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Show T- I Kje-. - ; - t VWajjMrMlfMHraw HOW ASTRONOMERS -. . MEASURE STARLIGHT (Cmilirlilge. Muss. Letter.) On, of the must Important and Interesting. Inter-esting. d,p:irlm,nf s of astronomy as ll as one of the least known pupil-lirly-.i the measurement and record-lug record-lug of the comparative magnUude of tha . ..... ..!... .... i .. Hd on. doubtless, since the beginning rt aitmnnmlcgl science. In this reik-"lng reik-"lng of magnitude, which Is known ai photometry- the measurement, that of starlluhl -It Is Interesting lo fste thst an American astronomical (tshiuhment stands among the flrt, 1' Sot as the very first In the world. I plotnmetry having been for years one of the principal subjects taken "P by " Harvard Observatory. Imili In Cunbrlilge and at Arequlpa. Peru, and tl results of the work which II haa etomiillshed having been accepted as iiadard all over the world. The first star catalogue, giving 1.0A0 'ft. was published by lllpparchua In hy,ar lsr, H. ('. It has ciiuia down toss through Ptolemy of Alexandria, sinrarly Sou yeara later, In 140 A. D. produced his "Megale Syntaxls " h "Almagest" of the Arabian and Mmrl.h astronnmera which, either fllrtclly or through the corrected enta- lhat was bssed on It by the Persia Per-sia astronomer, Abd-nl-rahman nl-Rut nl-Rut was the world's standard until I'liah lllelgh brought nut a new rnta-tog rnta-tog at Hamaracsnd alxint 1150 A. D. Tbi famous catalogue of Tycho llrabe -'! last of the mediaeval or the first of tits modern astronomers In U.H0, waa th, Isst Important catn'oguo pro-llurss pro-llurss without the aid of tho telescope. Hlpiiarchus and Ptolemy arrnnged the itsrs In six classes, the first clnss romtrialng the brightest about twenty twen-ty It all-while the sixth class con-talnel con-talnel those which could Just be made nut by (he naked eye. After the tele-gcotHi tele-gcotHi csme Into general use tniignl-luili tniignl-luili were extended downward as fainter stars were brought Into view by th 1i;rr,alng power of the Instrument! Instru-ment! employed. For many years each astronomer used bis own scale, llersrbel at the Capo of (liiod Hop es- OHBBUVINO KN11 OK HAltVAMU H I.AIMIKHT PIIOTOMICTKll, SI10WIN O THK HOOD FOIt THIS OIIHKFIVKH AND THK TAP.1.E AT WHICH Till! ASSISTANT TAKES DOWN THH M KASUKEMKNTS. j peclaly using very high numliera a Uudeicy thst has been so reduced since Ha tlm that his twentieth magnitude mag-nitude Is very nearly the fourteenth on the seal now generally employed. This sule more closely corresponds with tlut of Argolander, tho great flor-rnnn flor-rnnn aitbor of tha "Durrhmusterung" or catabgue of the stars lu the northern north-ern heavens, which enumerates over S'.'4,(IU0 liars, the largest number yd cataloged. Each giagnltude. of coursn, has lis typical aura to which th'i others may be conveniently refernd. The stars which do nut exactly correspond In magnitude with a typical star are ex pressed In fractional terms of tho nearest magnitudes, declmuls being usually employed, although Ptolemy and even Argelander used thirds. Em-ninvlns Em-ninvlns the decimal system, a star of 6 4 magnitude will he a shade brighter than a star of 6.6 and so ou. An exception ex-ception Is lhat certain stars, such as Arcturus and Blrius. and the planet Jupiter when at Ita brightest, are more thsn a magnitude brighter t linn atars of the first mngnltudo. Aldebar-gn, Aldebar-gn, for example, and are therefore expressed ex-pressed In "negative magnitudes," thst Is to say. they are preceded by ths minus sign. Jupiter, for Instance, approaches ap-proaches almost th second negative magnitude nilniia J or la sixteen times brighter than a star of the first magnitude. It Is significant ol tna gieat accom-pllshnisnt accom-pllshnisnt of American astronomy that there was no universally accepted system sys-tem of photometry until the publication publica-tion of what Is now known aa th Harvard photometry 1, "ji p It Is familiarly called by astronomers. This was contained n volume XIV. r,i the Annals of the Murvsrd Observn-tory, Observn-tory, under the tltlo of "Observation with the Meridian Photometer During the Years lX7ft-ls2" a inasslva volume vol-ume giving a list of 4?tin stars In the northern sky visible to th" naked eyo In the latitude of Cambridge, and In-tended In-tended to Include all stars nut fslnter than the sixth magnitude between th North Pole and thirty d 'greea south of the celestial equator. To this original list another, Voltimo XXIV. of the Annsls. tins since been added. Technically Tech-nically urh a piece of wink la called a t'ranumetrla or catnlngue of "naked-eye "naked-eye stars " The similar work produced produc-ed by Prnfensor l"rll. h,iid at Oxford, for example, containing the magnitudes magni-tudes of Z.7H4 star thus observed, waa entitled "t'rannmelrla Nova Oxonlen-ata." Oxonlen-ata." The Harvard l'ranometrla waa so elaborate and so accurately dune that It haa been practlcal'y accepted everywhere, every-where, ntid the magnitude of all new stara given on the Harvard scale. A striking Illustration of the use to which It Is now put occurred last spring when the new star appeared In the constellation Perseus. Among the observers who gav t!Hr results on the Harvard scale were Nljtand and (yl!cnskoil of Sweden. Perelra of the Portuguese observatory In the Asorcs, the stsffs of the Hrltlsh Astronomlcnl Association snd the Astronomical Society So-ciety of France and the officers of tha Itadcllffe Observatory nt Oxford, as well as prnrtlcally all American astronomers. trained eye lo notice tho finer illffer-encea illffer-encea In star magnitudes. On tho modern scale a first magnitude stnr would be expressed as ranging from 0r,0 to 1 Ml. aeeond magnitude star from 1.6(1 to I. fit), mid so on. For la-stance. la-stance. Castor, which was pleasured as 1 66 In the "II. P.." would be railed of the second magnitude, while Its twin alar, Pollux, the brighter of lbs Uemlnl, Is a first magnitude atnr, meaaured as 1.12. The Pole Star Itself Is a star of tho second magnitude, lis measurement being 2.15. The six brighter stars In the Pleiades are all nf the second and third magnitudes, as are those In tho Dipper. Tho upper slur of the two "pointers" In the Dipper that Is to say the star on the Hp opposite the ban-dlo ban-dlo haa a measurement of 1.116 In th. Harvard Photometry. The pointer be. low luis a measurement of 1 f.0, which would cany It Into tho third magnitude. magni-tude. The other bottom star of the Dipper haa a measurement of I.M, and the atar nt the Junetliui of Iho handle approaches the fourth magnitude, bav-Ing bav-Ing a measurement of only 3.41. while the star next to It draws nenr the first masnltotle, with a measurement of 1. nr.. The next slur In the Dipper, the second from the mil, Is really n double slur, but the measurement of the two together gives 2.3X. while the end star of all Is almost a typical second magnitude mag-nitude star, having a measurement of 2. U2. |