134 



THE GUIDE TO NATURE 



greatest faintness are roughly as fol- 

 lows : September 24, i A. M. ; Septem- 

 ber 26, 10 P. M., and September 29, 

 7 P. M. 



The Planets in September. 

 Mercury may be detected low in the 

 twilight glow throughout almost the 

 whole of the present month. On Sep- 

 tember I it sets almost exactly due 

 west, about one hour after sunset, while 

 on September ly it reaches its greatest 



and a little below the planet Mars. It 

 rises far in the northeast about four 

 and one-half hours before sunrise on 

 September i. and this time is increased 

 five and one-half hours by Sep- 

 tember 30. The reader who chooses 

 to observe during the early morning 

 hours will find that both of these plan- 

 ets are excellently situated for study, 

 while at this time he will also see the 

 brilliant Jupiter low in the southwest. 



Fig. 2. Measuring the distances of the stars. As the earth moves around its orbit, .ABC, a 

 near-by star seems to move about a similar orbit. ARCE 



elongation, by which time, however, it 

 will have moved much farther toward 

 the south point of the horizon. 



Venus passes the sun on September 

 12 and enters the evening sky, but 

 throughout the month it is far too near 

 the sun to be satisfactorily observed. 



Mars is daily becoming more con- 

 spicuous in the eastern heavens before 

 sunrise. On September i it rises four 

 and one-half hours before the sun, and 

 its own eastward motion among the 

 stars is so rapid that this time is in- 

 creased only to five hours by the end 

 of the month. This planet is now near 

 the summer solstice and so rises as 

 high in the heavens as does the sun in 

 mid-summer. It is approaching the 

 earth, its distance diminishing from 

 163,000,000 to 147,000,000 of miles dur- 

 ing September, and its brightness is 

 consequently steadily increasing. It will 

 be seen shining as a reddish, first mag- 

 nitude star. 



Jupiter will at once attract attention 

 in the southeast, just below the Great 

 Square of Pegasus. This world is now 

 slowly retrograding among the stars 

 and moving slowly downward and 

 westward from the Vernal Eqinox at 

 V, Figure i. The most numerous phe- 

 nomena of Jupiter's satellites will be 

 seen to occur on the evenings and 

 nights of September 2, 7, 14, 23, 25, 

 and 30. 



Saturn is in the morning sky, lying, 

 on September i, six degrees to the east 



The morning skies are thus far more 

 brilliant at present than those of the 

 early evening. 



The moon, which passed over the 

 bright star Antares, at E, Figure i, on 

 the i8th of last month will again occult 

 this object on September 15 at 3 A. M., 

 and in the course of its regular jovirney 

 around the heavens it will again hide 

 this star from view on October 12. But, 

 unfortunately, these interesting occul- 

 tations can only be seen by observers 

 who are near or below the equator of 

 the earth. 



The sun will pass the Autumnal 

 Equinox on September 23 at 10 hours 

 24 minutes 12 seconds P. M. (Eastern 

 standard time,) and at this instant 

 autumn will begin. It should also be 

 noticed that we are now drawing near 

 to the time of a sun-spot maximum. 

 The observer who examines the sun's 

 disc will therefore almost surely notice 

 several spots upon its surface, and the 

 probability is that a few" of these inter- 

 esting objects will be seen which are 

 of an unusually large size. 

 Measuring the Distances of the Stars. 

 When the great astronomer Coper- 

 nicus, more than 350 vears ago, an- 

 nounced his discovery that the earth is 

 not fixed but that it is moving around 

 the sun, this new and startling idea 

 was opposed even by scientists, on the 

 strictly logical ground that such a mo- 

 tion of the earth must certainly cause 

 an apparent displacement of the stars 



