Lecture #36: Uranus, Neptune, and Pluto
I. Uranus
-- discovered by William Herschel in 1781.
-- Herschel was originally a musician but became
one of the most famous astronomers ever because of this meticulous surveys
of the sky with fine telescopes.
-- Herschel was not looking for a planet, we was looking for two stars which
coincidentally looked close together even though one was much closer. If
he could find that, he could see the parallax due to Earth's orbit, which
still had never been seen.
-- Herschel did succeed in finding a large number of stars that looked very
close together, but never saw parallax. Why not, and what do you think
he ended up discovering instead?
II. Neptune
-- Neptune was detected by looking at its gravitational effects on Uranus,
and calculating where it should be. A triumph of theory!
III. Pluto
-- Percival Lowell thought there were problems with Neptune's orbit too, and
calculated where a ninth planet would have to be.
-- It was found by Tombaugh, but was just chance-- Lowell's calculation was
not correct because Neptune's orbit was actually not affected by Pluto!
-- Still, PL are Lowell's initials, and begin the name Pluto.