times behind us, sometimes at a right
angle in relation to the Sun and the Earth. Now, the eclipses of the Sun
occur invariably at the time of New Moon, when our satellite passes
between the Sun and ourselves, and the eclipses of the Moon, at the
moment of Full Moon, when the latter is opposite to the Sun, and behind
us.

This fact soon enabled the astronomers of antiquity to discover the
causes to which eclipses are due.

The Moon, passing at the beginning of its revolution between the Sun and
the Earth, may conceal a greater or lesser portion of the orb of day. In
this case there is an eclipse of the Sun. On the other hand, when it is
on the other side of the Earth in relation to the Sun, at the moment of
Full Moon, our planet may intercept the solar rays, and prevent them
from reaching our satellite. The Moon is plunged into _the shadow of the
Earth_, and is then eclipsed. Such is the very simple explanation of the
phenomenon. But why is there not an eclipse of the Sun at each New Moon,
and an eclipse of the Moon at each Full Moon?

If the Moon revolved round us in the same plane as the Earth round the
Sun, it would eclipse the Sun at each New Moon, and would be itself
eclipsed in our shadow at each Full Moon. But the plane of the lunar
orbit dips a little upon the plane of the terrestrial orbit, and the
eclipses can only be produced when the New Moon or the Full Moon occur
at the line of intersection of these two planes, _i.e._, when the Sun,
the Moon, and the Earth are upon the same straight line. In the majority
of cases, instead of interposing itself directly in front of the
sovereign of our system, our satellite passes a little above or a little
below him, just as its passage behind us is nearly always effected a
little above or below the cone of shadow that accompanies our planet,
opposite the Sun.

When the Moon intervenes directly in front of the Sun, she arrests the
light of the radiant orb, and conceals a greater or less portion of the
solar disk. The eclipse is partial if the Moon covers only a portion of
the Sun; total if she covers it entirely; annular, if the solar disk is
visible all round the lunar disk, as appears when the Moon, in her
elliptical orbit, is beyond medium distance, toward the apogee.

On the other hand, when the Moon arrives immediately within the cone of
shadow that the Earth projects behind it, it is her turn to be eclipsed.
She no longer receives the rays of the Sun, and this d