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

JUlPI'l'. 1)'J
wlicl wl, observe tChem fi'om thle eartl'.'ltheir otion is altelrnately direct and retrotgrade; they are soIinetile-s stationary;
(tld, ill shlort, tthey exhibit ill miniature all the phllenonmeva of
tile planetary system. V'alrious particulars of tho System are
ex]hibitcd in tht foillowing table, the diameters being ill miles,
tand tile distalnces beilng t ikcl fiotll the celtl of tlle prilllmy.'':'
ate11ito". )ialeter, 31stl e&s. Sidereal levolition. i
t 2,it44 0 1 278,500 l Id. 1 8h. 28,n.
2 2,190 44,13,300 3 13 15
3 3,580 707,000 7 3 43
4 3,000 1, 243),500 6 16:32
Fron this table we see that Julpiter's satellites are all larger
than the oon, tlhe second exceeding it by only 30) miles in diameter, tlhe third by 11420 miles.'The third, the largest of the
whole, has still only *.J2th the diamleter of the primary.'rThe
gre'ater distalnces also of these moons compared w\tit.h ours,
rclduccs theirl al)paret size andl lightl as seI fi'om Jupiter.
Tlhus t1he larpgest of thelm would exhlibit to a specctator oil tle
equator of tle planlct, a diameter of only 36', whlicll is only a
little gretater thanl that of thle mlOOi, w hile tle smallest wonuld
applear only one-fourth as large. It is nloticeablle, thltat thle
satellites of Jupiter mIakie veryt quick revolutionls, wlli cotm)ar'ed w ith tile earth's moo001n althoughl telly are all at greater
distances friom tile primary than tie moon from the earthl; thle
fullrthest revolving in about -A of the 1moon's p)eriod(, and the
ncarest more tlhan 16 times as quick. Tltis is because they are
so powerfilly attracted by t}le 1)lanet. To 1)revent tlheir bjijig
drawn inl from their circular O'rbits, a great projectile velocity is
333. T'l orbits of tl1e satellites are nearly or quite ciruelar, and( (leviate but little firom tihe llaile of the )planct's
cquator, and of courso arc but slightly inclined to the plane of
Ilis orbit. TheI'y are, therefore, in a similar sitlationl witlh
respect to Jupiter as tlhe 11100o1 would be w ith lrSl)eet to th}o
earthl, if her orbi)t nearly coincided wvith the ecliptic, in whlliel1..................... -...............................................