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

I.t s 6 THflE: PJi JANEITS,
noine at all. It will aid tle memory, and render our view of
the planoetary system more clear and comprehlensive, if we
classify, as fnar as possible, the various particulars conlprelendedt under the foregoing headnfs.
299. )ISTANOESl lt RJolE, SUiN.:*<'
1. Mercury, 3Y,000,000 0.3870981
2.'Velnus, 68,)000,000 0.723331.6
3. E arth, 9, )000,000 1.0000000
4..Atars, 14-5,000,000:1.-5236923
5. 9l'lanetoids, 250,000,000.661t2885
6. Jupiter, 495,000,000 56.2027760
7. Saturn, 900,000,000 9.5387861
8. Ufranus, 1,800,O00,000 19.1823900
9..Neptuiec, 2,800,000,000 30.0318000
ltt h i d7imel2sions of the planetary systelm are seen fhrom this
table to be vast, comprehelnding a circular space nearly six
thousand millions of miles in liamlleter. A rail\way ear, trayelingl nglht and day at the rate of 20 miles an hour, and of
course making 480 miles a day, Nwould require about 50 d(lays
to travel round the Earth on a. great circle, and labout 500 days
to reach the moon; but it \will,ive some idea of tihe \vastness
of the planetary spaccs to reflect, that setting out from tle
sun:, and travelilng fiom planelt to panllct at the same rate, to
reacl M:tercury w\ould require about 200 years; V'cnus, tlcarly
400; the Earth, 542; IMars, more than 800; Jupiter, toward
3,000; Satutrn, above 5,000; Uranus, 10,000; N-cpttune, more
than.16,000; and to cross the enltire orbit of ]Neptune would
require upwaard of 32,000 years.
It Imay aid the lmen ory to remark, that in regard to tlhe
planets nearest the sun, the distalncees increase inl anl arithmetical ratio, while thlose most remote increase in a geometllrical
ratio. Tltulls, if we\ add 30 to the distance of:tercury, it gives
ius Inearly that of Venus; 30 more gives thlat of tlhe Earth
while Saturn i's nearly twice the distance of Jupitel, andl
0'111e distances in miles, as expressed ill tho first. olumnll, are to be treasured
lup in tile mermfory, while the secondl column0tl expresses thie rdative distance, that
of thce arth bcing 1, fromt wNhich a more exact determination may be lmade
when requiredl, the Earth's (listance being taken at 9'5,2'8,260 mliles.