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

ASTIRONOMI\CAL PI'ItIOBLEM5. 6t
Let PIOCP' (Fig. 20) represent the celestial melridian thlat
ptasses through tlhe first of Caneer and Capricorn (tlle solstitial
colure), V.P'' the axis of the spllere, EIQ thle eqtuator,.IC' the
ecliptic, and -PSI"' the declination
circle (Art. 37) passing through the ig. 20.
sun S; tlhel ARlS is a right angle,..............
and in the right-angled sp>herical
triangle AI NS, are given thle right /
tasclnsion AIt (.Art.'37), and the dec- A1
lination ES, to find the lonrgitudte -/.IAS and tle ob1liquity SAIL. (q
As longtitude and right ascension
are measured friom A, the first point
of Aries, in the direction AS of the,signs, quite round the globe, when, of the four quantities mentioned in the problem, the obliqutity and the declination are
given to find the others, w\e miust know wlethller tle sunl iS
north, or Nwhetther it is south of the equator, the longitude
being in the one case AS, and ini the othler, instead of AS', it
is 360... AS', when near the same quiilitox, A. ~We nlust also
knaow on which side of the tropic the sunll is, for the sun in
passiltg from one of thle tropics to the equilnox, passes thllrougt
the same degrees of tleclination as it had gone throughl in ascendling from the other equinox to the tropic, atlthoulgh its
lolgitude and riglht ascension go on continuatlly increasingl.'1romn the 21st of M:tarch to tile 21st of Jlune, whlile (leseriibilg
t-he first quadrant firom the vernal equinlox, the declintation is
north and increasin g; north, but decreasing, in the second
quadrant, until tlhe 238d of September; southt and increasing
in tle tltird quad(rant, until the 21st of Decemberl; and fintally,
il the folurth quadrant, south but decreasing until thle 21st of
March..EX. 1. Oin the L1th of M:ay, thfe sun's':Riglht. Ascension Nwas
530 38', and his D)eclination 19 15.' 57"' r:equired ltis L]ongitudo
and the Obliquity of the Ecliptic.
Applying N-apier's Rtule*& to thle right-angled triangle ARS,
we have
* The studenlt is supp)RoseCd to be acquallinted ith Spherical'ltigononmetry; but
to refresh his memory, we may insert: a remark or two.