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Cassiopeia

Still Image (Now)
Animation (24,000 Years)

Cassiopeia contains two rapidly-moving naked-eye stars, Eta Cassiopeiae and Mu Cassiopeiae. Mu Cassiopeiae is one of the most rapidly-moving naked-eye stars, and, in fact, belongs to a different class of stars than most stars visible from Earth. It is a member of Population II, a group of stars with large, highly eccentric orbits around the Galaxy. Unlike the Sun, which will always remain more-or-less in the plane of the Milky Way Galaxy, Mu Cassiopeia moves above and below the plane of the galaxy by thousands of light years. Because of this unusual orbit, Mu Cassiopeia and other Population II stars seem to move very quickly with respect to the Sun.

Midway through the animation, i.e., after about 12,000 years, the very nearby and fast-moving star 61 Cygni barrels into Andromeda, the constellation just south of (below) Cassiopeia. By the end of the animation, 61 Cygni has passed through Cygnus, Andromeda, and Cassiopeia itself, en route to Perseus (the constellation at the extreme left of the chart).

Somewhat farther away than these three stars, but still relatively close to the Sun, is Beta Cassiopeiae, the rightmost star in the "W". Midway through the animation, Beta moves enough to distort the familiar shape; after 50,000 years, longer than the scope of this animation, Cassiopeia would be largely unrecognizable.

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