Circumpolar Stars in the Night Sky

sky_circumpolar stars
Circumpolar stars in the nigh sky.

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

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 at the 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.

What is a Circumpolar Star?

Circumpolar is Latin for “around the pole”. Circumpolar stars are any stars that appear to circle around the Earth’s north or south poles.

Circumpolar stars always appear in the night sky. Circumpolar stars never rise or set and are always above the horizon. These stars appear high in the night sky. They are visible for the entire night, all year around.

At the Earth’s North and South poles, all stars appear as circumpolar. If we are not at the north or south poles only certain stars, are always in the night sky, all year around.

North Star and South Star?

At the top  and the bottom of this spinning sphere we call Earth, are the poles. Each “pole” or hemisphere has its own set of constellations.

In Earth’s northern hemisphere, we have a star that is close to the point in the sky we call, true north. This star is named Polaris. We call it the north star.

Polaris is a bright star, always visible in the night sky. It stays in a near constant spot. It’s bright visibility makes it good to use for navigation purposes.

The southern hemisphere, doesn’t have a star that is located at true south. The closest star, is named Sigma Octantis. It is called the south pole star. Sigma Octantis is a dimly lit star that is barely visible on a clear night. Being so dimly lit it is not suitable to use for navigation purposes.

Circumpolar stars seem to rotate around Earth’s poles and the polar stars.  Northern hemisphere stars seem to rotate around the north star. Southern hemisphere stars rotate near a point close to Sigma Octantis.

At Earth’s poles all stars in the hemisphere appear circumpolar. At the notth pole, all the stars in the northern nemisphere appear as circumpolar. Meaning the stars are always in the night sky, all year around.

How to Find Polaris 

Stars Move from East to West

When we look north, it appears objects in the sky are moving from east to west. This is true for both the northern and southern hemisphereWe see the Sun as rising in the east and setting in the west. The Sun, Moon, stars and planets move from east to west in the sky, just like the Sun.

Equatorial Stars are Not Circumpolar Stars

For you to see a star constellation, it has to be in your hemisphere.

I live in the northern hemisphere. I can’t see stars high in the southern hemisphere sky. The high southern hemisphere sky is too far below the equator for me to see those stars. Those stars high in the southern hemisphere sky are circling the south pole. Those are the circumpolar stars of the southern hemisphere. They only way for me to see them is to go to Australia, New Zealand or other place in the southern hemisphere.

The stars you will never see in your horizon are called, ‘never rise stars’ for your hemisphere. The southern hemisphere stars I will never see in my northern hemisphere sky are called,’never-rise’ stars for the northern hemisphere.  My northern hemisphere circumpolar stars (and others) are ‘never rise’ stars for those down under in Earth’s southern hemisphere.

At the equator, no star is circumpolar. At the equator there aren’t any star constellations which are always in the sky.

As the Earth rotates some stars which are closer to the equator sink below the horizon. At the equator, some stars rise and set daily.

Seasonal Stars Rise and Set at the Horizon

If the star constellation is near the equator the rotation of the Earth will cause the constellation to be seen only at certain times of the year. These are called ‘rise and set stars’.

These stars appear in the sky at different times of the year.   I like to call them seasonal stars.

Seasonal stars are good for ‘marking the passage of time and the seasons of the year. When a seasonal star constellations appear in the night sky, you know the Earth’s rotation has reached a specific point in the year.

Circumpolar Stars in the Northern Hemisphere

The northern hemisphere 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, Pa., 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 “M”
  • Cepheus (the King)
  • Draco (the Dragon)
  • Camelopardalis

What stars you see in the night sky depends on your latitude. Or how far above the equator you are. If you are close to the north pole, you will see more. The farther away you are form the poles, you wil see fewer stars.

Here is a quick video explaining Circumpolar North

Circumpolar Stars in 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

The closer you are to the southern pole the more of these eleven constellations you will see.

Here is a video that explains The Sky in the Circumpolar South.

Learning to Find Cassiopeia

To learn these constellations pick out one that resonates with you. The first one I learned was Cassiopeia. It is knownin Greek mythology, the constellation is called, the ‘Lady in the Chair’ or ‘the Queen on her Throne’.

I choose Cassiopeia because my astrology birth sign is Virgo the Virgin. Another woman. And the ‘M’ shape is easy to pick out.

The video below is a kids’ video but gives a good overview of finding the Cassiopeia.

Finding your Circumpolar Stars

By knowing the circumpolar stars you will know the main constellations, that are always in your night sky. 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.

About Constellations (Lunar and Planetary Institute)

Indian Moon names

The Seasonal Nature Journal 

Let Me Know in the Comments Below

This posts has been greatly expnaded and updated since it was first published in 2011.

I hope you found this post useful. It you have a comment or question, please let me know in the comments below.

 

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