ASTRONOMICAL NOTES

Evening Star, Issue 23179, 31 January 1939, Page 15

ASTRONOMICAL NOTES

THE SKIES IN FEBMIAHY [Written by A. G. C. Crust, M.Sc., for ‘ The Evening Star.’] POSITIONS OF THE STARS Local sidereal time 6hr, latitude 46deg S. The positions of the stars will bo the same as predicted for last month (January), four minutes earlier each evening, as at 10.00 p.ra. on February 1, 9.00 p.m. on February 16, and 8.00 p.m. on March 3. The Moon, at 10.00 p.m. on February 1, will be due north, at an altitude of 24deg, at midday on the 3rd she will pass 12deg S. of Pollux, and Full Moon will occur on the evening of February 4. On the evening of February 5 our satellite will pass S.odeg S. of Regains, her position at 9.40 p.m. on the 6th will be E, by N. lOdeg, and she will attain to last quarter phase on the afternoon of February 11. Early on the 13th she will pass 2deg N. of the planet Mars, and on the afternoon of the 15th 2deg N.-of'tho planet Venus, New Moon occurring on the afternoon of February 19. At midnight, February 20-21, the Moon will pass 4deg N. of the planet Jupiter, and on the afternoon of the 23rd sdeg N. of the planet Saturn, her position at 8.20 p.m. on the 26th being N.W. by N., 19deg. First quarter occurs on the afternoon, of February 27, when the Moon will be 3deg N. of Aldebaran. The planet Mercury will be in superior conjunction with the Sun on February 19. The planot Venus in February will be the most prominent object in the early morning sky, where also Mars is -situated. Jupiter is still in the evening sky, but is drawing close to the Sun. ■ The only planet visible at 6hr, S.T., is Saturn, which is placed W. by N., 7 to 9deg. Hitherto no predictions have been given in these notes in connection with the duration of day and night—e.g., the times of sunrise and sunset. Jt is considered that as sunrise and sunset are not occasions of special interest to many city dwellers, being best observed at sea, while the time defined in the ‘ Nautical Almanac ’ as “ Nautical Twilight ” is of importance to all who are really interested in the stars, for it approximates closely to the times at which several types of observations may he commenced, this epoch, at which the Sun is 12deg below the horizon, may be worthy of prediction. * Nautical twilight ends at Dunedin at 9.29 p.m. on February 1, at 9.13 p.m. on February 16, and at 8.31 p.m. on March 3. .

From the Queen’s Gardens, Dunedin, at 6hr, S.T., the planet Saturn will' appear very low over Dowling street. At 10.00 p.m. on February 1 the Moon will appear rather low over First Church, at 9.40 p.m. on February 6 she will be low over the Early Settlers’ Hall, and at 8.20 p.m. she will be low over Burlington street. At these times and all others coinciding with 6hr, S.T., the stars will be in the positions given for January.

THE SECOND MAGNITUDES TARS OF THE SUMMER SKY

Fn these notes the object of helping readers who have no knowledge of the starry skies to recognise the principal stars and constellations is constantly kept in view, and the “positions of the stars ” ate given every month for this purpose. Also descriptions of many of the constellations, including all stars down to the fourth magnitude, have been given from time to time, with complete directions for mapping them and relating the maps to the actual appearance of the sky. These descriptions may have been too elaborate for many of our readers to attempt to follow, but on the other hand it is certain that the “ positions of the stars ” are the last word in simplicity—too simple, indeed, for those readers who would like to have a really general knowledge of the starry sky. . In this article an attempt is made to provide an intermediate type of description. If it is asked why a knowledge of the heaven should be so desirable an item of information, the answer lies in the astonishingly rapid progress of astronomical research in New Zealand today, when the mounting tale of discoveries demands all the skilled attention of the present observers, almost to the exclusion of efforts to train more observers in New Zealand, or to make the results known at home or abroad, if the discoveries of to-day are to be exploited m the near future as they could and should be, in New Zealand, a reserve of people who know their stars is a fundamental necessity. _ With such knowledge acquired, it is a relatively simple matter to become proficient in some of the techniques now open to the amateur astronomer in this country. In the ‘ Positions of the Stars most of the first magnitude stars are given, but there remain Beta Ceutauri and Beta Crucis, the former between Alpha Centauri and the Southern Cross, and the latter the brightest but one, Alpha, in the Cross, forming its lower arm at the present season, while Alpha marks its foot. The orange star at the head of the Cross, Gamma Crucis, is of the second magnitude—mag. 1.6. At 6hrs Sidereal Time the Cross lies on its side in the south-east, at a moderate altitude, the well-known pointers Beta and Alpha Centauri being below it. It is very convenient to locate the second magnitude stars by “ alignments ” with the first magnitude ones, for, unlike the “ positions ” given each month, these alignments hold good whenever the stars concerned are visit a line be taken from Alpha to Gamma Crucis—i.e., from the foot to the head of the Cross—and produced as far again, it will reach a point at present a little above Gamma Centauii, a binary of combined magnitude 2.4 and period 203 years. These are a pair of equal bluish stars. A hue from Gamma to Beta Centauri, produced as far again, falls a little below an orange star of mag. 1.9, Alpha Trianguli Australis, which, with two third magnitude stars towards Alpha Centauri, forms the Southern Triangle. . A line from Beta to Alpha Crucis, produced about four times as far again, comes to the bluish Beta Carinas, of niiii'. 1.8 A line from Alpha Tnanf'uli Australis to Beta Car., produced one third as far again, reaches Epsilon Canine, of mag 1.7 and orange in colour, while on the same line, about as far on again, is Gamma Velorum, of mag. 2.2, with a companion of mag. 4.8. Gamma Velorum is a blue star whoso remarkable spectrum contains bright helium lines. Epsilon Car. stands at the foot of a large “cross frequently mistaken for the Southern Cross, and so termed the “ False Cross.” At the head of this cross stands a tlurd magnitude star, but its lower arm is marked by lota Car., of mag. 2.2 and pale blue in colour, while Delta Velorum marks the upper arm. being a blue star of mag. 2.0, with a companion of mag. G. 3 revolving around

lit. Car. and Delta Vel. point towards Gamma Velorum. A long line from Gamma Centauri to Alpha Trianguli Australis, produced almost as far again, brings us to Alpha Pavonis, an eclipsing variable whose romantic story we hope to relate in next month’s notes. It is blue in colour and of mag, 2.1. A lino from this star to the first magnitude star Fomalhaut passes through the constellation Grus, the Crane, containing two second inagnitude stars a little above this line. Doth are of mag. 2.2, Alpha, the nearer one 1 to; the line, being blue, andi Bete. orange. Returning to Alpha Pavonis, wo may notice three fourth magnitude stars on the poleward side of. it —i. 0., towards Beta These form with Alpha Pavonis a 11 trident, ’ which, with the Cross, and Pointers, ; Canopus and Achernar, fornv four seasonal groups always visible in the southern, sky. Canopus is the highest in the summer evenings, the Cross in autumn, Pavo, the “ trident,” in winter, andi Achernar in spring, i The bright constellations in the i neighbourhood of the well-known 1“ Pot ” or “Prying Pan,” which is the central portion, of Orion, are the distinctive stars of summer. A line from Iliget to Betelgeuse is> bisected by the three stats Delta, and Zeta Orionis, forming the Belt of Orion, and. all' of the l second 1 magnitude. Forming a quadrilateral with Rigel and Betelgeuse, the figure being almost a trapezium, completely enclosing the “ Prying Pan,” we have Gamma Orionis or Bellatrix forming the obtuse lower left-hand corner, and Kappa forming the upper right-hand, _ rectangular corner. A line from Sirius to Aldebaran passes Just below the Belt of Orion near its mid-point, so that the Belt itself helps to point out those two bright stars, while the second magnitude star Beta Tauri is directly north of Bellatrix, and forms an isosceles triangle with the two orange giants Betelgeuse and Aldebaran. A line from Betelgeuse to Sirius produced half as far again reaches Delta Canis Majoris, one of a triangle consisting of Epsilon Canis Majoris to the left of the line, and a third magnitude star further on. Another star to the loft of the line, but near Sirius, is Beta CMa. or Mirzam, the Announcer, socalled because it rises shortly before the brilliant Dog-star. _ A line from Bellatrix to Zeta Orionis produced twice as far again falls close to Mirzam also. Almost halfway between Beta Tauri and Procyon shines Gamma Geminorum, of the second magnitude, a star which is also halfway between Bellatrix and Pollux. If this latter line is followed down to Pollux, and then a turn made downwards at right angles to it, the bluish second magnitude star Castor, or Alpha Geminorum, is soon encountered. This is a remarkable multiple system of stars consisting of two spectroscopic binaries revolving around each other in a vast visual orbit, while an orange dwarf eclipsing variable shares their proper motion. All the second magnitude stars in the region surrounding Orion are blue or bluish in colour, except Delta CMa, which is practically white.

THE NEW ECLIPSING VARIABLES IN FEBRUARY

The principal eclipses of Lambda Eridani commence 3.4 minutes earlier daily, as on February 5:00:00, 14:23:25, and 24:22:52. These terminate on February 5:04:13, 15:03:39, and 25:03:00. All times are given in New Zealand summer time counted from midnight to midnight. For Mu Orionis the Universal Ephemeris gives February 15:02:54 and 24:00.43 as times for the beginning of eclipses, while alternate ones terminate on February 11:00:54, 19:22:34, and 28:20:15. A secondary minimum of Rho Hydne will commence on February 27:02:54. Alpha Volantis varies 11.9 mm earlier each evening, primary minima beginning on February 6:23:54, 16:21:55, and 26:19:57, for example. Theta 2 Crucis begins secondary minima on February 4:23:45 and "22:04:37, primary minima on February 4:00:45, 10:21:54. and 28:02:47. T’econt observations of 32 Orionis show the period to bo 4.95 G da vs, but the amended ephemeris shows the primary minima to be too early for observation in the south of New Zealand in February. This is true also of 37 Orionis, for which a period of 8.972 days has been found.