Circumpolar Stars in the Night Sky

Constellation Cassiopeia
Constellation Cassiopeia

I don’t know what it is, but winter makes me look up. When I arrive home after dark, I often find myself looking up at a clear, cold night sky. The stars always seem more sparkling and brilliant in the winter sky. And a night sky seems clearer.

When I was in junior high, I used to sit on my front steps, with a star map in hand, and pick out all the constellations. I had a very simple book of star maps for each month. I wish I still had that book, but it disappeared somehow.

After weeks of looking in a cold night sky, I offer this information on star-gazing. As always I focus on the basics you need to know to amaze your friends and yourself with your natural history knowledge.

Circumpolar is Latin for “around the pole”.  Circumpolar stars are any stars that appear to circle around the Earth’s north or south poles.  Each “pole” or hemisphere has its own set of constellations. These constellations always appear in the sky. They never sink below the horizon. They can be seen no matter what the season.

North Pole – the Northern Hemisphere

The northern hemisphere’s constellations circle around the North pole. The North Star is almost directly over the North Pole. Therefore, the northern circumpolar stars seem to circle the North star.

In the Northern Hemisphere, there are only 6 such constellations (above lat. 40 degrees N). The designation of 40 degrees north latitude passes through Philadelphia, Columbus, Ohio, and just south of the northern California border.  The constellations are:

  • Ursa Minor  (the Little Dipper or the Lesser Bear)
  • Ursa Major (the Big Dipper or the Great Bear)
  • Cassiopeia (the Lady in the Chair – the constellation shaped like a “W”
  • Cepheus (the King)
  • Draco (the Dragon)
  • Camelopardalis

Just six? That’s right just six.

And FYI:

South Pole – the Southern Hemisphere

Southern hemisphere constellations don’t circle around a star, because there is no “south star’. The point where it would be if it existed is called the South Celestial Pole. The longest axis of the constellation Crux, the Southern Cross points almost directly to the spot where the “south star” would be if it existed.
In the Southern Hemisphere, there are 11 constellations which circle the south celestial pole. They tend to be smaller than their northern counterparts, so there are more of them.  The constellations are:

  • Toucan
  • Southern Cross
  • Octans
  • Apus
  • Triangulum Australe
  • Musca, Chameleon
  • Volans
  • Mensa
  • Reticulum
  • Hydrus
  • Pavo

By knowing the circumpolar stars you will know the main constellations. Then it will be easier to pick out the new ones as the seasons change. A star chart is a map of the night sky. Very simple ones show the biggest, brightest stars. More complex charts show hundreds of stars and celestial bodies.

Star maps are available in astronomy magazines.  Sky and Telescope has a weekly “sky-at-a-glance” feature on its website.  This same website has many beginning star-gazing how-to’s.

Wikipedia has a cool rotating circumpolar graph and a good explanation of circumpolar stars.

Keep looking up.

Photo credit: NASA Planetary Photo Journal Collection. IRAC Image: NASA/JPL-Caltech/Harvard-Smithsonian CfA/ESA/STScI Visible Light Image: NASA/JPL-Caltech/Harvard-Smithsonian CfA/DSS

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