ASTRONOMICAL NOTES FOR AUGUST.

New Zealand Herald, Volume XLIX, Issue 15060, 1 August 1912, Page 3

ASTRONOMICAL NOTES FOR AUGUST.

3IT S. TIT ART, BRITISH ASTEONOiiICATI ASSOCIATI' Jx. W he.v wo casually gin co at the heavens, o. is first impression ; is ~hat the stars are absolutely at rest, 2 /t id the whole scene 53 '" 0 '- 1 '- an altogether stationary -character, There could bo no greater delusion thanibis-. Not only do the whole of tho stars 'perform a corn pic revolution about tho polar axis in twenty-four horns, but each f of them has its own proper motion as j well. And this is not .alb Tho stars j which appear ulxnit our meridian this : evening, are not the same that were .seen ; there a- couple, of inontl is ago. nor will they |be there two months banco; because in. I addition to the diurnal revolution of the heavens, there will ahp ;be an annual one as toe sun seems to . pursue his journey - round the skies. And, -h/mce, if we desire Know what stars are on or. near our meridian this evening', both these tilings have to be taken into consideration. It i.v not so difficult to ascertain our point ; because for all practical purposes we may consider that the rtivae stars which were on the meridian th js day last year at say J -4V 1 ,"" - were there l .! the previous year and' v.ill be found there, to-night. But. wo cam not make this rule.. of indefinite extension;, lor if we tried to.; do so, then a third apparent motion of /die heavens would coma into view and >' , would bo found that | the same star di-J not return to the meriI dian at just the 1 ;ame time of the day 'or night- on a Mate .cular date, nor until no Jess a period tlta 11 nearly twenty-six thousand years had elapsed", for it will take all that time / .or a given star to return to the tyjiunoj . again, after it has once occupied that point. L we adopfc a fixed hour of the evening each month, 3 nd study the stare which ars then found a bout our meridian, we may easily run through all that tu*e visible at a certain l t \<> ight above our .horizon in a year ; but ]jy changing the altitude tad/ year, _it rv<j,uld take 'us all our l/^t-s to examine - then all. Let us begin,, therefore, w/th only a. few conspicuo/js ones. 1? w>Jj m ake our time. 9 m -, ami our date Uie I,'ith pi the present month,. And' rt Y'"' bejjin low down towards t',ie "north If t.Ae sky is clear and nothing obstructs our view, we shall see a 4 few decrees above our honw.ni a brilliant 'star, Easily reeo'nißTihle by two email owes a little above Jt.tx> the right; which is, trfie principle star in . the Lyre or Jfarn, an<i known bv /the n./me of Vega: otherwise Alpha Lyra-.' it s]>ark!es 011 the border of the Milky v\ ay, and m colour it is whits, or even ■ bluiijji ' while 03 1 of. the nineteen most ■brillßint -stars in tfcfc sky, it, is the fourth m order.of brightness;, to the naked eye. Wo see it as a, star low down ,in tlio northern part of our sky ; but in the northern hemisphere there was once a -time whcai it was the' Pole Star; but that was foui teen thousand years ago, and it will bo ancfiber twelve thousand before the great cyr-le above referred- to brings it into the north pole of the. heavens again. When it does i.o, it will form the ,'easiest guide to the true north that humanity lias over nr/d; as far as the northern hemisphere is concerned—but it will be of no Use to ins in N.ew Zealand, simply because y A~e cannot see it, (since Ties so far below xmr horizon. It lias been noticed above, that the stars seem to be quite immovable; and even ' after allowing for the three motions relerred to, up to some (avo hundred years ago this ■was believed to be true. But it is not; for eveay star in the heavens lias a, true motion of its own. and probably in. immense circles, or more likely * ellipses, .bf which the time of ' revolution is for the most part entirely ■ unknown. But as our suit is ono of • j the stars, he also lias his proper orbit in the immensities of space; and to make one complete circuit of it will take him no less a time than some twenty millions of years! Because of this, and also on account of the star Vega having its own orbit, wo find that . our solar system is appiviching the star at- no less a rate than, miles per second by the combination of the two motions. And while on this subject we may note 1 the whole of the stars seem to be opening out in the direction our. system is moving, while they are. closing in 'behind us. or at the point from which we came; while 011 each side of the line of our movement they rush by us, as it were. It is just the same as when we are riding in a tram car; if we observe the houses 011 each side, as they recede into the distance they seem to close in towards each other; while those in front of the car continually open out. And so vast is the orbit of our sun, that he and the whole solar system are rushing along at some four or five hundred millions of miles per annum ; moving in what seems to us to he a straight line, but is in reality a vast curve. But to return to our star. Everyone lias noted how the stars will twinkle or scintillate; and more at some times than others, also in the cases of particular stars the same difference is observable but perhaps this takes more observation* than the casual star-gazer gives. As a matter of fact Vega is one of the stars which, scintillate most. All of them do so on the average about 70 times per second, Vega has • an average of 86. Now this is partly the ifi_'ct of our .atmosphere, and partly, arises from the -unequal rate at which rays of vvlerent colours reach tho eye, consequent upon their -varying wave-lengths. As' to that part which is due to our atmosphere, I have seen from the top of Mount Eden, the sun shining on a window at the-North Shore; and this brilliant light twinkled exactly like a star. Tho difference between the twinkling of tha window and a. star lay in the fact that tho former was not so rapid as the latter; also it had 110 changes of colour. And herein lies - an- enormous difference; 0110 which has enabled astronomers to tell us what the stare are made of. We all know how the stars seem to change colour as they twinkle; and while they may have a certain definite colour . of their own, this is varied from moment to moment to all the colours of the rainbow. Even in the case of a white star, such as the one we are studying, this is the case: and mum mere so than in tho

instance of a red star. The spectroscope, an instrument which lias the power 08 resolving any given light into its component colours—white sunlight having seven—has given us the spectrum or band of colours which - are appropriate, to each star examined; and these spectra, or colour-bands, are found to bo crossed with certain dark lines. When we burn the various metals or, gases, and take the resulting spectra, we find similar phenomena : and hence, if the spectrum of a star gives a similar result to any of these, we are at once ablu to say .what metals and gases are present in the star. And our star Vega has a spectrum of the same kind as Sirius, and it i<> as full of lines as the solar spectrum itself. And these lines, in the case of this star, indicate the presence of hydrogen, sodium, and magnesium, all of them at a high temperature. From which (among other circumstances) it appears that this star is a vast, and brilliant sun, doubtless surrounded with it? attendant planets, as is our own. There things mark the difference between our study of the stars and that of the ancients; who looked aporj them with a different phase of 'bought.. They were aware of the periodical motions above described, and consequently that the rolling year presented a panorama of changing skies, varying from century to century as well. And of these <~ha.igeg they made maps or planispheres, which in some few instances have come down to our times ; thus enabling us to determine by our nearly perfect scicnce, the epochs to which these ancient maps belonged.) But among other things which oiu? studies of these ancient relics have given: us, is a most important one; for it has been discovered that upon the changes of the year and the varying aspects of the skies, the antique systems of mythology and the pagan religions have been built up; and Bulwer Lytton, in his "Last Days of Pompeii," makes Arbaces say that upon these things his Egyptian ancestors had founded an august allegory, of human life and destiny, and dodueed religious and) political rules and maxims by aid of which they con- . trolled the ignorant, and tho priests _ secured their powers. No 0110 would' .. * now dream of ' using the stars fcWjfcg I such purposes; but these were eminea-.y 111 keeping with the times in which hey originated, and form, a study of enthralling interest to those competent to deal W.Lh if. /.