The passage of the moon behind and in front of the
earth, and its eclipses when it goes into the earth's shadow, could be
seen without the aid of telescopes, while, with such instruments, these
phenomena would possess the highest scientific interest and importance.
Because the earth has a satellite so easily observable, the astronomers
of Venus could not remain ignorant of the exact mass of our planet, and
in that respect they would outstrip us in the race for knowledge, since,
on account of the lack of a satellite attending Venus, we have been able
to do no more than make an approximate estimate of her mass.
With telescopes, too, in the case of a solar eclipse occurring at the
time of the earth's opposition, they could see the black spot formed by
the shadow of the moon, where the end of its cone moved across the earth
like the point of an invisible pencil, and could watch it traversing
continents and oceans, or thrown out in bold contrast upon the white
background of a great area of clouds. Indeed, the phenomena which our
globe and its satellite present to Venus must be so varied and wonderful
that one might well wish to visit that planet merely for the sake of
beholding them.
Thus far we have found so much of brilliant promise in the earth's twin
sister that I almost hesitate to approach another phase of the subject
which may tend to weaken the faith of some readers in the habitability
of Venus.
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