ASTRONOMICAL NOTES

Evening Star, Issue 21090, 30 April 1932, Page 3

ASTRONOMICAL NOTES

THE SKIES IN MAY POSITIONS OF THE STARS [Written by A. G. C. Ceost M.Sc., for the ‘ Evening Star. ] Local Sidereal Time, 12 Hours, Latitude 46deg S. The following positions hold good four minutes earlier per day, from IU.oU p.m. on May 2 to 9.30 p.m. on May IV’, and 8.30 p.m. on June 2. Achernar is now S. by \v., delation 15deg; Canopus, S.W. 38deg; Sirius, W. 19deg; Frocyii, W.N.W. 13deg; and Eegulus, N.W. by >i. -bdeg. Eegulus, or Alpha Leonis, is a bright, hot, hydrogen star of type BS. It is of mag. 1.34, and is accompanied by an eighth mag. star of type KO, with the same proper motion, at a distance of l 7 7sec of arc. This second star is a binary, having a companion of the thirteenth magnitude at a,distance of 3sec of arc. The light from this system of stars takes fifty-nine years to cover tho distance to our earth, and, though not very impressive as a telescopic object, the system is remarkable for the great contrasts between its members, especially in brightness. The bright star which has been recognised for ages as Eegulus is ninety-one times as bright as our sun, which, on the other hand, is five times as bright as the eighth mag, companion and five hundred times as bright as the faint star revolving round the latter. With a temperature of 13,800 deg, and a diameter of 2.5 times that of the sun, as measured in New Zealand, Eegulus is indeed a magnificent star, and its companion, with a probable temperature of about s,ooodeg, should have a diameter of only about five hundred thousand miles; but, strange to say, if the isokatatypes may be relied upon, the faintest star of the system is about the same size as Eegulus itself! Its temperature is likely to be about 2,700 deg. Eeaders will remember that the sun is 865,000 miles across. ~ ~ , Spica is now N.E. by IN. oldeg; Arcturus in the same direction, but 33deg lower; Antares due east 34deg; Alpha Centauri S.E. 64deg; and Alpha Crucis S. by E. 73deg. The Moon will be in front of the faint star 60 B Piscium (Use), which will reappear at 4.53 a.m. on May 2. After passmg Mercury and Mars on May 4 our satellite will be at “New’ Moon ” on the morning of the 6th, will pass Venus on the morning of the 10th, and will be placed N.W. Bdeg at 9.10 on the evening of May 12, while Jupiter will be passed by on the 13th in the forenoon. First quarter will occur on the morning of May 14, Eegulus being close to the Moon by noon, while at 9.30 p.m. on the 17th the Moon will be found N.N.E. 51deg. At 12.46 a.m. on the 18th Virginis, mag. 5.6, will disappear behind our satellite, which will pass very close to Spica on the morning of the 18th, occulting the star for South African observers, and 40 H Virginis, mag. 5.1, will be occulted here at 3.49 a.m. on the 19th. Full Moon occurs on the evening of the 20th, and Antares will be occulted in South Africa early on the 21st. At 9.50 on the evening of the 22nd the Moon will be E.S.E. 18deg, will pass Saturn on the morning of the 25th, and reach last quarter on the afternoon of the 27th.

Mercury will be in conjunction with Uranus on the morning of May 7, at greatest elongation west on the Bth, and in conjunction with Mars on the 19th, while Venus will he at her greatest brilliancy on May 22. She must be looked for very early in the evenings. The only bright planet at. 12 hours S.T. is Jupiter, now situated N.W. 15deg to 17deg. The superior conjunctions of his satellites take place as follow:—lo, first, May 1 22h 57min; seven" ienth, May 30d 7h 44min; Europa, first, May 4d 13h 41min; eighth, May 29d lOh 52min; Ganymede, first, May 4d llh 32min; fourth, May 25d 23h 45min; Callisto, first, May 4d 3h 30rain, second May 20d 21h 54min. Callisto will be at greatest elongation east on May 7 and 23, and west on May 15 and 31. The most important eclipses of the satellites are two, that of Callisto by Ganymede occurring from 8.08 to 8.51 p.m. on May 4, and that of Ganymede by Callisto from 8.27 to 9.22 p.m. on May 29. lo will be occulted by Europa at 11 p.m. on May 5, Ganymede by Europa at 6.58 p.m. on the 11th, Callisto by Ganymede at 6.10 p.m. on the 21st, lo by Ganymede at 8.18 p.m. on the 23rd, Ganymede by Europa at 6.20 p.m. on the 26th, lo by Europa at 6.58 p.m. on the 28th, and again at 9.9 p.m. on the 29th.

From the Queen’s Gardens at 12hrs, S.T., Achernar may be seen low over Vogel street, Procyon low over the upper end of Rattray street, Eegulus and the stars of Leo rather low up Burlington street, Arcturus low- and Spica moderately high over the railway station. The Moon will shine up Rattray street from rather low elevation, at 9.50 p.m. on May 22.

CONSTELLATIONS OF THE EQUATORIAL ZONE

I.—LEO, THE LION. Leo, the Lion, is one of the constellations of the equatorial zone, as we defined it in a recent article on the mapping of the stars. The constellation is supposed to represent the Neraean lion slain by Hercules, but has been recognised as a lion from remote antiquity, being of the zodiacal groups. Readers who intend to follow our scheme of mapping the stars will remember that the Equatorial Zone has a width of 60deg, represented by sixty small squares of graph paper, and a length of 360 deg, represented by 360 small squares. Regains, the principal star of the Lion, and the only one of the first magnitude, is in the square 151,18—i.e., the one hundred and fiftyfirst to the right and the eighteenth from the bottom.

In this constellation there is only one star of the second magnitude. It is Beta Leonis, or Denebola, mag. 2.23, position 176, 15, and type A2. Separated from us by a distance of thirtyfour light years, it is the nearest of the bright stars in Leo, its temperature is lOjlOOdeg, and it gives thirteen times as much light as the Sun, though its diameter is only 1.4 times that of the Sun.

Of the third magnitude stars, Gamma Leonis, in the square 154, 10, is one of the most interesting, being a binary star with a period of about four centuries. The magnitudes of the two stars are 2.6 and 3.8, and the distance from the earth is covered by light in 140 years. The large star is a magnificent yellow giant 140 times as bright as the Sun, while the sun-power of its companion is fifty, but there is a still brighter star among the prominent ones of the third magnitude. This is Epsilon, square 146, G, mag. 3.12, 270 light years distant, and sunpower 360. Its typo is GOp, similar to that of our Sun, but peculiar in some respects. The bluish Theta Leonis, in the square 168, & di is }3O light

years, and with a diameter 2.5 times as great as that of the Sun, gives sixty-three times as much light as the latter, for its temperature is 12,000 deg. The fourth magnitude stars are ten in number. Lambda Leonis is aKS giant 200 light years away, in the square 142, 7, mag. 4.48. Perhaps the most interesting star in the whole constellation is Omicron Leonis, mag. 3,76, in the square 145, 20. This has a composite spectrum, F 5, A 3, and since the masses are known we are able to deduce the brightness of the two separate stars. The F 5 star is about eight times as wide as the and forty-four times .as bright, with a temperature of about 5.400 deg, the A 3 one three times as wide as tho sun, and twenty-three times as bright, with a temperature of 7,400 deg. Omicron Leonis is 160 light years away, and its combined mass is nearly five times that of the Sun, while the stars revolve round their common centre of gravity in only 14.5 clays. Therefore they must be only eighteen million miles apart, far too close for any telescope to separate them. Mu Leonis, like Lambda, is a yellow giant, mag. 4.10, and 150 light years' distant. Its sun power is 44, Lambda being 58, and Mu is situated in the square 147.4. In square 151, 13 readers may insert Eta Leonis, mag. 3.58, type AOp. This bluish star of unknown distance has a temperature of 9,500 degrees, rather low for its type. Zeta, in the square 153’17, is a spectroscopic double, of magnitude 3.65, and type TO. It is sixty times as bright as the Sun, and its light takes 220 years to reach us, while Eho, a helium star of type EOp, with the strangely low temperature of 10,300 degrees, and a diameter 5.3 times that of the Sun, is in the square 157,21. its sun power is 190. In the square 165,10 we may insert sixty Leonis, a hydrogen star 230 light years away, and seventysix times as bright as the Snn, while Sigma, at 170,24, mag. 4.13, has a temperature of about 12,000 degrees, and is 220 light years away. it is nearly three times as wide as the Sun, and has an invisible companion revolving round it, the period being probably about seventeen days. *ms system has a sun power of 90. lota Leonis is a binary system, magnitudes 4.1 and 5.8, three seconds of arc apart in the telescope. The bright star is 6.3 times as bright, and three times as wide as the Sun, with a temperature of about 5,500 degrees. The companion is only half as bright as the Sun, but probably much cooler and larger. This star should be plotted at 17019, and its distance is fifty-seven light years. Tho last star on our list for this constellation is Upsilon Leonis, 173,31 of mag. 4.5. It is a KO giant, 180 light years’ distant, and forty-four times as bright as the Sun. Having given all the stars of Leo down to mag. 4.50, we may now describe the arrangement of these stais and explain the figure of the Lion as it may be drawn from them. The stars Alpha (Eegulus), Eta, Gamma, Zeta, Mu, and Epsilon form a group popu larly known as tho “Sickle,” the line from Alpha to Eta forming the handle and the remaining stars the long curved blade. In the classical figure of a great lion striding through the heavens, unfortunately upside clown to us in the Southern Hemisphere, Lambda Leonis is near the tip of the animal’s nose, Epsilon near the eye, while Mu, Zeta, and Gamma follow the curve of its mane, and Eta is on its chest. Omicron and Eho mark its forefeet, and one of its hind legs is marked by the line of stars Theta, lota, Sigma, and Upsilon, while Delta and Beta mark its abbreviated tail. The ancient constellation w f as rather longer, including the faint misty group to the east, now known as Coma, as the tip of its tail. Headers who have plotted the stars as given may check them by drawing a lion with the stars as a guide, and we hope that they tuII easily recognise them in the actual starry heavens. To the amateur astronomer the “ Sickle ' is a most striking group, as is also the quadiilateral formed by Delta, Theta, lota, and Beta Leonis, while Eegulus himself is very prettily set in the centre of the triangle formed by Omicron, Eta, and Eho.