332. The Moon’s Orbit being elliptical, and the Earth in one of its
focuses, she is once at her least distance from the Earth, and once at
her greatest in every Lunation. When the Moon changes at her least
distance from the Earth, and so near the Node that her dark shadow falls
on the Earth, she appears big enough to cover the whole [75]Disc of the
Sun from that part on which her shadow falls; and the Sun appears
totally eclipsed there, as at _A_, for some minutes: But when the Moon
changes at her greatest distance from the Earth, and so near the Node
that her dark shadow is directed towards the Earth, her diameter
subtends a less angle than the Sun’s; and therefore she cannot hide his
whole Disc from any part of the Earth, nor does her shadow reach it at
that time; and to the place over which the point of her shadow hangs,
the Eclipse is annular as at _B_; the Sun’s edge appearing like a
luminous ring all around the body of the Moon. When the Change happens
within 17 degrees of the Node, and the Moon at her mean distance from
the Earth, the point of her shadow just touches the Earth, and she
eclipseth the Sun totally to that small spot whereon her shadow falls;
but the darkness is not of a moment’s continuance.
[Sidenote: The longest duration of total Eclipses of the Sun.]
333. The Moon’s apparent diameter when largest exceeds the Sun’s when
least only 1 minute 38 seconds of a degree: And in the greatest Eclipse
of the Sun that can happen at any time and place, the total darkness
continues no longer than whilst the Moon is going 1 minute 38 seconds
from the Sun in her Orbit; which is about 3 minutes and 13 seconds of an
hour.
[Sidenote: To how much of the Earth the Sun may be totally or partially
eclipsed at once.]
334. The Moon’s dark shadow covers only a spot on the Earth’s surface,
about 180 _English_ miles broad, when the Moon’s diameter appears
largest and the Sun’s least; and the total darkness can extend no
farther than the dark shadow covers. Yet the Moon’s partial Shadow or
Penumbra may then cover a circular space 4900 miles in diameter, within
all which the Sun is more or less eclipsed as the places are less or
more distant from the Center of the Penumbra. When the Moon changes
exactly in the Node, the Penumbra is circular on the Earth at the middle
of the general Eclipse; because at that time it falls perpendicularly on
the Earth’s surface: But at every other moment it falls obliquely, and
will therefore be elliptical; and the more so, as the time is longer
before or after the middle of the general Eclipse; and then, much
greater portions of the Earth’s surface are involved in the Penumbra.
[Sidenote: Duration of general and particular Eclipses.
The Moon’s dark shadow.