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Transactions. 



sides of the Pole, give a check as to its direction, if the star map be turned 

 round so as to make the position of the Great Bear on it agree with its 

 position in the sky when you are looking north and leaning half back. 



Star Map No. 1 (looking North). 



Star Map No. 2 (looking South). 



1. Note that the diagram is made for 50° north latitude. 



2. Note that the time to be used is the local time of the place of 

 observation. 



3. Note that, owing to the daily rotation of the earth about its axis 

 and to its yearly revolution round the sun, the stars appear to have two 

 motions, the daily motion and the annual motion : i.e., — 



(a.) On any given day a star moves across the sky, parallel to the 

 Equator, at the rate of 15° an hour, from east to west ;* 



(6.) During the year, besides the daily motion, every star has an apparent 

 motion (parallel to the Equator) towards the west of about 30° 

 a month, or nearly 1° a day* ; that is, any star is in the meridian 

 (due south) about two hours earlier to-day than it was on the 

 same day last month, or nearly four minutes earlier to-day than 

 it was yesterday. 



4. During your voyage to the seat of war you should make yourself 

 familiar, by looking at the sky every clear evening, with the stars shown 

 on the diagram, especially with Aldebaran, Sirius, Regulus, Spica, Antares, 

 Altair, Markab, and perhaps a Arietis. 



A. First Method. — To find the south approximately for any day and 

 hour (local time). Follow the date-line diagonally up to the right until 

 you come to the horizontal hour-line ; the stars on or near the vertical line 

 through that point are on or near the meridian — i.e., due south or nearly 

 due south of you. Check this by the north as found by the Great Bear 

 (star map No. 1). 



Example on the 1st October, at 8 p.m. The south is somewhat to 

 the left or east of Altair ; at 11 p.m. on the same evening the south will 



* It does not follow that the bearing of a star — east or west, parallel to the horizon 

 — varies on account of (a) by 15° an hour, or on account of (6) by 1° a day. 



