ASTRONOMICAL NOTES

Evening Star, Issue 22147, 30 September 1935, Page 13

ASTRONOMICAL NOTES

THE SKIES 111 OCTOBER [Written by A. G. C. Ckust, M.Sc., for the ‘ Evening Star.’J POSITION OF THE STARS Local sidereal time, 24b; latitude. 46dcg S.

Tlie 'stars will occupy the following positions four minutes earlier each evening, as at midnight, October 2-3, 11 p.m. on October 17, and 10 p.m. on November 2:— Due south shines the Southern Cross, its brightest star. Alpha Crncis, being IScleg above the horizon. Alpha Centauri is S.S.W., 21dog. An tares, in the Scorpion, S.W. by \V., 4deg, Altair W.N.W., 12deg, and Fomalhaut N.W., 70deg. In the eastern sky the bright constellations of the summer sky begin to appear. Aldebarafi is E.N.E., 2deg, Rigel E., 14deg.. Sirius E.S.E.. sdeg, Canopus S.E., 33deg, and Achernar, now the highest. of, our bright stars, S.E., 72deg. The Moon will pass the bright planet Jupiter on the forenoon of October 2, while the afternoon of the 3rd will find her close to Antaros, and on the same evening she will pass 2deg south of Mars. Early on the 6tb first quarter will occur, and at 11.40 p.m. on the 7th, our satellite will be placed W.N.W., 40deg. On the evening of the 9th the Moon will pass Gcleg north of the ringed planet Saturn, and on the forenoon of the 10th. 27deg north of Fomalhaut, full moon occurring on the afternoon of October 12. At 11.20 p.nn the same evening the Moon will be N.E. by' N. 53deg. On the forenoon of October 16 the Moon will pa.>s north of Aldebaran, last quarter will occur on the afternoon of the 19th, and a conjunction with Venus early on the 24th. The Moon will pass .Mercury on the 2Gth, new Moon falls on the evening of . October 27, the Moon will again pass Jupiter early on the 30th, and Antares the same evening. The planet Mercury will be stationary in the evening sky on October 6, in inform! conjunction with the Sun on the 18th. and stationary in the morning sky on Octobeh 26. The planet Venus is now a brilliant object in the morning sky, her greatest brilliancy being attained on October 15. On the afternoon of the 35th she will pass 2.6 deg south of the faint and distant planet, Neptune. The planet Mars is visible throughout the moiith at 24h S.T., his position in the sky changing from S.W. by W., 4deg, to W. by S., 21dcg. About Oetober°l6 he will pass within O.Sdeg of the third magnitude star, Theta Ophictichi. The planet Jupiter is no longer visible rt 24h S.T., but will still be visible in the early evening' sky. . The. planet Saturn. at 241 i S.T., will be placed N.W., .Sldeg, 'during the month.'' His prominent satellite. Titan, will be ni west'elongation on the forenoons of October 3 and 19. From the Queen’s Gardens, Dunedin, at 24h S.T., Antares will appear .very' low, and Mars very low to rather low, over High street, Fomalhaut very high over Burlington street, and Achernar very high in the opposite direction, while Pigel is low over the Early Settlers’ Hall. CONSTELLATIONS OF THE SOUTH CIRCUMPOLAR ZONE II.: CENTAURUS, THE CENTAUR.. ) -—i — • This brilliant cousteilation, representing a centaur, a creature of Greek mythology possessing the head, trunk, mid arms of a man, with the body and legs of a horse, lies partly in the south circumpolar zone, and, as the two ‘‘ pointers ” to the Southern Cross belong to it, it ii convenient to describe it now. Like Orion and Crux, Centaurus contains two stars of the first"-magnitude. In the zone square 31,72 may be mapped Beta Centauri, of mag. 0.86 and type 81, a bright blue star 160 light years' distant and one thousand times'as bright as the sun. It has a spectroscopic companion, and the temperature and diameter of its primary are probably 40,000 deg absolute, and 4.2 times the width of the Sun. respectively. In the zone square 27,69 conies the magnificent binary, Alpha Centann, the nearest stellar system to the Earth, whose light takes four years and fifteen weeks to travel to onr eyes. Its combined magnitude is 0.06, but a small telescope shows it to be a double star. The primary is of m»R. 0.33, the secondary 1.70, and the pafr revolve around their common centre of gravity in a broad oval curve, their average distance apart being 22 times that from Die Earth to the Sun, while the time taken to/ complete one revolution is 80 years. The bright star is white in colour and 17 per cent, brighter than onr Sun, but the companion is yellow apd yields ofily one-third sufipower. According to New Zealand measurements, the temperature of the primary is 6,320 deg, and its diameter O. of that of the Sun, or 790,000 miles, while the secondary is at a temperature of 3,900 deg, with a diameter 1.9 times that of the Sun, or 1,640,000 miles. . As this implies an apparent diameter of 0.0135 second of arc, it should be measurable with an interferometer in the Southern Hemisphere. Accompanying this beautiful binary system in its journey through space is a faint star of the eleventh magnitude, one of the faintest stars known to exist. In the south circumpolar portion of Centaurus there is one_ star of the second magnitude. This is Gamma, in the square 39.87, of magnitude —4 and type AO, distant 302 light years. At present' a powerful telescope is necessary to reveal the fact that tins is a binary system, for it consists of two equal stars of mag. 3.1. these take 203 years to revolve, aroumi their common centre of gravity, and their mean distance apart is 63 times the distance from‘the Earth to the »nn. The surface temperature of the pair is 12 OOOdeg absolute, and their, diameters are 2.3 times that of the Sun, while their sunpowers are each 52. This region of the sky contains four stars of-the third magnitude. Lambda, of mag. 3.3 and type 89, occupies the zone square 49.73, on the preceding or west side of the Southern Cross. Lambda Centauri is an 87 snnpower star distant 150 light years, 2.5 times as wide as the Sun. with temperature of 14.OOOdeg. Delta, of mag._ 2.9 and type B3p, in the square 45.85, is 180 light years distant, and yields 190 times the light of the Sun. It is 2.8 times as wide ns the Sun, and its temperature is 19.500 deg. A spectroscopic companion is suspected. In the square 31.80 we map Epsilon, of magi 2.6 and type 81, whose light takes two and a-half centuries to travel to onr eyes, and whose snnpower is 520. Its surface temperature is 21.600 deg, . end it is 4.4 times as wide as the Snu. A most interesting star is the intensely Mue one, Zetn. in the square 26.84.' The spectroscope shows the

presence of two spectra of unequal intensity, due to twd stars which revolve in the short period of only 8.0 days, at a distance apart of only 16.000,000 miles. The light from Zeta Cehtnur-i takes 380 years to reach us, and is almost as blue as that of Delta Orionis, the magnitude being 3.1 and the type B2p. The suupmvers of the two stars forming the system must be about 360 and 160, and if they are each 2.3 times as' wide as 'the Sun, the brightfer oiie must have the astonishingly high temperature of 80,000 deg absolute, while tho fainter one is at 23,000 deg. In Cejitaurns, south of 45deg. the colours of six fourth magnitude stars have been measured. 3* ho, in the square 41.84, is of mag. 4.2 and type 88, 230 light years array and 100 times as bright as the Kmi. with a surface temperature of 27,100 deg and diameter 1.7 times that of the Sun. Sigma, ol the same magnitude and type, in the Kono square 42.86, is 250 light years distant ami yields 120 suupower. It is twice as wide as the Sun, and its surface temperature is 23,200 deg. In tho square 40.87 is Tail, of mag. 4.0 and type A2, distant 155 light years and fifty times as bright, as the Sun, a bine star with a surface temperature of 13,900 deg and a. diameter 1.9 times that of the" Sun. Similar in colour is Xi 2, of mag. 4.4 and type 83, in the square 35.85. Tins is a double-lined spectroscopic binary 300 light years away, which we may picture os a pair of stars, one 1.9 times as widp as the Sun and 83 times as bright, and Mue in colour, with a temperature of 18,400 deg; the other 3,3 times as wide as the Sun and 48 times as bright, a pale bine star with a temperature of B,7oodeg. These stars are only 13,000.000 miles apart—i.e., oneseveuth. of the distance from the Earth to the Sun, and they revolve in a period of 7.6 days. A companion star of the ninth magnitude, and therefore actually about as bright as our Sun, accompanies them in their journey through spacb, at a distance not less than 2,200 times the distance from the Earth to the Sun. TJpsilon 2 Centanri may be mapped in the square - 24.85, its mag. being 4.4 and its type E 5. It has a spectroscopic companion and is 330 light years distant, yielding 100 suupower. The larger star of the pair has a probable temperature ojr 5,500c10g, and is 15 times as wide as the Sun. 'The magnificent globular cluster Omega Centanri occupies the Square 31.86. It contains nearly 6,400 stars, and is distant 22,000 light years, whence each star in it yields over 100 suupower. Tho colour indicates their average temperature as ll.OOOdeg, and diameter 2.8 times that of the Sun. Tile stars described outline the lower or “ horse ” part of tho Centaur. The name is frequently contracted to “ Cen.”