474 



KNOWLEDGE. 



December, 1911. 



occurs on Jan. 14. His diameter diniinislie.s from IJV' to 10". 

 Veiling of surface details by mist or cloud in the Martian 

 atmosphere seems to have occurred in several regions of the 

 planet in October, according to MM. .Antoniadi. Jarry- 

 Desloges. and others. 



Ceres, the largest of the asteroids, is in a %ery favourable 

 opposition in January, being in high north declination, and 

 also near perihelion. Its diameter is 4J() miles, just I of the 

 Moon's, and it will be of the 7th magnitude, and thus easily 

 visible in the smallest telescope or binocular; a map of 

 surrounding stars is given, which should make it easy to pick 

 the object up and follow its motion from day to day. The 

 brightest stars in the map are of mag. 5h, the faintest of 

 mag. 9i. Faint stars are onl\- shown when fairly near the 

 planet's track. 



Jupiter is a morning star, and just beginning to become 

 observable after conjunction with the Sun. Its Equatorial 

 Diameter increases from 32" to 34" ; the Polar is 2" less. The 

 defect of illumination on the West limb is 1". The configura- 

 tions of the satellites as seen with an inverting telescope at 

 6'' in are : — 



The following phenomena are visible at Greenwich : — 

 1" 5" M)"' in. I. Oc. R. : 2" 6" 14™ ni. IIL Tr. E. : /" 7" 24'" ;;;. 

 I. Sh. I.: S" 7"40""«;, I. Oc. K. : 9'' a*" 23'" ,n. III. Sh. I. • 

 7" ]'" ;«. II. Oc. R. : 7" 12" ;«, III. Sh. K. ; 15" 6" 34™ 52^" ni. 

 I. i:c. D. ; 16" 4''40'" ;;;, I. Tr. I.: 5" 21'" 1 ■)",„, II. Ec. D. ; 



5" 58'" m, I. Sh. E. : 0" 53'" ;);. I. Tr. E. ; 18" 4" 37'" in II.. 

 Tr. E.; 20" 5" 14'" in. 111. < )c. R. ; Zj'^ 5" 3S'" ni, I. Sh. I.; 

 6" 38'" I. Tr. I. ; 7" 51"' ;/;. I. Sh. E. : 24" 6'' S'^m, I. Oc. R. ; 

 25"4''44'" ;». II. Tr. I.: 5" 18'" ;». II. Sh. E. ; 7" 23'" /)(. II. 

 Tr. E. : 27" 5" S™ 5'' w. III. ICc. R. ; 7" 35"' m. III. Oc. D.; 

 30J 7" 31™ „,. I. Sh. I.; 31" 4" 50™ 17' in, I. Ec. D. The 

 eclipses take place high left of the disc in an inverting telescope, 

 considering the direction of the belts as horizontal. 



S.\TURN is still well placed for observation. Its equatorial 

 diameter is 19". major axis of ring 44", minor axis 15". The 

 shadow of the ball on the ring is visible on the East side. 

 The satellites except the outer ones, lapetus and Phoebe, are 

 in almost the same plane as the ring, so their apparent orbits 

 are widely open ellipses. The times of some Eastern Elonga- 

 tions are given ; intermediate ones are foimd by applying 

 multiples of l" 21" for Tethvs, 2" 18" for Dione, 4" 12.1"' for 

 Rhea. 



Tethvs, 2" 6" c : 8" lO" in ; 14" 2" in : 19" f>" c : 25" lo" ;/; ; 

 31" 2" ;;/. Dione 2" 3" c ; 8" 2" ni ; 13" 2" c ; 19" l" in: 

 24" noon ; 29" ll" e. Rhea 5" lO" in ; 14" ll" ;;; : 23" noon ; 

 Feb. 1" noon. For Titan and lapetus, E.W. stand for E. and 

 \\'. elongations, I.S. for inferior and superior conjunctions. 

 Titan 5" 6" /;; W. 9" 4" in S, 13" 8" /;;. E, 17" 9" in I., 21" 5" //; 

 \V, 25" 3" in S, 29" 7" /;/ E. lapetus, Jan. lO" 9" c I. 

 peb. 5' 8 ' in W. This satellite is much easier to see W. 

 than E. of the planet : it is presumed to rotate in the same 

 time as its revolution. 



Uranus is in\isible. being in conjunction with the Sun on 

 January 20th. 



Neptune is very favourably placed, being in opposition on 

 January 13th. It is of the 8th magnitude. 2:{" in diameter. .\ 

 map is given of the stars near its path. Their magnitude 

 ranges from 6.J to 9.1. With its aid a powerful binocular or a 

 li-in. telescope should find the planet. In December, it is 

 7i" south of Pollux. Its satellite. Triton, is too faint to justify 

 the inclusion of an cphemeris here. 



Comets. — The numerous comets visible in England in the 

 autumn have now passed to the south, and become much 

 fainter. Ephemerides are given for the use of southern 

 observers ; that of Brooks's comet is due to Dr. Smart. 



It is hoped that Ouenisset's Comet will be observed as 

 long as possible in the Southern Hemisphere, as its orbit 

 resembles that of 1790 III. and its identitx- appears possible. 



(Continued on page 476.) 



