The gigantic character of the lunar features impresses the
beholder not less than the universality of the play of destructive
forces which they attest. Let us make a few comparisons. Take the
lunar crater called ``Tycho'', which is a typical example of its kind.
In the telescope Tycho appears as a perfect ring surrounding a
circular depression, in the center of which rises a group of
mountains. Its superficial resemblance to some terrestrial volcanic
craters is very striking. Vesuvius, seen from a point vertically
above, would no doubt look something like that (the resemblance would
have been greater when the Monte del Cavallo formed a more complete
circuit about the crater cone). But compare the dimensions. The
remains of the outer crater ring of Vesuvius are perhaps half a mile
in diameter, while the active crater itself is only two or three
hundred feet across at the most; Tycho has a diameter of fifty-four
miles! The group of relatively insignificant peaks in the center of
the crater floor of Tycho is far more massive than the entire mountain
that we call Vesuvius. The largest known volcanic crater on the earth,
Aso San, in Japan, has a diameter of seven miles; it would take sixty
craters like Aso San to equal Tycho in area! And Tycho, though one of
the most perfect, is by no means the largest crater on the moon.
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