Cassiopeia is a "W"- shaped
constellation almost directly overhead and slightly north in December
soon after sunset. Cassiopeia is an interesting constellation for
several reasons.
1. It's Circumpolar:
It's one of a few constellations that never rise and never set.
They just (appear to) go in circles around the North Star -- every
day a circle, and every year a much slower circle. At 6AM tomorrow
it will be low in the sky to the north, and 6 months from now in the
evening, it will be about the same place.
If
you lived at the North Pole, all the stars you could see would be
circumpolar. But they'd only be half the stars in the sky, because
the other half -- which you would never see -- would be circumpolar
for those penguins looking up from the South Pole.
2. It's always opposite the Big
Dipper,
with the North Star about midway between them. So, if you look north
from Cassiopeia, and keep going north and lower in the sky, you'll
find the Big Dipper low in the north. 3 months ago and 3 months from
now, they were opposite each other east to west.
3. The band of the Milky Way
goes through it.
We're in the Milky Way galaxy, which is shaped like a disk. When we
see it as a fuzzy band of many, many stars, we're looking along the
plane of the disk, so we see what looks like a band of stars. When
we look anywhere except along this plane we just see a few stars that
are close, and that's what the rest of the sky (outside the band) looks like.
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