202 



THE GUIDE T< > NATURE 



Evening Sky Map for September. 



BY PROF. ALFRED MITCHELL OF COLUMBIA 



UNIVERSITY. 



Two important congresses of astron- 

 omers have just taken place which are 

 of interest to all who watch the skies. 

 The first was a meeting of the Astro- 

 nomical and Astrophysical Society of 

 America which met at Harvard Uni- 

 versity from August 17 to 19. Here 

 was presented the results of the latest 

 researches concerning the celestial 

 kingdom, the motion of the stars, the 

 activity of the sun, the distribution of 

 stars in space and the evolution of solar 

 systems. Chief among the papers were 

 those bearing on Halley's Comet. The 

 general consensus of opinion was that 

 the tail of the comet which appeared 

 in the east, when astronomers expected 

 it in the west, and whose appearance 

 caused so much perplexity at the time, 

 was not the main tail, but a smaller de- 

 tached portion. The photographic his- 

 tory of comets has shown many such 

 fragments which shoot off from the 

 main tail for no reason that is as yet 

 apparent. Professor Barnard's mag- 

 nificent picture showed a remarkable 

 secondary tail in the Brook's Comet of 

 1893 and similar features in the More- 

 house Comet of 1908. Undoubtedly, 

 on the night of May 19, Halley's 

 Comet had an existence somewhat sim- 

 ilar to that photographed by the Bruce 

 telescope on the evening of June 6. 



The meeting at Harvard was ren- 

 dered specially interesting by the pres- 

 ence of a score of European astrono- 

 mers who took part in these meetings, 

 and who then journeyed to California to 

 attend the second and more important 

 congress, that of the Solar Union 

 which met at the Carnegie Solar Ob- 

 servatory at Mt. Wilson, near Pasa- 



dena. This latter conference runs over 

 into the first week in September. The 

 problems discussed there relate only 

 to the sun, the most important body 

 in the universe to us. Magnificent 

 work has been done at the Mt. Wilson 

 Observatory by Professor Hale and his 

 corps of astronomers, and it is un- 

 doubtedly the greatest observatory in 

 the whole world devoted to solar re- 

 search. 



EQUINOCTIAL STORMS. 



The month of September brings in its 

 train the first touch of cool weather 

 and frost, and the so-called "equinoc- 

 tial storms." The sun "crosses the line" 

 on September 23, the autumnal 

 equinox, and summer is astronomically 

 at an end. The seasonal change of 

 weather generally brings about that 

 time a violent storm, with its attendant 

 disaster to shipping. As similar storms 

 occur in March, while the sun is near 

 the spring equinox, there has naturally, 

 down through the centuries, grown up 

 the impression that the sun's crossing 

 the equator is directly responsible for 

 these equinoctial storms. Nothing 

 more absurd could be imagined. The 

 equator in the sky is as imaginary a 

 circle as the equator on the earth. In 

 fact, the celestial equator is simply the 

 plane of terrestrial circle, produced out 

 to the heavenly sphere. One travelling 

 at sea never knows when he is crossing 

 the equator unless the navigator makes 

 astronomical observations for the pur- 

 pose, and in a similar way the time 

 that the sun is on the equator can be 

 found out only as the result of obser- 

 vation and calculation. 



Weather is not made on the spot, 

 but is the result of influences spread- 

 ing over large areas. Changes in the 

 moon and soots on the sun have been 



