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

sANrURN. 209
ftom the sun as thle earnth is, therefore, 9.54: 1: 81: SE"
rad ~ sin 813E; whllich is thus found to be 6~ 1'. lenee, f13St.-z=G~ 1', and BI13) D.:192 2'. B3ut Saturn describes:1.2 2' ill 3o.9
days, nlellr six days less than a year. The carte therefore vel)ry
nearly describes the orbit ]F.,GlI, while Satull'n describes tho
arce B))D.
346:. The disappearances of the ring maay be variously
modified during the year of ptssing the iode, according to the
place of the earth whlen the nodal line first reaches its orbit..A few cfases are here described.'If the carth is at G, whetl the
planc of tlhe ring passes iE, then, whlile the nodal line moves
from ll ]BE to CS, tile earth will go from 0G througl l il to ZE, anlld
must cross tlhat line below 1t. thle ring will berin its disappearance at tlhat moment; but the disaplpelarance wvill contite,
as the earth proceeds to EI, beccause thle lark side is toward it.'ThIlis disaplearanle Awill last about two mont.hls, and close wllhen
the plane of the ring at 0 passes the slun; for after that, thle
illumin.a-fted side will be to toward the earth. While the earth
pr'oceeds fro1m 1 thirough 1' to (G, the l)lane of tihe ring' \will
love fr'om CS to 1)C} before the eartlh can overtake it.
Again, if thle eath had fadvmeIed some distance oil tltl
quadramt (Gl, when tle rillg's line of no1des was at E]!, then
they will meet fuirther from 1. tlhan before, say at. [; aftoer
which thle (lark side will be toward tihe earth. Thle plane of
the ring will lpass tlhe sun, whln the earth is on thle quadrant
El, after whicll the brighlt side is lrcseltled to thle earth.. But
tihe carth ltill overtake the nodal line before reatlillng G, and
thlerefore look again upon the dark side, until it rcerosses the
line on thtl qualdraltlt GJ-I. T.ihus there are two periodts of disappelrance. Thlcse two mlay possibly ulite inl one, of 8
monthll s' continuance; this will llappenl wlhen thie earth and
node-line lass f' at the same time; for then the plane of thlle
ring is b)etween the earth and suntt both before and after passing throughl tlhe sun.
It is a possible tl g thin, that no disappearatnce at all should
a)ppen dlurling tllh nodal year. Suppose the earthll at'F, w11l
tlet line of noldes arrives at 1:. T}hlnl, wllile tillnc mtoves
fiom [)BEt to CS, the earth will desciribe F'IlG, all thle time on
tle luminous sidle of the llring; tell earth and sun wvill botlh l)t
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