"A moment's reflection must tell you," replied Barbican, "that when we
started last night, the Sun was almost directly below us; therefore, as
we continue to move in a straight line, he must still be in our rear."
"That's clear enough," said the Captain, "but another consideration, I'm
free to say, rather perplexes me. Since our Earth lies between us and
the Sun, why don't we see the sunlight forming a great ring around the
globe, in other words, instead of the full Sun that we plainly see there
below, why do we not witness an annular eclipse?"
"Your cool, clear head has not yet quite recovered from the shock, my
dear Captain;" replied Barbican, with a smile. "For two reasons we can't
see the ring eclipse: on account of the angle the Moon's orbit makes
with the Earth, the three bodies are not at present in a direct line;
we, therefore, see the Sun a little to the west of the earth; secondly,
even if they were exactly in a straight line, we should still be far
from the point whence an annular eclipse would be visible."
"That's true," said Ardan; "the cone of the Earth's shadow must extend
far beyond the Moon."
"Nearly four times as far," said Barbican; "still, as the Moon's orbit
and the Earth's do not lie in exactly the same plane, a Lunar eclipse
can occur only when the nodes coincide with the period of the Full Moon,
which is generally twice, never more than three times in a year.
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