THE STARRY HEAVENS FOR MAY 



407 



How We Find How Fast the Stars Are 

 Moving. 



When a star is moving toward us all 

 the lines of the color strip are displaced 

 toward its violet end ; if the star is mov- 

 ing' away from us all of its lines are 

 displaced slightly toward the red. And 

 the faster the star is moving the greater 

 this displacement will be. in fact, by care- 

 fully measuring it we can tell very ex- 

 actly how rapidly the heavenly body is 

 either approaching or receding from us. 



Thus, Spica, for example, now our 

 conspicuous south star, at S, Figure 1, is 

 found to be approaching us on the whole 

 at the rate of nine and one-fifth miles 

 each second. But in this case a careful 

 watching of the spectrum lines would 

 show us that this bright star has a very 

 complicated motion beside its general 

 motion toward us. Sometimes the lines 

 would be seen strongly displaced toward 

 the red and sometimes toward the violet, 

 and in short, we would soon discover 

 from their behavior that Spica is revolv- 

 ing about a dark and invisible companion. 

 Its orbit is three millions of miles in ra- 

 dius and the speed of Spica in its orbit 

 is no less than fifty-six miles a second so 

 that it completes one revolution in about 

 four days. It is this orbital motion 

 which causes it to alternately approach 

 and recede from us and so displaces the 

 lines of its spectrum in what seems at 

 first so irregular a manner. 



The Planets in May. 



Mercury enters the evening sky on 

 May 1st and reaches its greatest distance 

 east of the sun on May 31st. On the 

 latter date it will set in the northwest one 

 hour and forty minutes after sunset. On 

 the evening of May 30th, Mercury and 

 Saturn may be seen near together in the 

 sky, the former planet oassing to the east 

 of the latter on the forenoon of the next 

 daw At this time Mercury will be north 

 of Saturn at a distance from it equal to 

 five times the apparent diameter of the 

 full moon. 



Venus, Mars. Jupiter and Uranus are 

 all morning stars. The first is rapidly 

 approaching the sun, rising but one hour 

 and eighteen minutes before sunrise on 

 May ist and steadily decreasing this in- 

 terval during the month. The last three 

 planets are withdrawing from the sun 

 and thus coming into more favorable po- 

 sitions. On May ist. Mars rises one 

 hour and twelve minutes before sunrise, 



Jupiter two hours before sunrise and 

 Uranus at a little before 2 A. M. 



Saturn will steadily sink in the eve- 

 ning sky during the month. Although it 

 does not set until ten hours and thirty 

 minutes P. M. on May ist its westward 

 motion causes it to become nearly lost in 

 the sun's rays by May 31st. As before 

 noted, it will have drawn so near the sun 

 that on the latter date it will pass Mer- 

 cury and can then only be seen low in the 

 northwest for one hour and forty min- 

 utes after sunset. 



The New Comet: A Correction. 



The early bulletins regarding this body 

 stated that it drew nearest the sun in Au- 

 gust ; no year was mentioned. In our 

 last month's article it was assumed that 

 it was the past August which was re- 

 ferred to ; it now appears that the least 

 distance will be reached during the next 

 August. (The diagram of the former 

 article is correct but the position of the 

 comet in its path is in error). 



Consequently this body is now ap- 

 proaching us and will, in fact, be nearest 

 the earth in June, when it will appear 

 one hundred and sixty-five times as 

 bright as at the time of discovery. It 

 may thus become a conspicuous naked 

 eye object, but very unfortunately it will 

 then be so far below the celestial equator 

 that it cannot be seen from northern 

 latitudes. 



The Amateur in Astronomy. 



BY W. F. DENNING, F. R. A. S. 



It has been recently hinted that in 

 view of modern developments the ama- 

 teur is practically out of the field — or 

 soon will be — in astronomical work and 

 investigations. Present-day require- 

 ments are such that large instruments, 

 elaborate apparatus, and refined re- 

 searches, with perhaps spectroscopic 

 and photographic agenda, are abso- 

 lutely needed ; and often enough, the 

 necessary studies are most laborious, re- 

 quiring close application over a long 

 period, and including critical mathema- 

 tical analysis. These and other reasons 

 may be suggested for the opinion that 

 the' amateur is losing ground, and will 

 not take the prominent part he has done 

 in the past in aiding the progress of 

 astronomy. 



Judging, however, from the facts and 

 the teaching of recent years, such an 



