ASTRONOMICAL NOTES

Evening Star, Issue 21966, 28 February 1935, Page 3

ASTRONOMICAL NOTES

THE SKIES IN MARCH (Written by A. G. C. Crust, M.Sc., for the ‘ Evening Star.') POSITIONS OF THE STARS Local sidereal lime Shrs., latitude 46deg 8. . . ~ , The following star positions hold good locally four minutes earlier, each , day, as at 10 p.m, on March 3, if P.m. on March 18, and 8 p.m. on April 2. Achernar is now placed ods,!*., 22deg, Canopus S.W. by YV., <<>deg, lligel N.W. by W., 37dcg, and Aidebaran N.W., 12deg. In the N.W. by N. Betelgeuse is 29deg above the horizon, and ‘Sirius 2Sdeg higher still, while Procyon is N. by W., 39deg. Due north shines Pollux, at an elevation of 16deg, while Regulus lies N.E. bji JN., 26deg, Spica E.. 15deg, Alpha Crucis 5. SOcieg, and Alpha Centaun fe.E. by 8., 35deg. ; , . . , The Moon will be in the morning sky at the beginning of the month, and pass very close to Mercury early on March 4, while' on the evening of that day slio will- pass , the planet Saturn. New Moon occurs on the afternoon of March 6, when the Moon will be 27deg north of the star Fomalhaut, while on tho afternoon of the 7th she will pass odeg north of the bright planet Venus, "he Moon will pass Aldebaran on the afternoon of the 11th, first quarter will occur at mid-day on the 12th, and at 9.20 p.m. on'the 13th the Moon will appear N.N.W., IGdegy Passing Pollux on the morning of the 15th and Regulus on the forenoon of the 18th, the Moon will be placed N.E., 28deg, at 9 o’clock that evening, while Full Moon will occur on tho afternoon of the 20th. On the evening of the 22nd Spica will be seen 3deg north of tho Moon; at 8.4 c) p.m. on the 23rd our satellite will appear E. by S., lOdeg; early on the 25th .she.will pass the planet Jupiter; and .last, quarter will be reached on the forenoon of the 28th. Autumn begins on the 22nd at 1 a.m., when the Sun • crosses the Equinoctial into the Northern Hemisphere. The planet Mercury will be in the morning sky, stationary among the stars on March 1, and at greatest obligation west of the Sun, 28deg, on the 15th. A conjunction with Saturn will occur on the evening of the 22nd. The planet Venus will be visible _in the early evening sky, but still setting before the epoch of our star positions. On, the evening of the 22nd she will pass only o.4deg to the north of the faint and distinct planet Uranus. The planet Mars now appears, at Bhrs S.T., in the eastern sky, his position changing from E. 9deg, at 10 p.m. on March' 3, to E. by N., 12deg, at 8 p.m. on April 2. He is retrograding, or moving westwards among the stars. On the 12th he will pass G.ldeg south of Zeta Virginis, and on March 23, s.3deg north of the bright star Spica. The planet Jupiter ,will not come into our positions for Bh'rs S.T. until the beginning of April, when he will bo rising in the E.S.E. He will be stationary in the morning sky on March 10, when his retrograde motion will commence. The planet Saturn is in the morning sky, and still close to the Sun. From the Queen’s Gardens, Dunedin, at Bhrs S.T., Canopus appears very high- ■ over Burlington street, white Alpha Centauri is moderately low in the opposite direction, and Pollux is low over First Church. Mars will he low over the Early Settlers’ Hall at 8 p.m. on April 2, the Moon rather low over the station at 9 p.m. on March 18, and low over Rattray street (seawards) at 8.40 p.m. on the 23rd.

CONSTELLATIONS OF THE EQUATORIAL ZONE XXVII TO XXIX, BOOTES, HERCULES, AND SAGITTA. Bootes, the Herdsman, is a constellation that extends far into the northern regions invisible in our latitude. Its brightest star, Arcturus,' has already been described, but the colours of three more have been measured. The third magnitude star Eta Bootis is probably most noteworthy as the nearest spectroscopic binary. Its magnitude is 2.8, type GO, and distance 33 light years, zone position 207,12. In colour it is white, and its radial velocity varies in a. period of 497 days, from which the mean distance between the two stars ot the system is calculated to be: 1.68 times the distance from the Sun to the Earth, or 156,000,000 miles. The total sunpower is 7.2, and the following figures, based on the known colour and the position of the system in the Russell Diagram of stellar evolution, are perhaps as near to the truth as we can approach for many years to come. Both stars are about 5,970 deg effective temperature, the larger one having adiameter 2.4 times that of the Sun, the smaller 1.2 times that of the Sun. In the square 207.14 wo may plot Epsilon Bootis, of mag. 4.3 and type lvs, a yellow giant 270 light years away, of sunpower 120 and temperature 3,460 deg absolute, with a diameter fiftj'-six - times that of the Sun. Zeta Bootis, in the square 220,16, is a visual binary of type A2, the magnitudes of the two stars being 4.4 and 4.8, and the, distance 250 light years. The pair of stars revolve round their common centre of gravity at a mean distance forty-nine times that of the' Sun from the Earth, in a period of 130 years. The brighter one is ninety-one times as bright as the Sun, the fainter sixtythree. The combined, colour is well determined, but the temperatures and diameters of the separate stars are obtained by the help of the Russell Diagram, and may be confirmed by later observations. The, brighter star is probably the cooler of the pair, with a temperature of 10,300 deg, while the fainter one is 12,600 deg, These values would make the brighter star 3.6 times as wide as the Sun, and the companion 2.3 times the solar diameter. Hercules is another northern constellation, partly visible in our latitude. The name of the well-known Greek hero and demi-god was given to it in modern times. The Greeks themselves called it “The Unknown .Form,’’ and the Arabs “ The Kneeler.” It is represented as a man kneeling and holding a number of snakes at arm’s length, while holding a club aloft with the other hand. This region lies north of Ophiuchus. Alpha Herculis, or Ras Algethi, “ The Kneeler’s Head,” is a variable star of a reddish orange colour, which should be mapped in the square 258.16. In magnitude it varies from 3.1 to 3.9, and appears to be of the irregular type, though a period of 120 days has been suggested. Revolving around it in a very long period is a star of type G and mag. 5.4, whose radial velocity varies in a period of 51.6 days. The main star varies -in sunpower from 1,100 to 525, its light taking 470 years to travel -to our eyes, and its type is Mb. Its surface temperature is about 3,ooodeg. and its diameter 270 times that of the Sun, or 234 million miles. The companion star yields 140 times the light of the Sun. In the square 281.10 we map 110

Herculis, of type F 5 and mag. 4.3. It is fifty light years distant, and five times as bright as the Sun, its temperature being 7,olodeg, and its diameter 1,360,000 miles. In the square 281,12 may be'mapped 111 Herculis, of mag. 4.4 an.d type A 3, seventy-four light years distant and having a variable radial velocity. The colour of 111 Herculis is bluish, and the most probable values of the two separate stars are as follow:—Sunpowers 6.9 and 1.7, temperatures 10,900 and 7,960, diameters 0.91 and 0.73 of that of the Sun, or 790,000 and 630,000 miles. This system seems to be tending towards the dense dwarf state, of which the companion of Sirius is the best-known example. Sagitta, the Arrow, is an ancient astensm lying immediately to the north of Aquila, the Eagle. The colours of three of its fourth magnitude stars have been measured. Alpha, in the square 294,13, of mag. 4.4 and type GO, is so far off that its light lakes four centuries to travel to our eyes, so that the light which will arrive from it this winter has been travelling since the most stirring years of the Spanish conquests in America. It is a pale yellow giant of 250 sunpower, seventeen times as wide as the Sun, with a temperature of 5,760 deg. Beta Sagittae, also of mag. 4.4, in the square 295,13, is of type KO, yellow in colour, and_ distant 230 light years. It is seventy-six times as bright as the Sun, and thirty-three times as wide, its temperature being 3,750 deg. In the square 296,12 we map Delta, of mag. 3.8, and the composite type Ma, AO. Composite spectra betray the presence of at least two stars, usually of very different types, where only one appears to the telescope. The difficulty in interpreting the' colour, however carefully lies in the question of the relative brightness of the two stars. Presumably there may be a great difference in the brightness when the spectra are so different that the brightest part of the faint one may he superposed on n weak region of the bright one, as may well be the case here. The following figures are based on an analogy with two systems which present a much smaller difference between primary find secondary, and the colour of the secondary is assumed to be the normal value for its type. The primary is probably at a temperature ! '-of 2,710 deg, and 220 - times as wide as the Sun, while the secondary is assumed to be at ll,2oodcg, and 1.7 times the width of the sun. The sunpowers are 205 and 25. The light from this system takes three centuries to reach us. These constellations are invisible at the present season. 1