SOME RECENT ASTRONOMICAL EVENTS. 



By C. G. AiJBOT. 



The yoar 1901 has been a icinaikaMo one in th(> liistory of astronomy 

 for the number of unportant r)l)servati()ns and discoveries which have 

 been recorded. I have selected for tlie following account six, perhaps, 

 the most interesting. These are (1) recent determinations of stellar 

 motion in the line of sight; (2) advances in astronomical photography; 

 (3) the measurement of the heat received from the stars; (4) the 

 observation of tlie plan(>t Eros; (5) the total solar eclipse of Ma}' 18, 

 li»ol. and ((>) the history of the new star in Perseus. 



1. UKCKNT DETERMINATIONS OF STELLAR :\IOTION IN THE LINE OF 



SIGHT. 



It is now over thirty years since Sir William Huggins made the 

 earliest application of Dopplers principle to the problem of determining 

 the velocity of motion of the stars in the line joining the star with the 

 observer, technically called the line of sight. Before this all measures 

 of stellar motion had been by the comparison of accurate positions 

 obtained man}' years apart, and giving thus the stars' " proper motion" 

 or motion at right angles to the line of sight. The principle of Dop- 

 pler. however, ofiers a means of discovering the other component of 

 stellar motion, for in accordance with it the apparent wave length of 

 light is increased or diminished by the recession or approach of the 

 source, just as a locomotive whistle becomes of higher pitch as it 

 comes toward us and lower as it goes away. It requires, then, in 

 theory, but the comparison of well recognized lines in the stellar 

 spectra with the corresponding ones in the spectrum of a terrestrial 

 source, to see whether or not the star lines are shifted toward the 

 blue or the red, together with a measurement of the amount of this 

 shifting to decide if the star is approaching or receding from us, and 

 at what rate. In practice, however, the displacements caused by 

 stellar motion are so slight that the effects of a varying temperature 

 of the apparatus and of other causes make this one of the most diffi- 

 cult lields of astronomical investigation. 



153 



