ASTRONOMICAL NOTES

Evening Star, Issue 21116, 31 May 1932, Page 3

ASTRONOMICAL NOTES

THE SKIES IK JUNE POSITIONS OF THE STARS [Written by A. G. O. Gkvst. At. Sc., tor the ‘ Evening Star.’] Local Sidereal Time, 14 Hours; Latitude 46deg S. The following positions hold good locally four minutes earlier each day, the above sidereal time being equivalent to 9.30 p.ra. on dune 2, 8.30 p.m. on Juno 17, and 7.30 p.m. on July Achenar is due south, elevation 14dog; Alpha Crucis, 18deg above the horizon, S.W. by S. ; and Canopus. 49deg higher up in the same direction. Itegulus is now N.W. by W.. 12deg; Spica, N.N.W., 54deg; Arcturus, N. 24deg; Antares, K.N.E. 56deg; and Alpha Centauri, now the highest bright star, S. by E. 75dcg. Alpha Centauri should bo especially interesting to Scotsmen, for it was the Scottish astronomer, Henderson, who first measured the distance of this, the nearest to the earth of all stellar systems. A faint star of the eleventh magnitude, 2.2dcg to tho south-west of Alpha Centauri, also belongs to the system, and is actually the nearest star yet discovered; hercc we shall refer to this faint star ns Proximo. The feeble light from Proxima takes four years and eight w.eH to reach our telescopes, and twelve weeks to reach the bright suns of Alpha Centauri. We recall that light and heat take Bmin 17sec to cross the ninety-three million miles of space from our sun to this earth, where their energy is so usefully employed, but Proxima is over fourteen thousand times as far as this from the central sun of its system. There are many stars in the heavens which appear to be keeping company with brighter ones at a very great distance, but this is perhaps the only case in which we have an exact knowledge of the distance between two members of a “ common proper motion ” system, as it is technically called.

Proxima, being so very faint, our knowledge of its physical properties is rather approximate. Certainly it is one of the tiniest of dwarf stars, giving only one ten-thousandth of the light of our own sun, and if, as is probable, it is of typo M (orange colour), its diameter •should he 'about forty thousand miles.

The bright stars of Alpha Centauri wo see by the light that left them four years sixteen weeks ago. If there was anybody living in tho vicinity who could pick up our wireless messages, the news of the outbreak of tho World War would reach them a fortnight after hostilities ceased, but the wireless waves passed Proxima six weeks before tho armistice.

Alpha Centauri is a magnificent example of a binary system, but the fine view afforded ns by the telescope will be better appreciated when we realise the importance of the stars themselves The New Zealand observations, very consistent, though few in number, show the colour of the bright star to be the same as th ' of pur while the fainter star is yellow. The bright star of Alpha Centauri is especially interesting, for it resembles our own sun so closely, with the same temperature of nearly 6,ooodeg, hut it gives 17 per cent more light, and is 10 per cent, heavier than the sun. The sun’s diameter is 865,000 miles, that of this star 9:15,000 miles, and, like the sun, it would sink in water.

The yellow member of tho system is of the second magnitude, and gives only one-third, of the light of the sun, but is 6 per cent, less heavy, and is 1,350,000 miles across. It. would float li’s a cork on water, and its temperature is 4,loo'L’g.

These .'.vo stars move round their common centre of g.avity in a period of seventy-nine years, at a mean distance of twenty-three times that which separates us from the sun. The orbit is a. beiuitilV wide oval, but, being almost “ edge on " to ns, appears greatly elongated. The Winter .Solstice, astronomically speaking the beginning of winter, occurs on the morning -f June 22, when the sun is farthest north.

The moon, in the morning sky, passes Mars and Mercury on June 2 and 3, new moon occurring on the evening of the 4tb. Passing the planet Venus on t' forenoon of the 7th, Jupiter on the evening of the 9th, and the star Regulus on that of the 10th, the moon wi.. reach first quarter on the forenoon of the 12th, and at 8.50 p.m. (14h S.T.) that evening will lie N.W. at an elevation of 34deg. Having passed Spica on the auernoon of the 14th, our satellite will occult the fifth magnitude star 42 librae on the morning of the 17th, twenty-seven minutes after midnight, pass Antares the following evening, and at 8,30 p.m. will he placed K.X.K. 56deg. The variable star X Sagittarii .. . disappear behind the moon at 10.08 p.m, on the f.Bth, a :i lull moon wilt occur at midnight. The brightest star occulted this month is Phi Sagitta-rii, mag. 3.3. It will be a grazing occult, 'ion at Dunedin, the star disappearing at 6.56 p.m. and reappearing fifteen minutes later. Last quarter falls on the evening of the 26 th.

Jupiter will soon disappear from the evening sky, being now situated W.X.W., 1 to 6 deg, at 14h S.T. At the same time Saturn will bo seen in the E.S.E. ? elevation 9 to lldeg. Venus will be stationary in the evening sky on the 7tb, and in inferior con-

junction wivh the Sun on the 29th. Mercury will be in superior conjunction on the 13th.

From the town's Garden-, Dunedin, at Hit S.T., Spica will bo seen rather high over Burlington street, Arcturus rather low over First-Church, Antaros rather high in the direction of the Early Settlers’ Hall, Alpha Centauri nearly overhead in the direction opposite to Burlington street; while at 8.30 p.m, on the 17th the Moon will shine up High street, being close to Antares.

CONSTELLATIONS OF THE EQUATORIAL ZONE

IL— CORVUS, THE GROW. This small constellation bears no resemblance to a bird, and sailor’s call it the “ Cutter’s Mainsail,'’ its four principal stars marking out such a shape, upside down to us, very clearly. The gaff, the shortest side, points to Spioa, the brightest star of Virgo. There are no first or second magnitude stars in this group, but the four principal ones arc of the third magnitude. Epsilon Corn, mag. 3.21, in the square 182.53, is a yellow star of the common type KO. Its light set out on its juorney to our eyes 120 rears ago, and tho star is sixty-five times as bright as the Sun. With a temperature ef 3,960 deg. it is twepty-six times as wide as the sun. and is tho largest of tho sis prominent stars of Corvus. In the square 183.18 we insert Gamma, mag. 2.78. belonging to the bluish typo 88. It is a spectroscopic binary of suu power 160. and its light takes 153 years to roach us. The companion star is too faint to show its own dark lines in the spectrum, but its presence renders the temperature and diameter of tho main star somewhat doubtful, though the colour is well determined. Tho temperature is probably 13,400dcg, making it the hottest of the Corvus stars we are mapping, and tho diameter three times that of the Sun. Delta, mag. 3.11, type AO, is a single sun with a tomepraturo of IS.OOOdeg, distant 110 light years, 2.2 times as wide as our Sun, and fifty-eight times as bright. Beta, mag. 2.84, is the brightest and most distant star of the group, sun power 166, diameter 20, and distance 160 light years. In the square 188.53. Its temperature is 5,030 deg and its colour light yellow (typo Go). There are two stars of the fourth magnitude in Corvus. Alpha, mag. 4.15, being of the pale blue type F2. with a temperature of 6.ooodeg. in the square 181.54. Light speeds to ms from this star in only eighty years, and though only 2.5 times as wide as the Sun it gives twelve times as much light. Eta Corn', mac. 4.42, shares the square 187.46 with Delta, being on the east side, towards Spica. ft is a spectroscopic binary in which both stars show' their dark spectral lines. ]t is the nearest of the groun, being fifty-nine ’kdit years away. Its temperature is about 6.000d0g. and tbe large star of the pair is probably about one and a-balf million miles in diameter.

In drawing this group or tracing ;t iu the sky readers will recoirnise Alpha, Epsilon. and Gamma as markina the mast, Beta and Delta the ends of the hooni and gaff of a mainsail. Alplia is very nearly in line with Epsilon and Gamma, as a fiance at the actual stars in the sky will show. The small scale of our stone sou a res does not show this scry well. The position of Bnica is :?O f VJI, and Gemma emi Delta C'orvi point i.v-ftth this hr;" 1 t star, v.h'i-h we shall describe in detail next tvionih. The name “ t'orre ■ " is contract- d by some to “ Crv." by others to “ Cor." >\ e prefer the. latter contraction for various reasons, which wc may discuss inter.