As long as humans have stared at the sky, our innate need to find patterns has led us to connect the dots between the stars, painting images from mythology and everyday life. Many of the patterns became accepted reference points in the sky, some with names dating back more than three millennia. Of the 88 constellations recognized by the International Astronomical Union, many rise and set as the Earth rotates through space, but others are visible all the time, or are circumpolar.
Why Are Some Constellations Circumpolar?
The planet rotates around its axis while orbiting the sun. The motion of the planet means that different regions of the sky rotate into and out of view from a human perspective. Earth's axis is more-or-less perpendicular to its orbit, so the view from the poles changes very little compared to the equator. Standing at the equator, the polar constellations are over your horizon, so all of the constellations you can see rotate in and out of view seasonally. You may notice that none of the circumpolar constellations are associated with zodiac signs, since zodiac constellations are nearer to the celestial equator, referenced to the sun since the planet tilts slightly on its axis, than the poles. As you move closer to the poles, you can see more and more circumpolar constellations.
Northern Hemisphere Circumpolar Constellations
Five primary circumpolar constellations are located between 40 and 50 degrees latitude in the Northern Hemisphere. Ursa Major, the big bear, is easily found in the sky because the back half of the bear is also known as the Big Dipper, technically an asterism and not a true constellation. Ursa Minor, the little bear, contains the most important star in the northern sky for navigation, Polaris, the North Star. Next to these two is Cassiopeia on her chair and her husband, Cepheus. The final circumpolar constellation is Draco, the dragon, just above Ursa Major. Moving up into the Arctic, Auriga, Camelopardis, Lynx and Perseus become circumpolar.
Southern Hemisphere Circumpolar Constellations
There are more constellations visible from the Southern Hemisphere because the South Pole faces the center of the galaxy and, consequently, more stars. There are three circumpolar constellations that are visible from most of the Southern Hemisphere. There is no bright pole star, but the primary navigational touchstone is Crux, or the Southern Cross. Next is Carina, or the keel, which was once part of a starry ship constellation. Centaurus, the centaur, rounds out the trio that is visible throughout the hemisphere. As you move toward the South Pole, Grus, Phoenix, Indus, Tucana, Pavo, Ara, Eridanus, Hydrus, Horologium, Reticulum, Octans, Apus, Triangulum Australe, Lupus, Circinus, Musca, Vela, Puppis, Dorado and Chamaeleon become visible year-round.
How to Locate Constellations
You can locate constellations with the use of a star chart, or map of the sky. These charts are usually referenced to your latitude and the season. In the Northern Hemisphere, look north and locate Polaris, the North Star. Using the Polaris as a reference point, you can work your way across the sky, identifying constellations. In the Southern Hemisphere, look to the south and use Crux as a reference point.
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