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the equation of the centre. But Copernicus
remarked that he could also use an epicycle
for this purpose, or that he could use both
an excentric and an epicycle for each planet,
and so bring theory still closer into accord
with observation. And this he proceeded to
do.[6] Moreover, observers had found irreg-
ularities in the moon’s motion, due, as we
now know, to the disturbing attraction of
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