_Of Eclipses: Their Number and Periods. A large Catalogue of Ancient and
Modern Eclipses._
[Sidenote: A shadow, what.]
312. Every Planet and Satellite is illuminated by the Sun; and casts a
shadow towards that point of the Heavens which is opposite to the Sun.
This shadow is nothing but a privation of light in the space hid from
the Sun by the opake body that intercepts his rays.
[Sidenote: Eclipses of the Sun and Moon, what.]
313. When the Sun’s light is so intercepted by the Moon, that to any
place of the Earth the Sun appears partly or wholly covered, he is said
to undergo an Eclipse; though properly speaking, ’tis only an Eclipse of
that part of the Earth where the Moon’s shadow or [64]Penumbra falls.
When the Earth comes between the Sun and Moon, the Moon falls into the
Earth’s shadow; and having no light of her own, she suffers a real
Eclipse from the interception of the Sun’s rays. When the Sun is
eclipsed to us, the Moon’s Inhabitants on the side next the Earth (if
any such there be) see her shadow like a dark spot travelling over the
Earth, about twice as fast as its equatoreal parts move, and the same
way as they move. When the Moon is in an Eclipse, the Sun appears
eclipsed to her, total to all those parts on which the Earth’s shadow
falls, and of as long continuance as they are in the shadow.
[Illustration: Plate X.
_J. Ferguson delin._ _J. Mynde Sculp._]
[Sidenote: A proof that the Earth and Moon are globular bodies.]
314. That the Earth is spherical (for the hills take off no more from
the roundness of the Earth, than grains of dust do from the roundness of
a common Globe) is evident from the figure of its shadow on the Moon;
which is always bounded by a circular line, although the Earth is
incessantly turning its different sides to the Moon, and very seldom
shews the same side to her in different Eclipses, because they seldom
happen at the same hours. Were the Earth shaped like a round flat plate,
its shadow would only be circular when either of its sides directly
faced the Moon; and more or less elliptical as the Earth happened to be
turned more or less obliquely towards the Moon when she is eclipsed. The
Moon’s different Phases prove her to be round § 254; for, as she keeps
still the same side towards the earth, if that side were flat, as it
appears to be, she would never be visible from the third Quarter to the
first; and from the first Quarter to the third, she would appear as
round as when we say she is Full: because at the end of her first
Quarter the Sun’s light would come as suddenly on all her side next the
Earth, as it does on a flat wall, and go off as abruptly at the end of
her third Quarter.
[Sidenote: And that the Sun is much bigger than the Earth, and the Moon
much less.]
315. If the Earth and Sun were equally big, the Earth’s shadow would be
infinitely extended, and all of the same breadth; and the Planet Mars,
in either of its nodes and opposite to the Sun, would be eclipsed in the
Earth’s shadow. Were the Earth bigger than the Sun, it’s shadow would
increase in breadth the farther it was extended, and would eclipse the
great Planets Jupiter and Saturn, with all their Moons, when they were
opposite to the Sun. But as Mars in opposition never falls into the
Earth’s shadow, although he is not then above 42 millions of miles from
the Earth, ’tis plain that the Earth is much less than the Sun; for
otherwise it’s shadow could not end in a point at so small a distance.
If the Sun and Moon were equally big, the Moon’s shadow would go on to
the Earth with an equal breadth, and cover a portion of the Earth’s
surface more than 2000 miles broad, even if it fell directly against the
Earth’s center, as seen from the Moon: and much more if it fell
obliquely on the Earth: but the Moon’s shadow is seldom 150 miles broad
at the Earth, unless when it falls very obliquely on the Earth, in total
Eclipses of the Sun. In annular Eclipses, the Moon’s real shadow ends in
a point at some distance from the Earth. The Moon’s small distance from
the Earth, and the shortness of her shadow, prove her to be less than
the Sun. And, as the Earth’s shadow is large enough to cover the Moon,
if her diameter was three times as large as it is (which is evident from
her long continuance in the shadow when she goes through it’s center)
’tis plain, that the Earth is much bigger than the Moon.
[Sidenote: The primary Planets never eclipse one another.