of sight, 

 discovered by M. Deslandres at Meudon. The 

 results from three photographs are -f- 3 kilome- 

 ters a second, +51, and 69. A large variation 

 has been discovered in the radial velocity of 

 Omicron Persei. The range of variation in this 

 star and in Eta Orionis are. the largest yet dis- 

 covered among spectroscopic binaries with one 

 dark component. The well-known Algol varia- 

 ble Delta Librae exhibits a considerable varia- 

 tion in the line of sight, proving that it is a 

 double star, which never has been seen with a 

 component. Ten spectrographs of the dog-star 

 were obtained between December, 1901, and 

 March, 1902, which give for the epoch 1902.06 a 

 radial velocity of. 6.57 kilometers a second. 

 This value, combined with others previously 

 made, gives its parallax as 0.21", making his dis- 

 tance in light years nearly twice as great as was 

 formerly supposed. 



Binary Stars. Recently 300 binary systems 

 have been discovered. This work is still progress- 

 ing, and many astronomers are engaged in it. 

 The sky is covered with them, but they were 

 never suspected until the invention of the spec- 

 troscope and the application of photography. 



Binary stars are divided into three classes: 1. 

 Telescopic, where both components are visible. 

 2. Spectroscopic, where only one is seen, the other 

 being too close to be visible in any telescope, 

 but both being bright and each giving a spec- 

 trum. 3. This class of binary stars, unlike those 

 of No. 2, give but one spectrum, one component 

 being incapable of giving a spectrum. Stars of 

 No. 1 type are both seen with the telescope to 

 revolve round each other, but always in a plane 

 perpendicular, or nearly so, to the line of sight. 

 The 'spectral lines of the approaching star will 

 all be slightly moved toward the violet end of 

 the spectrum, and those from the receding star 

 toward the red, thus causing the lines of hydro- 

 gen, sodium, helium, iron, etc., from each star 

 to be periodically single, broad, and double, and 

 rice rcr*fi. '\Vhen there is no to-and-fro motion 

 the linp are single. The behavior of stars of the 

 third class is quite unlike those of No. 2. If the 

 star gives but a single spectrum, it is either a 

 single star or a binary with one component dark. 

 If it is single its spectral lines will never move 



or be double, but if it is a binary the lines will 

 be seen to vibrate periodically toward the red 

 and the violet. The dark sun revolving round 

 the bright one periodically sways the bright one 

 to and fro by its attraction. 



If the reader will turn back a few lines and re- 

 read what is said about the radial motions of 

 Delta Orionis, Omicron Persei, Eta Orionis, and 

 Delta Librae, he will be able to comprehend how 

 the periodic motions of stars to and from the 

 Earth is ascertained. The following is a list of a 

 few recently discovered stars moving in the line 

 of sight: 



The discovery of radial motion in the trinary 

 system of the pole-star excites the admiration of 

 all who are able to appreciate its significance. 

 Prof. W. W. Campbell, director of Lick Observa- 

 tory, has, from observation secured since 1899, 

 shown that the velocity of the center of mass 

 of the binary has varied from 11.8 kilometers 

 a second in 1899 to about 13.5 kilometers a sec- 

 ond at the present time. It varied from 18.0 

 a second in 1896 to 11.8 a second in 1899. 

 A reversal has therefore taken place. The period 

 of the binary system 3 d 23 h 14.3m deduced in 1899 

 satisfies recent observations. 



The pole-star has a companion visible through 

 small telescopes, and was formerly considered a 

 telescopic binary. Lately the spectroscope has 

 determined the faint telescopic component to be a 

 spectroscopic binary with a period of about fif- 

 teen years. 



Much interest attaches to Mizar, which is a 

 telescopic binary and a spectroscopic trinary. 

 It is the middle star in the handle of the Great 

 Dipper. From observations made in March and 

 April, 1901, Vogel has deduced the relative mo- 

 tion in the line of sight. It is the brighter com- 

 ponent that is a spectroscopic double. Its spec- 

 troscopic duplicity was discovered by Prof. E. C. 

 Pickering. Prof. Campbell estimates that one 

 star in every five or six is a spectroscopic binary, 

 yet up to the present time not more than 40 are 

 known. 



Five Algol stars viz., V Puppis, X Carinae, 

 RR Centauri, Beta Lyra, and U Pegasi revolve 

 with their components in contact. 



Nebulae. Since Sir William Herschel's day 

 many thousand nebulae have been discovered. 

 They are now searched for by photography, 

 which by long exposure reveals what no visual 

 telescope can. At the Paris Observatory 23 new 

 ones have recently been discovered, and many at 

 the Cape Observatory and at the Arequipa sta- 

 tion of Harvard College Observatory in Peru, 

 and a great many have been discovered that es- 

 caped the eye of Sir John Herschel and others. 

 One of those discovered at the Cape was by one 

 hour's exposure depicted on a photograph plate. 

 In fact, it is a double, consisting of two spindle- 

 shaped nebulae side by side, but touching each 

 oilier in one place only. This was previously 

 discovered at Arequipa. 



