POPULAR ASTRONOMY. 



i33 



The closest possible approach of the 

 two planets takes place when earth is 

 at A, and Mars at B ; this distance is 

 evidently (128,500,000 — 93,000,000) , 

 353.-2 millions of miles. In 1909 the 

 distance is 38^2 millions. 



The earth goes about the sun in a 

 year of 36554 days. Mars travels 

 slower and takes 687 clays. If the sun, 



the earth every two years and fifty 

 days. A look at the small diagram 

 will show after a favorable opposition 

 takes place, that Mars is farther off 

 at each successive opposition till the 

 time of the least favorable approach 

 happens, when the distance is 154,- 

 500,000 — 93,000,000, or 6iy 2 million 

 miles. Favorable oppositions re-occur 



Evening SkyMap for JULY 



JULY MOON PHASES. 

 FIRST QUARTER. JULY 25 

 FULL MOON. JULY 3 

 LAST QUARTER. JULY 10 

 NEW AAOON. JULY 17. 



imf 



Columb' a 

 Uniircrsiy 



FACE SOUTH AND 

 HOLD THL MAP OVER 

 YOUR HEAD -THE TOP 

 NORTH. AND YOU WILL SEE 

 THE STARS AND PLANETS 

 JU5T AS THEY APPEAR 

 INTHEH£AVEN3 



SOUTH 



earth and Mars are in a straight line, 

 with planet and sun on opposite sides 

 of the earth, Mars is said to be in op- 

 position, opposite the sun, and conse- 

 quently comes on the meridian at mid- 

 night. As earth moves quicker about 

 the sun, it takes it some time to gain 

 a lap in the celestial course, and it is 

 but an elementary exercise in arith- 

 metic to show that the time required 

 is 780 days. This is the synodic pe- 

 riod, the time from opposition to op- 

 position. Thus Mars will be close to 



after seven synodic revolutions or 

 once every fifteen years, and the most 

 favorable oppositions are those which 

 happen about the middle of August. 

 In 1907, opposition occurred in July, 

 in 1909 in September, so that neither 

 are so well situated as those of 1892 

 and 1877. But the opposition of the 

 present year is more favorable than 

 that of 1907, first, because Mars is a 

 little closer, and second, because it has 

 a greater declination, and so is high- 

 er up towards the zenith and better 



