336 



THE GUIDE TO NATURE 



it until the next morning. It is pos- 

 sible that if the weather is favorable, 

 Mercury can be followed from elonga- 

 tion until this time, when the two ob- 

 jects will form a beautiful figure in the 

 northwestern sky. 



Venus reaches its greatest distance 

 west of the sun on April 20 when it 

 will rise three hours before sunrise. 

 Those who are up before dawn have 



3 at 7 hrs. 3 min., and to reappear from 

 eclipse at 10 hrs. 21 min., (Eastern 

 Standard Time). Similarly the third 

 satellite will begin to transit the plan- 

 et's disc at 10 hrs. o min., and the sec- 

 ond satellite on April 6 at 8 hrs. 52 min. 

 The second satellite will reappear from 

 eclipse on April 8 at 7 hrs. 41 min. ; the 

 third will disappear in eclipse on April 

 16 at 8 hrs. 12 min., and the first may 



"Figure 2. Showing the motion of two of Saturn's moons during the present month. The largest of 

 these is Titan, which is easily visible in a three inch telescope. If the satellites are observed on other 

 dates than those indicated, their positions can be estimated by bearing in mind that Titan performs one 

 revolution in IS days 23.3 hours and Rhea in 4 days 12.5 hours. The former will reach its greatest eastern 

 distance from Saturn on April 15, 9 hrs. 13 min. A. M. ; the latter will reach its greatest eastern elonga- 

 tion on April 5, 4 hrs. 18 min. P. M. 



doubtless noticed how very brightly it 

 has been shining in the southeastern 

 heavens. It will not again enter the 

 evening sky until November 24. 



Mars is slowly retrograding (or 

 moving westward), its motion carry- 

 ing it from Virgo across the borders 

 of Leo into the position shown in Fig- 

 ure 1. This retrograde motion will 

 cease on April 26 and the planet begin 

 to run rapidly eastward again, though 

 it will not have passed entirely through 

 the long constellation Virgo until next 

 September. It is still in excellent po- 

 sition for observation though its dis- 

 tance from us increases from sixty-four 

 to seventy-six millions of miles during 

 the month, and it will in this time lose 

 about two-thirds of its brightness, 

 though it will still be more than three 

 times as bright as a first magnitude 

 •star. 



Jupiter may still be seen in the early 

 •evening, though it is fast sinking in the 

 west. It has now arrived well to the 

 •east of a line joining the Hyades and 

 the Pleiades, and its eastward motion 

 -will for some time be accelerated. It 

 now sets so early that but few of the 

 phenomena of its satellites can be seen, 

 but the first satellite may be seen to 

 disappear behind the planet on April 



be seen to reappear from eclipse on 

 April 19 at 8 hrs. 40 min. These are 

 most interesting phenomena to watch 

 in a small telescope. 



Saturn is in excellent position for 

 observation in the eastern borders of 

 Cancer in the position shown in Figure 

 1. Figure 2 shows the path and posi- 

 tion of the largest moon, Titan, during 

 the present month ; this can be well 

 observed by the possessor of a small 

 telescope of perhaps three inches aper- 

 ture. This remarkable moon is much 

 larger than our own moon, being al- 

 most exactly as large as the third 

 moon of Jupiter and almost half as fat- 

 through as the earth. It occupies fif- 

 teen days twenty-three hours in pass- 

 ing once around the planet from which 

 it is about seven hundred and seventy- 

 one thousand miles distant. It is the 

 sixth in order of distance from the 

 planet, there being ten satellites alto- 

 gether, the most distant one being no 

 less than eight million miles away. The 

 extent of the system is thus enormous, 

 far greater than that of any of the 

 smallers worlds, though not so great 

 as that of Jupiter which has one satel- 

 lite nearly twice as distant as the outer- 

 most satellite of Saturn. 



