ASTRONOMY, PROGRESS OP, IN 1890. 



43 



including the belt and sword-handle. This im- 

 mense nebula is shown by three different expos- 

 ures, and is very distingtly marked." This ex- 

 traordinary photograph was made with a portrait 

 lens of 26 inches aperture and 8'6 inches focus, 

 with an exposure of three hours. 



Bright Lines in Stellar Spectra. As a 

 rule, the stars give spectra crossed by dark lines, 

 the same that our sun exhibits, but there are a 

 few exceptions. As spectroscopic investigation 

 is extended the number giving bright lines will 

 no doubt be largely increased. Following are a 

 few notable examples, mostly variables : Gamma 

 Cassiopeia, R Andromeda, Beta Lyras, 17 Cygni, 

 Eta Argus, R Hydra, Chi Cygni, Theta Muscae, 

 Phi Persei and Delta, and Mu Centauri. At the 

 Dun Echt Observatory, Scotland, 70 bright lines 

 were seen in the spectrum of 71 Cygni and 237 

 in that of Beta Lyras. The planetary nebulas 

 show by their spectra that they are closely allied 

 to stars with bright lines. 



Draper Memorial Fund. The fourth an- 

 nual report of the photographic study of stellar 

 spectra at Harvard College Observatory, by the 

 aid of the Henry Draper Memorial fund, deals 

 with subjects of absorbing interest to astrono- 

 mers. An expedition, directed by Messrs. S. J. 

 and M. H. Bailey, erected the Bache telescope 

 on a mountain 6,500 feet high in Peru, South 

 America. The weather, for the first six months, 

 was satisfactory, and about 1,300 photographs 

 were obtained of different portions of the sky 

 south of 25 of south declination, using expos- 

 ures of ten minutes. Two sets of plates were 

 taken, the center in one coinciding with the 

 corners of the other, thus causing every star to 

 appear on at least two plates. Excellent views 

 were obtained of the more remarkable southern 

 objects, as the nebula surrounding Eta Argus, 

 the trifid nebula, the cluster Omega Centauri, 

 X Doradus, and Kappa Crucis. At the begin- 

 ning of the rainy season the site was abandoned, 

 the work to be located elsewhere. Mrs. Draper 

 has provided another telescope for Harvard 

 College, replacing that sent to Peru, for the pho- 

 tographing of objects whose stellar spectra are 

 too faint to be studied with other instruments, 

 particularly those of the fourth type, although 

 the stars are red. The number of photographs 

 taken by the Bache telescope is 4,595 ; with the 

 Draper 11-inch, 2,510; with the Draper 8-inch, 

 713 ; and with the 15-inch, 65 ; making a total 

 of 7,883. 



Variable Stars. These bodies, as a rule, 

 give peculiar spectra, and occasionally one is 

 found whose variability has not been previously 

 known, but which yields a spectrum belonging 

 to one of the four types into which they are 

 classified. A recent examination of one of the 

 Harvard College negatives led to the discovery 

 that the Durchmusterung star + 48'2942 gives a 

 spectrum of bright lines resembling Omicron 

 Ceti and other long-period variables. Nova 

 Orionis, discovered in 1885 by Mr. Gore, now 

 known as U. Orionis, yields a bright-line spec- 

 trum, and is a variable of long period, changing 

 in l?3i days from 5 to 12-^ magnitude. Its 

 place is right ascension 5 h 48 m 17 s , declination 

 north, 20 9' 18". On March 26, 1890, Rev. T. 

 E. Espin observed bright lines in both Theta 1 

 and 2 Orionis. Great importance is attached to 



these observations by astronomers, for they in- 

 disputably prove that some of the so-called stars 

 are not stars at all, but nebulas greatly condensed, 

 which in future asons will arrive at the state of 

 ordinary stars or suns, when the lines in their 

 spectra will turn from bright to dark. Mr. Espin 

 publishes in " Astronomische Nachrichten," No. 

 2,963, a list of forty-three stars like those men- 

 tioned above. It is a continuation of former 

 lists, and begins with the tabular number 387. 

 The variable star discovered in 1888 by Prof. 

 Paul, of the Naval Observatory, Washington, 

 D. C., proves to be the shortest-period variable 

 yet discovered. It varies from 6 to 7'3 magni- 

 tude, going through all its changes, according to 

 Mr. Chandler, in the astonishingly short time of 

 3 h 20 m . The star's place for 1875-0 is right as- 

 cension 9 h 26 m 50% declination 28 4-7', and it 

 is known as 12 Antliae. 



Astro-Spectro Photography. One of the 

 most unexpected and wonderful disclosures of 

 the spectroscope and photography is the peri- 

 odic doubling of the lines in the spectra of Zeta 

 Ursas Majoris, Beta Auriga, b Ophiuchi, and 

 Alpha Virginis. In plates taken at Harvard 

 College Observatory on March 29, May 17, and 

 Aug. 27 and 28, 1889, the K line in Zeta Ursas 

 (Mizar, or the second from the end of the handle 

 of the Great Dipper) is clearly seen double. 

 Sometimes the line would appear distinctly 

 double, then unmistakably single, and, again, as 

 a hazy line. A close scrutiny of all the plates 

 showed that the line is double at intervals of fifty- 

 two days, beginning March 27, 1887, and that for 

 several days before and after these periods it is 

 hazy. This line of the star, being of less width 

 than the hydrogen lines, is better adapted for 

 the detection of duplicity. Through common 

 telescopes this star is an interesting double, but 

 the inference from this periodical duplication is 

 that it is triplex, the nearest component being 

 so close as to require for its discovery telescopic 

 magnification far beyond that which the capacity 

 of the most powerful glass will furnish, or the 

 atmosphere allow. The brothers Pickering are 

 of opinion that each component is equal to the 

 other in mass and intrinsic brightness, and that 

 the period of revolution is about one hundred 

 and four days. If the latter assumption is true, 

 the distance between their centers can not be 

 greatly more nor greatly less than that of the 

 planet Mercury from the sun. The distance be- 

 tween the components of Beta Auriga appears 

 much less, as it completes a revolution in four 

 days, the line being doubled every two days, cor- 

 responding to a distance between their centers 

 of only 8,000,000 miles, and an orbital velocity 

 of 150 miles a second. '* So enormous are their 

 motions," says Prof. Pickering, " that the change 

 in the spectrum is sometimes perceptible on 

 successive plates, and is very marked in the 

 course of an evening." 



Each star, say of Beta Auriga, gives a certain 

 number of lines, one being the K line, but if the 

 star be not in motion in the line of sight this K 

 line of each component star will be so close 

 as to be inseparable spectro-photographically, 

 though it might appear hazy; but if the plane 

 of their orbits be coincident, or nearly so, with 

 our line of sight, and, while revolving round the 

 center of gravity of the system, one shall be 



