THE FACE OF THE SKY FOR DECEMBER. 



By A. C. D. CROMMELIN, B.A., D.Sc, F.R.A.S. 



Table 82. 



Date. 



Greenwich 

 Noon. 



Dec. i 



„ 6 



,, II 



„ i° 



, 21 



„ 26 



M 3* 



Sun. 

 R.A. Dec. 



h. in. o 



16 27"9 S.21'8 



1 6 49*6 22*5 



17 n'6 

 17 33'° 



17 55*8 



18 i8'o 



23*0 

 23*3 



23 '4 

 23*4 



18 40'2 S.23'I 



Moon. 

 R.A. De 



h. m. e 



19 38-6 S. 25*9 

 23 34*8 S. 2-4 

 3 19-9 N.2 3 -o 

 8 11*9 N.23'9 

 12 33-1 S. 5*6 

 17 14*7 S. 28*1 

 21 52*2 S. 15*0 



Mercury. 

 R.A. Dec. 



h. m. 

 15 24-2 



15 28-4 

 »S 44 '9 



16 8-5 



16 36'i 



17 *"3 



S. i6"o 

 16 '2 

 i7'5 

 •*9*3 

 21*0 

 22*5 



17 38*2 S.23'6 



Venus. 

 R.A. Dec. 



h. m. o 



15 T7'i S.i7'o 



15 42'5 i8'7 



16 8*4 20"2 



16 34*8 21*4 



17 1 "6 22*3 

 17 28 '7 23 "o 

 17 56*oS.23-4 



Mars. 

 R.A. De 



7 47'3N.2 3 -8 

 7 45 '3 24' t 



7 4- -8 

 7 36-8 

 7 3°'5 

 7 23*0 

 7 i4*6N.26"2 



24 '5 

 24-9 



25*3 



Jupiter. 

 R.A. Dec 



h. m. 



19 20M 

 19 24*6 

 19 29'! 

 19 33'8 

 19 38*6 

 9 43*4 



S.22'5 



22*4 

 22*2 



22 'O 

 21 '9 

 21*7 



19 48-3 S.2I*5 



Saturn. 

 R.A. Dec. 



h. m. a 



4 56*4 N.2o"g 

 4 54-6 20 *9 

 4 52 "9 20 "8 

 4 51*1 20*8 

 4 49*4 20'7 

 4 47*8 207 

 4 46'3 N.2o*7 



Neptune. 

 R.A. Dec. 



h. m. 



59*9 

 59 "6 

 59*2 

 58-7 

 58-2 

 57*7 



N.20'I 

 20 '2 

 20*2 

 20*2 

 20*2 

 20 "2 



N.20"3 



Table 83. 



P is the position angle of the North end of the body's axis measured eastward from the North Point of the disc. B, L 

 are the helio-(planeto-)graphical latitude and longitude of the centre of the disc. In the case of Mars, T is the time of 

 passage of Fastigium Aryn across the centre of the disc. In the case of Jupiter, L t refers to the equatorial zone; L 2 to 

 the temperate zones; T lt T 2 are the times of passage of the two zero meridians across the centre of the disc ; to find inter- 

 mediate passages apply multiples of 9 h 50£ m , 9 h 552 m respectively. 



The letters tn, e, stand for morning, evening. The day is taken as beginning at midnight. 



The asterisk indicates the day following that given in the date column. 



The Sun reaches its greatest South Declination (Winter 

 Solstice) December 22 d 10i h tn. Its semi-diameter increases 

 from 16' 15" to 16' 17-J". Sunrise changes from 7 h 46 m to 

 8 h 8 m ; sunset from 3 h 52 m to 3 h 58 m . 



Mercury is an evening star; reaches elongation, 21° W., 

 on 10th, H° N. of Venus, 2 d 8 h e. Semi-diameter diminishes 

 from 4" to 2£". Fraction of disc illuminated increases from 



k to a. 



Venus is a morning star, but getting too near the Sun 

 for convenient observation. Disc practically full. Semi- 

 diameter 5". 



The Moon.— First Quarter 5 d 2" 59 m e; Full 13 d 3" m e ; 

 Last Quarter 20 d 4 h 16 m e. New 27 d 2 h 59 m e. Apogee 

 6 d 11" e. Perigee 21 d 2 h e, semi-diameter 14' 48", 16' 10" 

 respectively. Maximum Librations, l d 6° W, 13 d 5° E, 

 13 d 6° S., 26 d 6° N, 28 d 5° W. The letters indicate the 

 region of the Moon's limb brought into view by libration. 

 E. W. are with reference to our sky, not as they would 

 appear to an observer on the Moon. (See Table 85.) 



Mars rapidly approaches opposition. Nearest Earth on 

 January 1st, distance 0-622. This is an unfavourable 

 opposition as regards distance, but favourable as regards 

 planet's declination. It will be seen that both hemispheres of 

 Mars are observable, but the Northern one is best placed. 

 The semi-diameter during December increases from 6l" to 7-J-". 

 The unilluminated lune is on the West: its width diminishes 

 from I" to 0. 



Jupiter is an evening star, but almost invisible. Polar 

 semi-diameter, 15i". 



Table 84. 



Configuration at 5 h e for an inverting telescope. 



Satellite phenomena visible at Greenwich, 2 d 6 h 27 m IV. Tr. 



I.j 3 d 4" 54 



ll d 4 h 15 m 

 14a 4*1 4411 



Sh. I. These are all in the evening hours. The reappearance 

 from eclipse takes place on the east of the disc, to the right in 

 an inverting telescope. 



436 



