Astronomy Explained Upon Sir Isaac Newton's Principles: And made easy to those who have not studied mathematicsFerguson, James
Science
Astronomy Explained Upon Sir Isaac Newton's Principles: And made easy to those who have not studied mathematics
Ferguson, James
Astronomy -- Early works to 1800
132. So vastly great is the distance of the starry Heavens, that if
viewed from any part of the Solar System, or even many millions of miles
beyond it, its appearance would be the very same to us. The Sun and
Stars would all seem to be fixed on one concave surface, of which the
Spectator’s eye would be the centre. But the Planets, being much nearer
than the Stars, their appearances will vary considerably with the place
from which they are viewed.
133. If the spectator is at rest without their Orbits, the Planets will
seem to be at the same distance as the Stars; but continually changing
their places with respect to the Stars, and to one another: assuming
various phases of increase and decrease like the Moon. And,
notwithstanding their regular motions about the Sun, will sometimes
appear to move quicker, sometimes slower, be as often to the west as to
the east of the Sun; and at their greatest distances seem quite
stationary. The duration, extent, and points in the Heavens where these
digressions begin and end, would be more or less according to the
respective distances of the several Planets from the Sun: but in the
same Planet they would continue invariably the same at all times; like
pendulums of unequal lengths oscillating together, the shorter move
quick and go over a small space, the longer move slow and go over a
large space. If the observer is at rest within the Orbits of the
Planets, but not near the common center, their apparent motions will be
irregular, but less so than in the former case. Each of the several
Planets will appear bigger and less by turns, as they approach nearer or
recede farther from the observer; the nearest varying most in their
size. They will also move quicker or slower with regard to the fixed
Stars, but will never be retrograde or stationary.
134. Next, let a spectator in motion view the Heavens: the same apparent
irregularities will be observed, but with some variation resulting from
his own motion. If he is on a Planet which has a rotation on it’s Axis,
not being sensible of his own motion he will imagine the whole Heavens,
Sun, Planets, and Stars to revolve about him in the same time that his
Planet turns round, but the contrary way; and will not be easily
convinced of the deception. If his Planet moves round the Sun, the same
irregularities and aspects as above will appear in the motions of the
Planets: only, the times of their being direct, stationary and
retrograde will be accelerated or retarded as they concur with, or are
contrary to his motion: and the Sun will seem to move among the fixed
Stars or Signs, directly opposite to those in which his Planet moves;
changing it’s place every day as he does. In a word, whether our
observer be in motion or at rest, whether within or without the Orbits
of the Planets, their motions will seem irregular, intricate and
perplexed, unless he is in the center of the System; and from thence,
the most beautiful order and harmony will be observed.
Public-domain text, read in full here on John Shaqi.
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