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

200'III PLATN1I'.
case she would cclipse the sun every ]new mnoon, and be herself.eclipsed every fill lmoon.
3134. l The eclipses of Jt{hpiter's satellites, in theil general
concception, are perfectly analogous to those of the Mloon, but
in thellir details they difter in several particulars. O\win to
tlle much greater distance of Jupiter from the sun, and its
gleater inagnlitude, the cone of its shadtlow is more than sixty
times that of the earth, stretelling off into space more than
55,)000000 miles. ()On tlhis account, as well cas on account of
the little inclination of their orbits to that of their plimalry, th.
three inner s-atellites of Jupiter pass tlhrougt the slhadow and
are totally eclipscd at every revolution.'lThe fourth satellite,
owsing to the grleater inclination of its orbit, sometimes, though
rarely, escapes eclilse, and sometimles merely grazes the limits
of the sfhadow, or su'llers a partial clipse.:' Tl:hese eclipses,
moreovNer, are not sent by us, as is the case with those of the
o11100io fl'Oill thte center of tlheir motion, but from a remote
station, and one whose situation, witlt respect to the line of the
shadow, is variablle. T1his of course makes no difference ill the
times of the eclipses, but a very great lifflerence in their visibility, and in theiri apl)arentl situations with respect to the
planet at the momenCllt of their entering or quitting the shadow.
335. The celipses of Jupiter's satellites present some curious
p)hllcImonenla, \whichl \Nwill be best understood fi'om a diagralm.
Let A, 113, 0 (l'ig. 65) reprlsent; the eart'; inl different palts of
its orbit, revolving fiolm A., throughl )D, to C and 13. If a line,
jouining S and A, be produced to meet the concave sphere of
of'he heavens wy, it marks the place of opposition, while the
earth is at A. flifence, Jupiter, in the figure, is reprtesenlted
east of the opl)ositioll. YWhen the earth arrives at )D, Jupitel
is int opposition; and whcll at 0, le is west of opposition..]eemlc lbelinrg nlow, tllat the satellites revolve.in the same
direction as the earth, it is obvious that when Jupiter is east of
opposition, the immersions are seen, but the emersi*ons gelnerally
take lplace behind the planet fand are not seen; so that the
ecl.pse, in this position of the bodies, always precedcs3 the
* lfcrschcl's Aist., p. 2805.