ASTRONOMICAL NOTES

Evening Star, Issue 20136, 28 March 1929, Page 12

ASTRONOMICAL NOTES

THE SKIES IN APRIL [Written by A. (J, C. Cjiust, M.Sc., lor the ‘ livening Star.’] On April 1, at 8 p.m., the Moon is in conjunction with the planet Saturn, and reaches last quarter at 7 p.m. on the 2nd. A conjunction of the Moon with Uranus at il a.m., and one with Mercury at 3 p.m., occur on the. 9th, while New Moon Falls on the 10th, at 9 a.in. The Moon passes Venus on the 11th at (1 a.m.. Jupiter on the 12th at 4 a.m., Aldcharan on the IJth at 9 a.m., Mars on Die Itith at S a.m., Pollux twelve hours later, and lir.st quarter occurs on tho ]7th at 2 a.m. On the 19th our satellite passes Itifgulns and Neptune at 8 a.m., on. the 23rd Spica at 10 a.m., and Full Moon comes twenty-four hours later. The- waning moon passes An tares on the 27th at 7 a.m., and Saturn on the 29th at 3 a.m. The planet Mercury is very close to the Sun during the month. .He passes the planet Uranus on the Bth at 9 a.m., and on tho\l7th is in superior conjunction with the Sun. Having entered life evening sky, ho passes Jupiter on the 29th at 2 a.m. The planet Venus is drawing near to Ihe Sun, and appears as a, slender crescent in the telescope. She is so far north that it is best to look for her long before dark. She is in inferior conjunction with the Sun on the 20th, ami enters the morning sky. The position of the planet Mars is still given in onr notes. The planet Jupiter is drawing near to the Sun, but the splendid ringed planet Saturn may he seen in the oast late at night, ami. indeed, just escapes being included in onr positions. He is stationary on the 9th, and his position will he given next month. Those who arc interested in the distant planet Neptune will have a good chance to look for him this month, for on the 121 h ho is situated nine minutes of arc north of the bright star llcgu--Ins. given in onr notes. The Sun has shown great activity in ihc past month, one group of spots being surrounded by a' penumbra 43,000 miles across. POSITIONS OF THE STARS Sidereal time, I l ' hour.-': latitude, ■Kklcg S. The following positions hold good tor April 9 at 9 p.m.. and April 21 at S p.m., am! four minutes earlier per day, for oilier dales, at Dunedin : Hegulus. brightest star of the hy-cyck'-likc Lion, is due north, altitude ;{’;>deg, the brilliant A returns is flaming redly in the N.E. by E.. altitude 3deg. and the beautiful bluish star Spirit lies E.N.E.. altitude 36dcg. Above Si'»ica arc the lour conspicuous stars of the little group Corvus, known to seafaring men as “The ('utter’s Mainsail.” The two closest of the four stars, forming the gaff, always point to Spica. The lifelike form of the Scorpion is now to be --0011 in the east, its bright red star, Antares, being K.S.E.. lodes. The Scorpion is an appropriate herald of frosty nights. ’Hie nearest star to the earth, Alpha Oentanri, is BLK.. dOdeg, while the Southern Cross is S.F. by S.. dodeg; Aehernar, S.S.W.. 22dcg; Canopus, S.W. by \\ oddeg: Nigel. W. by N.. 18deg; Sirius and 'nelelgue.se. VT.X.W.. -lOdeg and 14deg respectively. The difference of 2(ideg between these two stars should help readers to follow the altitudes given in these Holes. Hid:ween Uctelguese and IJjge! shines the well-known “ frying pan” of Orion. The “(treat Nebula ' of Orion is the hazy middle star ol the ''handle." Procyon is N.M.. alt. 30deg. This is one of mil' nearest stellar neighbours, and. though it. is a, binary whoso weight has been very well determined, the result, does not agree well with the brightness of the star, according to the calculations ol Professor Eddington. Recent observations of the colour of the star suggest that., there is an invisible companion, whose presence may alfect, these matters considerably. Owing to the lateness of the season we may have to wait another year before the presence ol this companion star can he proved beyond doubt. Our hist bright star is Pollux. X’.Vi . by X., tOdeg. ,/ On 1 April 9. at 9 p.m., the planet Mars is N.W.. alt. Sdeg.. and on the 24th. at 8 p.m.. Mars is X.V . by X., alt. !3deg. . On April 2-1 th the full Moon is L. by X. at 8 p.m.. alt. 2(ideg.

METHODS Of OBSERVING VARIABLE STARS Tin l oh-crva linns of vn I'inlilo 'liiin i'll verv ]n 11 Kut :i n I work, and its jni|mrl nme I' rivalled only by it ' mihplicil \-. There is no need lor costly aplin rn Ins lor telescopes of nil size', binocular-, Mini oven the unaided eye, may find m Held for this work in the Sunt horn 1 leinisphere. A good knowlodgo of the mimes of the brighter stars :ind m set of special charts supplied hv the variable star section of the New Zealand Astronomical Society, completes the necessary equipment. Air .I'. Al. .Bateson, box .! .TUI, Wellington, the director of the vanable. star section, is willing to give instructions to i'ntending observers as to the geography of the brighter stars, a. knowledge ol which is essential. _ Having found tin; place to which his variable star chart refers, the observer , points his binoculars or telescope in that _direction, and locates the stars marred on the chart. In some cases the. variable is distinguished by its redness as well as by its position. On the chart the “ comparison stars,” whose nnwinilndes are well determined, are usually lettered a. h, e, etc., and a list of fhe stars, with their magnitudes, is given. The. finding ol the stars on the chart is an initial dimcnltv which should not discourage the observer, for once he has obtained a geographical picture of the region he wdf have no trouble in finding the locality again, and whereas his first observation may take him halt an hour ami not ho a good one, all Ins subsequent ones will take up less than live, minutes each, and .should be quite reliable. .. Thu variable and the surrounding stars having been located, the observer concentrates his attention on the brightness of the stars. hie notices perhaps that the variable is not as bright as the comparison star b, hut is brighter than the comparison star c. He now proceeds to compare -the three stars concerned. According to the method used m Australia ami New Zealand, he looks from the star b to the"'star c, and judges ( that there are, say, five “ steps or brightness between them. Ho may decide on three or seven steps, preferably as an odd number, according to the amount of the difference. r Jhc variable is judged in the same way with reference to both b and e., thus being “ tied in.” For example, the

variable may appear three steps fainter than h and two steps brighter than c, Tlie. observation is recorded “ h 3 V 2 c.” In such .recording the brighter comparison star comes first, then the mimber of steps down to the variable V. then the number of steps down to 11 10 fainter comparison star, which is written last. In practice the observer records lor each star the date and time of observation, the size and power of his instrument, then the comparison, in this case h 3 V 2 c. Jf the magnitude of h is d.b, and that of c 4.0, the resulting magnitude of the variable is readily seen to be 3.8. A star as bright as this can readily he observed with tbe naked eye, and this example is taken from a variable, 1 Carina?, w hich can always be observed without a telescope. It is important, in estimating the intervals of brightness, to move the bead in looking from star to star, not to roll the eyes, and, in using a telescope, to bring the stars each in turn to the centre of the field. It is best to look steadily, but not too long, at each star. It is highly desirable that we should have more variable star observers in the south of New Zealand, and observations from Dunedin and from Central Otago would do much to emphasise the astronomical value of those districts. The writer, while testing sites for an observatory in Otago and South Canterbury secured hundreds of observations of this kind, giving good evidence of the. worth of the. climate, apart from the other excellent tests which Avero obtained.'