THE FACE OF THE SKY FOR JANUARY, 1912. 



By A. C. D. CRO^rMRLI^^ r>.A.. D.Sc, F.R.A.S. 



The foUowiiii; table gives the Kii;ht Ascension and Declination 

 of the Sun, Moon and Planets at iiiter\als of 5 days, at 

 Greenwich noon. 



The following table gives for the Sun, Mars and Jupiter: — 

 P the Position .\ngle of the Sun's or Pl.anet's North Pole, 

 measured from the North Point of the disc towards the ICast, 



The Sun is nearest to the earth on Jan. i. distance 

 'Jlj million miles; it is commencing its northward march, 

 slowly at first, but with increasing speed. At Greenwich it rises 

 at 8.8 on Jan. 1, sets at 3.58; it rises at 7.44 on Jan. 31. sets at 

 4.43. Its semi-diameter diminishes during the month from 

 Id' is" to Hi' 15". The minimum of simspot activity is 



Tahle 1. 



B the Hcliographical or Planetographical latitude of the 

 centre of the disc, and L the Heliographical or Planetographical 

 longitude of the centre of the disc, which in the case of the 

 Sun or Jupiter is reckoned from an arbitrarily chosen zero 

 meridian, in the case of Mars from the marking Fastigium 

 Aryn (formerly called Dawes Forked Bay). That of Jupiter, 

 system II, originally coincided with the great Red Spot. Two 

 values are given for Jupiter : I corresponds to the equator. II to 

 temperate zones. T the time of transit of the zero meridian 

 is also given for each of the given dates. Here and elsewhere 

 in these pages the time used is Greenwich Civil Time, day 

 beginning at midnight, and the letters in (morning), f (evening) 

 are used as abbreviations for a.m. and p.m. The quantities 

 P, B, are also gi\en for S.-iturn, and serve to indicate the 

 position of the minor axis of the ring, and the amount of its 

 opening. The additional quantities O. q, given for Mars are 

 the Position Angle (from North Point towards Fast) and the 

 amount, in seconds of arc, of the greatest defect of illmnination. 



expected in 1912 or 1913, but cannot as yet be predicted with 

 mathematical accur.acv. 



The Moon is Full, Jan. 4. l"30"'f.; L.n.. Ian. 11. 7" 43"' ;)j.. 

 New, Jan. 19, ll'' 10" /;;.; F.O.. Jan. 27, S" 51'" in.: Perigee; 

 Jan. 4. 2'' e., distance 221.400 miles (an unusually close 

 approach) ; .Apogee, Jan. 18, 2" in., distance 264,600 miles. 



The following gives the dates of the Moon's maximum 

 librations: Dec. 29, S° £.; Jan. 5, 6° S.; Jan. 10, 8° W.; Jan. 

 19, '-■ N.; Jan. 26, 7° E.; Feb. 1, 7' S. The letters E. \V. 

 indicate that the region brought into view is on the E^ast (Mare 

 Humorum side), or West (Mare Crisium side) respectively. 

 The letters N. S. indicate that the regions brought into view* 

 are at the Moon's N. or S. Poles. Observers will do well to 

 watch their libration opportunities to improve our knowledge 

 of the regions near the limb. 



The occultations visible at Greenwich are given on page 475. 



Mercury is a morning star. It reaches W. elongation 



Table 2. 



The 



■alues of T, T,, for Jupiter on intermediate 



days may be found by applyin.L; 

 respectively. 



multiples of 9" 505". 9" 



It should be mentioned that L is reckoned in the opposite 

 direction on the Sun from that used on Mars and Jupiter. 

 This difference is unfortunate, but it has become established 

 and cannot now* be altered. 



The two systems may be best explained thus: in that 

 used for the Sun the longitudes of Bombax* and New York 

 from Greenwich would be 73', 286" respectively ; in that used 

 for Mars and Jupiter the same tw*o longitudes w*ould be 

 Bombay 287°, New York 74°. 



(24° from Sun). Jan. 15. It is 6° N. of Moon, Jan. 17. h'" in. 

 Its diameter diminishes during month from 9" to 5"; the 

 illuminated part of disc increases from i to §. 



Vl-.NUS is a morning star, pretty well placed for observation. 

 It is 6° N. of Moon, Jan. 15, 5*" e. Its diameter diminishes 

 from IS" to 15"; the illuminated part of disc increases from 

 S to t 



Mars has passed opposition, but is still w*ell pl.*iced for 

 observation. The vernal equinox of the Northern Hemisphere 



473 



