An introduction to astronomy: designed as a text-book for the use of students in college. By Denison Olmsted ...

PAnRT III. —-— O TillE' FIXlDI) STAllRS AND SYSTEM OF Tl'Illl
WORLL).
-0......A.. -. —........
a I1:A;.> A'1 "T R[ I.
OJ' TI fI'l XU1EJ) fSTARS C.......ON..ST1T,LIATI'IONS.
410. Tllll" FiI'Xlu) STARs are so called, b1eeause, to common
observation, thely always maintain the same situations with re —
spect to one another.
JtIlie stars are classed by their apparent magi titlde~S. The
whole number of magnitudes recorded are si:cteei, of whichl thle
first six only arle visible to the naked eye; tlhe rest are tdlescoljpi
sl/a/s.. As the stars w]hicl are now grouped together underlill one
of the first six m-gnitudles are very unequal among tlhemselves,
it has rccently been prol)oscd( to subdivide eacll class into tihlree,
makling ill - igh teen instead of six magnitudes visible to the
nakedl eve. tihese magiitudes alre not determined 1)by any
ver'y defillit:e scale, but are mer ely ranked according to their
relattivc d(egrees of brightness, and this is left ill a great nieasurc to tlhe lecision of the eye ahnlle, althloutgh it'would appear
easy to measure the compairative degree of light in a star by a
photomete-, and upon suc(h mneasurement to grounld a more
scientific classification of tihe stars. The brigtest stars to the
ilnumberl of I. or 20 are considlered as stars of th~e first mllagni..
tude; thle 50 or 60 next brigltest, of tlle secod mlf'nitlde;
the next 200 of tile thinrd matognitlde; and th1us tlhe number of
each clfass illcreases r1apidly as we deseend the scale, so tlhat no
less than fifteen o1l twellty tllussand are included within the
first seveni magiS itutc(s.
4 1 1.'l'le stars hlave been grouped in C(onstell/tions from
the most remote antiquity; a fevw, as Orion, IBootes, and'Ursa
iMaior, a're mteinetionldt ill the m iost ancient \wrlitings un(ler the
same namles asl they bear' at plresent. lThe names of thle con