402 



THE GUIDE TO NATURE. 



The Heavens in April. 



BY PROF. ALFRED MITCHELL, OF COLUM- 

 BIA UNIVERSITY. 



The month of April will be the most 

 important in the history of Halley's 

 comet, and those who are interested in 

 astromony will now watch the skies 

 with redoubled interest. The comet 

 was discovered on September eleventh 

 last while still three hundred millions 

 of miles from the earth and sun, and 

 seven months of time before it should 

 swing' past the sun at its closest ap- 

 proach. When the comet was picked 

 up in the photograph of Max Wolf, it 

 was so faint that only the largest tele- 

 scopes in the world could find it, and 

 it showed not the slightest trace of tail. 

 During the past half year, the comet 

 has brightened far too slowly to suit 

 the average reader who has a fresh 

 wonder served up daily with his morn- 

 ing paper. However, during March it 

 has brightened enough to permit it to 

 be seen with a three inch glass, but it 

 did not have much of a tail, and was 

 rather disappointing. As far as we 

 know it has not become bright enough 

 to be visible with the naked eye, though 

 undoubtedly man)- thought they saw it. 

 During April all this will be changed 

 and the comet will undoubtedly blaze 

 forth in the skies. 



The diagrams show in a manner 

 readily understood by all the charac- 

 teristics of the comet's orbit. On April 

 20th the comet will be at perihelion, 

 when it comes within fifty-four and one 

 half million miles of the center of the 

 sun. Then it turns in its course and. 

 starts on its long flight for thirty-eight 

 years off into the depths of space to 

 a distance of three thousand millions 

 of miles. The closer and closer the 

 comet comes to the sun, the more does 

 the heat of the sun act on the material 

 forming the head, and generate forces 

 to throw off matter which eventually 



forms the tail. We are not absolutely 

 certain of the nature of the solid core 

 of the comet, though the consensus of 

 opinion seems to favor the idea that it 

 is made up of solid bodies some large, 

 some small, the whole being like a 

 great number of meteorites moving 

 along together. This lump which in 

 some comets is six thousand or eight 

 thousand miles in diameter, and in 

 smaller comets not more than one hun- 

 dred miles, is loosely packed together 

 with large interspaces. Science is 

 forced to this theory mainly on account 

 of the action of Biela's comet. 



This comet discovered in 1826 was a 

 most interesting one. Tt had a short 

 period of six and two third years, and 

 calculations showed that its path came 

 within twenty thousand miles of the 

 earth's. That was sufficient to start a 

 great comet scare— one of the many we 

 have had — that the comet was going to 

 collide with the earth, and as a result 

 the earth was to be blown to pieces. 

 This of course, proved that a "little 

 knowledge is a very dangerous thing." 

 for the calculations of the astronomer 

 showed that the earth would arrive at 

 the crucial point a month before the 

 comet. As we now know, no harm 

 came to the earth. 



HOW TO FIND THE COMET 



Meanwhile, the comet is rapidly in- 

 creasing in brightness. On February 

 3, Professor Barnard measured the 

 length of tail to be five million miles, 



