DISCOVERY OF SATELLITES OF AlARS. 407 



ASTRONOMY. 



DISCOVERY OF SATELLITES OF MARS. 



Professor Asaph Hall, of the Washington Observatory, has recentl}^ an- 

 nounced the interesting discovery of two satellites attendant upon the planet 

 Mars. At about eleven o'clock on the night of August 16, Professor Hall, 

 by the aid of the great 26 -inch refractory telescope, noticed a very small 

 star following Mars by a few seconds. Two hours later he looked again and 

 to his surprise found that the distance between planet and star had not 

 increased, although the former was moving at the rate of fifteen seconds per 

 hour. Hardly crediting his discovery, Mr. Hall delayed further observation 

 until he could bring the matter before his colleague, Professor jSTewcomb, 

 and that astronomer, being confident that the discovery of a satellite had 

 been made, calculated roughly its time of revolution, which he found to be 

 one day and eight hours. This enabled the prediction of the probable place 

 on the following night — a prediction which was verified. On the morning 

 of August 17 another satellite appeared, and its identity Avas fully recognized. 



The distance of the first satellite from the planet is between 15,000 and 

 16,000 miles, w^hich is less than that of any other known satellite from its 

 primary, and only about one-sixteenth the distance of the moon from the 

 earth. It is exceedingly small, having a diameter of not over 100 miles. 

 The inner satellite is believed to be still closer to the planet, and to have a 

 period of less than eight hours. The first moon is distant eighty, the second 

 thirty seconds from their primary. Further and more accurate details will, 

 however, soon be forthcoming, as probably the keen eyes of astronomers the 

 world over will now be turned upon Mars. Next to our moon, more full 

 and accurate knowledge is possessed regarding Mars than of any other 

 heavenly body. Yenus is nearer to the earth, but when most closely ap- 

 proximated she is invisible, being concealed by the solar light. Mars, 

 however, may be examined under favorable circumstances, and during the 

 present year the conditions are especially advantageous, owing to the planet 

 being in opposition to the sun, near j^erihelion. The apparent disk is now 

 larger in the proportion of three to one than when the planet is in aphelion, 

 while the illumination is more brilliant in the proportion of three to two. 

 At the same time the planet is nearer perihelion than previously for more 

 than thirty years ; so that in the heavens its brightness is but little inferior 

 to Jupiter. 



While the surface of Mars has been mapped with remarkable accuracy, 

 and although probably no other planet has been subjected to more keen and 

 continuous scrutiny, yet up to the present time all searches for satellites 

 attendant upon it have been fruitless. Most astronomers have not hesitated 



