Page 584 - 89 history of astronomy_opt

ˆ
ˆ
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pus, I l Orionis, I l Cygni, I Centauri, and I ˆ
Cassiopeia. Oudemans has published a list
of parallaxes observed.[4]
Proper Motion. –In 1718 Halley[5] de-
tected the proper motions of Arcturus and
Sirius. In 1738 J. Cassinis[6] showed that
the former had moved five minutes of arc
since Tycho Brahe fixed its position. In
1792 Piazzi noted the motion of 61 Cygni
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