348. When the Moon is Full at 12 degrees from either of her Nodes, she
just touches the Earth’s shadow but enters not into it. Let _GH_ be the
Ecliptic, _ef_ the Moon’s Orbit where she is 12 degrees from the Node at
her Full; _cd_ her Orbit where she is 6 degrees from the Node, _ab_ her
Orbit where she is Full in the Node, _AB_ the Earth’s shadow, and _M_
the Moon. When the Moon describes the line _ef_ she just touches the
shadow but does not enter into it; when she describes the line _cd_ she
is totally though not centrally immersed in the shadow; and when she
describes the line _ab_ she passes by the Node at _M_ in the center of
the shadow, and takes the longest line possible, which is a diameter,
through it: and such an Eclipse being both total and central is of the
longest duration, namely, 3 hours 57 minutes 6 seconds from the
beginning to the end, if the Moon be at her greatest distance from the
Earth: and 3 hours 37 minutes 26 seconds, if she be at her least
distance. The reason of this difference is, that when the Moon is
farthest from the Earth she moves slowest; and when nearest to it,
quickest.
[Sidenote: Digits.]
349. The Moon’s diameter, as well as the Sun’s, is supposed to be
divided into twelve equal parts called _Digits_; and so many of these
parts as are darkened by the Earth’s shadow, so many Digits is the Moon
eclipsed. All that the Moon is eclipsed above 12 Digits, shew how far
the shadow of the Earth is over the body of the Moon, on that edge to
which she is nearest at the middle of the Eclipse.
[Sidenote: Why the beginning and end of a lunar Eclipse is so difficult
to be determined by observation.]
350. It is difficult to observe exactly either the beginning or ending
of a lunar Eclipse, even with a good Telescope; because the Earth’s
shadow is so faint, and ill defined about the edges, that when the Moon
is either just touching or leaving it, the obscuration of her limb is
scarce sensible; and therefore the nicest observers can hardly be
certain to four or five seconds of time. But both the beginning and
ending of solar Eclipses are visibly instantaneous; for the moment that
the edge of the Moon’s Disc touches the Sun’s, his roundness seems a
little broke on that part; and the moment she leaves it he appears
perfectly round again.
[Sidenote: The use of Eclipses in Astronomy, Geography, and Chronology.]
351. In Astronomy, Eclipses of the Moon are of great use for
ascertaining the periods of her motions; especially such Eclipses as are
observed to be alike in all circumstances, and have long intervals of
time between them. In Geography, the Longitudes of places are found by
Eclipses, as already shewn in the eleventh chapter: but for this purpose
Eclipses of the Moon are more useful than those of the Sun, because they
are more frequently visible, and the same lunar Eclipse is of equal
largeness and duration at all places where it is seen. In Chronology,
both solar and lunar Eclipses serve to determine exactly the time of any
past event: for there are so many particulars observable in every
Eclipse, with respect to its quantity, the places where it is visible
(if of the Sun) and the time of the day or night; that ’tis impossible
there can be two Eclipses in the course of many ages which are alike in
all circumstances.
[Sidenote: The darkness at our SAVIOUR’s crucifixion supernatural.]
352. From the above explanation of the doctrine of Eclipses it is
evident, that the darkness at our SAVIOUR’s crucifixion was
supernatural. For he suffered on the next day after eating his last
Passover-Supper, on which day it was impossible that the Moon’s shadow
could fall on the Earth, for the _Jews_ kept the Passover at the time of
Full Moon: nor does the darkness in total Eclipses of the Sun last four
minutes in any place § 333, whereas the darkness at the crucifixion
lasted three hours, _Matt._ xxviii. 15. and overspread at least all the
land of _Judea_.