ASTRONOMICAL NOTES

Evening Star, Issue 22456, 29 September 1936, Page 13

ASTRONOMICAL NOTES

THE SHIES IK OCTOBER 1 1 [Written for the ‘ Star ’ by A. G. C. i Ckxtst, M.Sc.] L j POSITION OF THE STARS. Local sidereal time 24hrs, latitude i 46deg S. ' The following star positions hold good : locally at midnight October 2-3, 11.00 . p.m. on October 17, and 10.00 p.m. on ■ November 1, being in the same' posi- , tions four minutes earlier each even- ■ big. . i Due south shines Alpha Crueis, IBdeg ■ above the horizon, while Alpha Cen- : tauri is placed S.S.W., 21deg, and : Antares, in the Scorpion, S.W. by W., ; 4deg. Altair is now W.N.W., 12deg, and Fomalhaut N.W., 70deg. I In the east the bright stars of sum' ; raer are beginning to appear, Aldebaran being E.N.E., 2deg., Rigel E., i 14deg, and Sirius E.S.E., sdeg. In the ; S.E. shines Canopus, at an altitude of 33deg, and Achernar, now the highest of 'our bright stars, at 72deg. .Full Moon occurs on the. morning of October 1, the Moon’s position at 12 midnight on October 2-3 being N.E. hy. , N., 23deg. On the afternoon of October 5 the Moon will pass Aldebaran, and last quarter occurs at midnight October 7-8. Oil the afternoons of the 12th and 14th the Moon will pass tho Slanets Mars and Mercury, and New toon occurs on tho evening of tho 15th. Having entered the evening sky, the Moon will pass 2deg south of Venus on the afternoon of the 18th, and orily _ o.6deg south of Jupiter on the evening of the 20th. This should bo a very pretty conjunction. The Moon’s position at 10.40 p.m. on October 22 is W., 28deg., first quarter falls at midnight October 23-24, and on the morning of the 27th the Moon passes 28deg north of Fomalhaut. The same afternoon she passes Bdeg north of Saturn, and her position at 10.20 p.m. will he N. by W., 41deg. Full Moon will occur for tho second time in October on the afternoon of the 30th. The planet Mercury will be in inferior conjunction with the Sun on October 1, stationary in the morning sky on the 9th, and at greatest elongation west, 18deg, on the 16th. The planet Venus is now a brilliant object in the early evening sky, her position at 24h S.T. at the end of the month being S.W. by W., 3deg. The planet Mars, in the morning sky, will he in conjunction with Neptune on the morning of the 26th. The remote planet will be found o.4deg south of Mars, The planet Jupiter will he situated W.S.W., Bdeg to 12deg, during the month, at 24h S.T. The superior conjunctions of his four bright satellites occur as follow: —lo, first, October 2:01:05, seventeenth, October 30:09:01; Europa, first, October 4 :01:40; eighth October 28 ;23 :20; Ganymede, first October 2:18:16, fifth, October 31:11:27: and Callisto, October 14:21:32 and 31:17 ;25. The greatest elongation west of Ganymede will occur on Thursdays, greatest elongation east on Sundays. Callisto will be at west elongation on October 10 and 27, east on October 2 and 19.

The planet Saturn will be played N.N.W., 50deg to 51deg, at 24h S.T., during the month. His largest satellite, Titan, will be at west elongation on the afternoons of October 4 and 20, and at east elongation on the forenoons of October 12 and 28. From tho Queen’s Gardens, Dunedin, at 24h, S.T., Airfares will appear very low over High street, Fomalhaut very high ov<jsr Burlington street, and Aehernar very high in the opposite direction. At the same time Saturn will be rather high over Burlington street, and towards the end of the month Venus will appear _ very low over High street. Rigel, in Orion, will appear low to the right of the Early Settlers’ Hall.

CONSTELLATIONS OF THE SOUTH CIRCUMPOLAR ZONE. DORADO, PICTOR. AND RETICULUM. These three occupy a portion of the South Circumpolar Zone near Canopus. Like many of the modern constellations, they were originally given rather long names, which, however, make the meaning of the present names more intelligible. Dorado, indeed, needs no abbreviation, and appears to be of Spanish origin. Tho name means “The Swordfish.” Pictor was formerly called Equuleus Pictoris, the Painter’s Easel, so that, as it stands, it really means the Painter. Reticulum was originally Recticulum Rhomboidalis, the Rhomboidal Net. None of the stars in this region of tho sky are brighter than the third magnitude, and it seems scarcely necessary to look for the outline of the objects they are intended to represent as constellations.

Dorado contains one star, Alpha, of tho third magnitude. Its zone position is 78,32, and its colour is blue, indicating a temperature of 13,600 deg absolute. Its type is AOp and magnitude 3.5, but its distance is unknown. There are two stars of the fourth magnitude in Dorado, both of typo F 5. Gamma, of mag. 4.4, in the square 80.28, is 47 ligbc years distant and 3.5 times as bright as the Sun, which it exceeds in diameter by 15 per cent. Its pale blue colour indicates a temperature of. 7,620 deg. Beta Doradus is a very different type of star, its variation, which is of the Cepheid type, having been-discovered a few years ago by, a lady , amateur in Australia. Its zone position is 73,42, and it varies from mag. 4.2 to 5.6 in a period of 9.8 days. According to the Cepheid period-luminosity law this implies a change from 3,000 to 830 sun power and a distance of 760 light years. According to our colour measurements, which show a variation from white to yellow, the temperature at maximum _ is ,6,070 deg, and the diameter 52 times that of the Sun, while at minimum the temperature is 4,290 deg and the diameter 71 times that of the Sun. Before leaving this constellation wo must refer to the magnificent nebula, 30 Doradus, which forms a part of tho Great Magellan Cloud. It has been likened to a “ true lovers’ knot,” and also to an octopus, and it is indeed a fine object when viewed through a large telescope. Actually its size and brightness must bo prodigious when we recall that its distance is that of the cloud, about 100,000 light years. Tho zone position of this remarkable object is 66,44, Like Alpha Doradus, Alpha Pictoris is a third magnitude star of unknown

distance, its position being 73,50, mag. 3.3 and type A 5. It is a blue star of temperature 10,600 deg. Beta Pietoris, of mag. 3.9 and type A 3, may be mapped in the square 84,43. It is distant 58 light years, is pale blue in colour, with a temperature of ll,Boodeg, and 1.3 times as wide as the Sun, its sun power being 7.7. Gamma, in the square 79,44, of type KO and mag, 4.4, is 220 light years distant and 72 times as bright as the Sun. This yellow giant is 36 times as wide as the Sun, with a surface temperature of 3,670 deg. Reticulum contains one star of the third, magnitude also named Alpha Reticuli. and located in the square 70,33. It is of type G 5 and magnitude 3.4, and' its light takes 150 years to travel to our eyes. It is a star of 85 sun power, yellow in colour, with a diameter ,12 times that of the Sun. It has a_ companion of the 12th magnitude, distant 49 seconds of are. with-the same proper motion. In Reticulum there are also four stars of the fourth magnitude. Beta, in the square 66,31, is a yellow giant with a radial velocity that varies in a period of 1,912 days, its magnitude being 3.8 and type KO. It yields 62 sun power and is 140 light years distant. If it may be taken as a single star its temperautre is 4,350 deg and diameter 17 times that of the Sun. Delta, in the square 70,30, is a very remote star of type Ma and mag. 4.4. It is at least 800 light years away and 1,000 times as bright as the Sun, which it exceeds in diameter at least 200 times. It is orange in colour, its temperature being 3,290 deg. Probably similar,_ but of unknown distance and colour, is Gamma, of type Mb and mag. 4.5, in the square 69,32. Finely

Epsilon, of mag. 4.4 and type K2, in the square 73,32. is .93 light years distant and yields 13 sun power. Its pale yellow colour indicates a temperature of s,ooodeg and a ‘diameter 5.5 times that of the Sun. 'i'he three constellations described are not very conspicuous, but it will be ujied uiat our knowledge of them is still rather incomplete. ... The names take the genitive forms Doradus, Pictoris, and Heticuli, while the contracted forms are Dor., Pic., and Ret.