POPl'LAR ASTRONOMY 



145 



about the sun. The result is that each 

 year when the earth's orbit and me- 

 teor's cross each other, which happens 

 about August 10, there is a display of 

 shooting" stars. 



Though they are called shooting 

 stars, every one knows that these 

 bodies are not the stars that are falling. 

 The fixed stars are at enormous dis- 

 tances away from us, and most of them 

 are millions of times bigger than our 

 earth. If millions of meteors reach the 

 earth every twenty-four hours, the 

 earth must be slowly getting heavier. 

 The increased weight would show its 

 effect on the earth by making it rotate 

 slower on its axis, and the day as a 

 result becoming longer. Since the first 

 recorded astronomical observation the 

 earth has not changed the length of its 

 day by as much as the one hundredth 

 part of a single second, and hence, w r e 

 must conclude that the average shoot- 

 ing star is very small, most of them not 

 weighing more than a single grain, 

 with an occasional one as big as an 

 apple or even paving brick. 



The earth's atmosphere is so dense 

 that a great amount of friction is caused 

 by the particle moving, and in its quick 

 flight the energy of motion is trans- 

 ferred to heat. The result is that the 

 small particle of matter becomes so 

 hot that it glows and becomes lumi- 

 nous. The meteor is generally con- 

 sumed during its short flight. Once in 

 a while the meteor is so large that it is 

 not all burnt up, and a portion of it, 

 fused on the surface, and scarred by 

 its flight, reaches the earth as a 

 meteorite. 



Photographs of meteors are often 

 obtained by the astronomer, generally 

 by accident, when one crosses the field 

 of the camera, while it is being exposed 

 for some other purpose. Very often 

 such photographs show a sudden 

 brightening, then a dimming of the 

 light, and a second brightening, as is 

 seen on a splendid photograph taken 

 by Professor Barnard showing a 

 nebula in the constellation of Cygnus 

 and a meteor trail. 



Evidently the meteors in passing 

 through the earth's atmosphere must 

 move in paths which are parallel to 



each other. However, as these parallel 

 lines are projected back to the back- 

 ground of the stars, their apparent 

 positions are changed. As perspective 

 makes the two tracks of a railroad 

 appear to meet in a point, so all the 

 paths in a meteoric shower appear to 

 radiate from a point in the sky. This 

 point is called the radiant, and the 

 shower takes its name from the con- 

 stellation in which the radiant is found. 

 The August shower has its radiant in 

 the constellation of Leyra. 



Amateurs may do very interesting 

 work by taking with them their sky 

 map and noting on them the paths of 

 the meteors. Locate them from their 

 position among the bright stars, note 

 the time, the brightness, the color: and 

 producing the paths backward they 

 should come together in a small area 

 not far from the bright star Vega. At 

 the same time a splendid opportunity 

 will be further afforded of becoming 

 better acquainted with the heavens, 

 and learning the names of the bright 

 stars and constellations. 



THE PLANETS FOR AUGUST. 



Mercury is an evening star, but is 

 uninteresting during August. Venus 

 as a morning star is drawing closer to 

 the sun. and rises but a short time be- 

 fore dawn. Mars has been in the even- 

 sky for a year, but sets less than an hour 

 aPer the sun, and is now very faint, 



To the amateur with a telescope, 

 Jup'ter is still very interesting. Its 

 surface shows a remarkable amount of 

 detail, and it is well worth watching. 

 It is at quadrature, or 90 from the sun 

 on July 29, and at the middle of the 

 month was on the meridian at 3 P. M. 

 Everybody recognizes it as the bright 

 evening star in the southwest. 



Saturn is becoming brighter each 

 day, its rings show well in a small tel- 

 escope. It is a morning star, and is on 

 the meridian at the fifteenth of the 

 month at 4.45 A. M. 



Uranus can be located from the posi- 

 tion as shown on the sky map. With 

 a good telescope one can recognize it 

 by its disk, differing thereby from a 

 star. It is on the meridian at the 

 middle o\ the month about 10 P. M. 



