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

PART II.- -— OF T E11 I SOtLAR SYSTEM.............................. r
1 42. IITAvINo cosidered tlihe IPartlh, in its astronomical relatio(s, and(l the Doctrinlte of the Sphere, we proceed now to a
survey of the Solar Sylstem, and shall treat succ essively of thoe
Sun, M1oonll, P tlanets, and Comets.
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1 43. I.ntn fiqtrle whichl the sun presents to uts is tihat of a
perfect circle, whereas most of the planets exittllit a disk morel
or less cliiptical, indicating that the trite shape of the body is
an. oblate spheroid. So great, hlowever, is tlhe distance of the
sun, fthat a line 400 miles long wvould sultd s te angle of only
I" at thte eve, lanrd w\ould, therefore, be the least space that
could bc:measured. 1 eItce, were the differetilce betweenll two
conljugate diameters of thle sull any quantity less thaln t1is, we
could not deternine by actual measurement that it existed at:
all, Still we learn from teoretlOtical conXsi erations, founded
upon the known effects of centrifugallt l force, arising from the
sunl's rexvolution on hlls axis, tlhat his figure is not a )erfect
)lcphere, but is slighlltly splheroidal."t'
144. The dista.tnce qf t/te sutn f;rom. the eaHrtA is nearly
95,000,000 miles. Ft?'or, its horizontal patiatlltsx being 8"J6
(Art. 86), and the semi-diamneter of thle eartht 3956 miles,
Sin 8".6: 3956:tad: 95,000,000 ncarly.
In order to formln somer faint conception at least of this vast
distance, let us reflect that a railway car, moving at tde rate of
20 miles per hIour, would require mlore than.500 years to reace
th1e sutl.
o See Mdtcanique Ctcstec, iii., p. 165. 1)elambre, t. i., p. 483.