62. The Moon’s Axis is so nearly perpendicular to the Ecliptic, that the
Sun never removes sensibly from her Equator: and the[14] obliquity of
her Orbit, which is next to nothing as seen from the Sun, cannot cause
any sensible declination of the Sun from her Equator. Yet her
inhabitants are not destitute of means for determining the length of
their year, though their method and ours must differ. For we can know
the length of our year by the return of our Equinoxes; but the
Lunarians, having always equal day and night, must have recourse to
another method; and we may suppose, they measure their year by observing
the Poles of our Earth; as one always begins to be enlightened, and the
other disappears, at our Equinoxes; they being conveniently situated for
observing great tracks of land about our Earth’s Poles, which are
entirely unknown to us. Hence we may conclude, that the year is of the
same absolute length both to the Earth and Moon, though very different
as to the number of days: we having 365-1/4 natural days, and the
Lunarians only 12-7/19; every day and night in the Moon being as long as
29-1/2 on the Earth.
[Sidenote: And the longitudes of their places.]
63. The Moon’s inhabitants on the side next the Earth may as easily find
the longitude of their places as we can find the latitude of ours. For
the Earth keeping constantly, or very nearly so, over one Meridian of
the Moon, the east or west distances of places from that Meridian are as
easily found, as we can find our distance from the Equator by the
Altitude of our celestial Poles.
[Sidenote: Mars.