Page 504 - 89 history of astronomy_opt

Twenty-four hours is probably about the
period of rotation for each of these planets.
Several observers have claimed to have
seen a planet within the orbit of Mercury,
either in transit over the sun’s surface or
during an eclipse. It has even been named
Vulcan . These announcements would have
received little attention but for the fact that
the motion of Mercury has irregularities which
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