ASTRONOMICAL PHENOMENA AND PROGRESS. 



servatories of the Eastern Continent. From 

 observations made on Sept. 2, 5, and 7, Prof. 

 F. Holetschek has calculated the following ele- 

 ments of Brooks' s comet : 



Time of perihelion passage, 1885, Aug. 9 7302, Berlin mean 



Distance from node to perihelion = 41 2V 54'' 



Longitude of node = 204 60 b9 



Inclination = "" "" " 



Longitude of perihelion distance = 9-87497 



THE PERIODIC COMETS. 



Minor Planets. In view of the large number 

 of these bodies already known, and the vast 

 amount of labor involved in the computation 

 of their ephemerides, astronomers begin to 

 look upon the discovery of new ones with dis- 

 favor. The following table shows the number 

 discovered during the current year : 



No. 244 has been given the name Sita. Of 

 the entire group JEthra (No. 132) has the least 

 perihelion distance == 1-604, and Andromache 

 (No. 175) the greatest aphelion distance = 

 4*726, so that their orbits extend over a space 

 of 4-726 1-604 = 3-122 of the earth's mean 

 distance, or, in miles, =92,500,000 x 3-122 = 

 288,785,000 = the breadth of the asteroid zone, 

 which, comparatively speaking, nearly covers 

 the region between the perihelion point of Ju- 

 piter's orbit and the aphelion of the orbit of 

 Mars. Hilda (No. 153) has the longest period 

 = 7'86 years, and Medusa (No. 149) the shortest 

 = 3-11 years. 



Motion of Stars in Line of Sight. The direction 

 of the displacement of the lines in the spec- 

 trum of any heavenly body at once indicates 

 whether it be moving toward or from the 

 earth, and the amount of such displacement 

 marks its velocity. A displacement toward 

 the red end of the spectrum tells with unvary- 

 ing certainty that the earth and the object are 

 receding from each other, while, on the other 

 hand, if it move toward the violet end, it is 

 indicative of a motion of approach. The rapid 

 rotation of Jupiter on his axis, for instance, 

 causes one limb to approach the observer, 

 while .the opposite limb recedes. The diameter 



of the planet and his rotatory period being 

 known, it is easy to compute in miles the ve- 

 locity with which the two limbs severally ap- 

 proach and recede. These displacements of 

 the lines in direction are used as bases of com- 

 parison when observing the changes of the 

 lines in the stars for determination of motion 

 in the line of sight, or, in other words, whether 

 moving toward or from us. This factor is in- 

 dicated by the spectroscope ; the telescope in- 

 dicates lateral motion only. 



For several years Sirius has been the sub- 

 ject of spectroscopic study by several astrono- 

 mers, notably by Dr. Huggins, who, in 1868, 

 called attention to the fact that the F line in 

 Sirius was displaced toward the red end of the 

 spectrum, and that it was receding from the 

 earth at the rate of about twenty-nine miles 

 a second. A few years later, by the same pro- 

 cess, it was ascertained that this rate was di- 

 minishing, until, in 1881, its recession equaled 

 only two miles a second, and soon thereaf- 

 ter ceased altogether. Shortly after the cessa- 

 tion of recessive motion, it became apparent 

 that the star was approaching the earth, at 

 first very slowly, but increasing in rapidity 

 until, at the present, it has an approximate 

 motion of about twenty-five miles a second. 

 This singular truth, which, so far as known, is 

 indeed unique, has given rise to a considerable 

 controversy among astronomers. The most 

 reasonable supposition as to its cause is that it 

 is revolving round the center of the system, 

 the star being both a double and a binary, 

 and, as is well known, the brightest star in 

 the heavens the Dog Star of the Egyptians. 

 The irregularities of the motion of Sirius (not 

 in the line of sight) led to the prediction of a 

 companion star, which, in 1862, was discov- 

 ered by Alvan G. Clark. It will be of interest 

 to note how these movements in the line of 

 sight will throw light on the orbital motion of 

 its companion. The following table shows the 



