622 



KNOWLEDGE & SCIENTIFIC NEWS. 



[December, 1906. 



The Face of the Sky 

 for December. 



By W. Shackleto.v, F R.A.S 



The Sun. — O.i the ist the Sun rises at 7.45 and sets at 

 3.53; on the 31st he rises at 8.9 and sets at 3.58. The 

 equation of time on the 25th is only 7 seconds, and for 

 ordinary purposes is neghgible. 



Winter commences on the 22nd, when the Sun enters 

 the sign of Capricorn at 6 p.m. Sun spots have lately 

 been comparatively scarce ; at the time of writing two 

 small groups are visible on the solar disc. 



The positions of the Sun's axis and of the centre of 

 the disc are given below : — 



The Moon : — 



OccuLTATioNS. — The following table gives particulars 

 of the principal occultations visible at Greenwich before 

 midnight : — 



The Planets. — Mercury (Dec. i, R.A. 16" 15™; 

 Dec. S. 19° 46' ; Dec. 31, R.A. 17'' i9"> ; Dec. S. 22° 37') 

 was in conjunction with the Sun on the 30th of last 

 month, and is, therefore out of range during the early 

 part of this month. The planet is at its greatest westerly 

 elongation of 21"' 35' on the iSth, when he is a morning 

 star in Scorpio, rising nearly 2 hours before the Sun. 



Venus (Dec. i, R.A. 16'' 17""; Dec. S. 22° 26'; 

 Dec. 31, R.A. 16'' 2"'; Dec. S. 16° 20') is a morning 

 star in Scorpio rising about 6 a.m. near the middle of 

 the month. On the 31st the planet rises at 4.48 am., 

 or nearly 3J hours in advance of the Sun, on this date, 

 the telescope appearance is a very thin crescent, o-o8 of 

 the disc being illuminated. 



Mars (Dec. i, R.A. 13'' 16"; Dec. S. 6- 47'; Dec. 31, 

 R.A. 14'' 26"; Dec. S. 13" 21') is a morning star, in 

 Virgo and Libra. Near the middle of the month the 

 planet rises about 3 a.m. ; the apparent diameter of the 



disc is only 4"*6, which is too small for useful obser- 

 vation with telescopes of moderate power. 



Jupiter (Dec. i, R.A. G'' 41™ ; Dec. N. 22" 58' ; Dec. 31, 

 K.A. 6h 24™ ; Dec. N. 23° 14') is a brilliant object in 

 the evening, looking east; towards the end of the month 

 he is due south at midnight, being in opposition to the 

 Sun on the 28th. The planet is describing a retrograde 

 path in Gemini, about 8' north of the star 7 Geminorum. 



The planet is very favourably situated for observation 

 before midnight, and forms with his belt-like markings 

 and bright moons a most interesting object even in very 

 small telescopes. 



On the evening of the 30th, the moon will appear near 

 the planet. 



The equatorial diameter of the planet on the 15th is 

 47 "'5' whilst the polar diameter is 3"'i smaller. 



Saturn (Dec. i, R.A. 22'' 44™; Dec. S. 10" 10'; 

 Dec. 31, R.A. 22'! 50™ ; Dec. S. 9^ 27'), is situated about 

 2" south of the star r Aquarii. The planet is due south 

 about sunset, and well placed for observation during the 

 early part of the evening ; near the middle of the month 

 he sets about 10.30 p.m. The ring, which can be seen 

 in small telescopes with moderate powers, appears slightly 

 open as we are looking at an angle of 6", on the northern 

 surface. 



On the 5th, the outer major and minor axes of the 

 ring are respectively 39""9 and 4"-3, whilst the polar dia- 

 meter of the globe is i5"'8. The Moon will appear in 

 proximity to the planet on the evening of the 20th. 



Uranus (Dec. 15, R.A. 18'' 34™ ; Dec. S. 23° 32'), 

 is in conjunction with the Sun on the 31st, and hence is 

 unobservable. 



Neptune (Dec. 15, R.A. 6^ 51"'; Dec. N. 21° 2') rises 

 about 5.30 p.m. near the middle of the month, and is due 

 south about i a.m. The planet is situated in Gemini, 

 about ih^ N.W.of f Geminorum, but in small telescopes 

 without setting circles it is difficult to identify from the 

 numerous small stars in the same field of view, but he 

 can be detected by his motion if observations are made 

 on several successive nights. The planet is in opposi- 

 tion to the Sun on the 31st. 



Meteors : — 



The principal shower of meteors during the month is 

 the Geminids, Dec. loth to 12th; the radiant is near 

 Castor, in R.A. \'II'> 12™, Dec. + 33"^. The meteors 

 are short and quick, and difficult to record accurately. 



V.\riable Stars: — 



Minima of Algol may be observed on the 5th at 11. 17 

 p.m., the 8th at 8.6 p.m., the nth at 4.55 p.m., the 28th 

 at 9.48 p.m., and the 31st at 6.37 p.m. 



Ceti (Mira) is due at a maximum on the 20th, but 

 observations should be made some weeks on either side 

 of this date as the period is uncertain. 



Telescopic Objects: — 



Double Stars: — i Pegasi 2i'' i7'5"', N. 19° 20', mags. 

 4-5, 8-5 ; separation 36"-2. 



7r Andromeda: o"^ Si'S". N. 33" 11', mag. 4-0, 8'0 ; 

 separation 35"'3. 



a Piscium I'l sB-g™, N. 2° 17', mags. 3-7, 47 ; separa- 

 tion 3"-6. 



1 Trianguli 2'' 6-6"', N. 29°5o' ; mags. 5, 6-4 ; separa- 

 tion, 3"-5. 



Clusters : — ( ^ vi. 33, 34). The Perseus clusters visible 

 to naked eye and situated about midway between 7 Persei 

 and Cassiopeia:. These magnificent clusters are de- 

 scribed by Smyth as "affording together one of the most 

 brilliant telescopic objects in the heavens." 



(M. 34.) A mass of small stars about the 8th magni- 

 tude ; not very compact. The cluster is just perceptible 

 to the naked eye about 5° N.W. of Algol. 



