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North Star Definition

If you think of the night sky as a tent with a center tent pole, the North Star, Polaris, is the place where this pole fits at the top of the tent. The tent pole is an extension of the earth's axis going up to the sky from the North Pole. While the constellations seem to rotate around the night sky, the North Star seems to stay in its fixed position.

Identification
- The North Star is the brightest star in the constellation Ursa Minor, which we call the Little Dipper. To find it, locate the Big Dipper, otherwise known as Ursa Major. This looks like a trapezoid with a handle. The two stars at the outer side of the trapezoid, the dipper, are called the "pointer stars." They point, along a 30 degree angle, toward the North Star.
Location
- If you stand on earth at a point that is on the 40 degrees north line of latitude, at 9 in the evening, Polaris will be directly overhead. In fact, if you extend the North Pole into the sky, where it hits is the North Star. This is the star that is most nearly 90 degrees from every point on the celestial equator.
Time Frame
- While Polaris is the North Star now, this is not always the case. The place where the earth's polar axis pierced the sky changes because of precession, which means that the equinoxes seem to move because of the shape of the earth at the equator. Vega will become the North Star in about 12,000 years. Alpha Draconis was the North Star 3,000 years ago.
Features
- Polaris, the current North Star, is brighter than our sun. It is 50 light years away from the earth. This means that the light we can see when we look at the North Star today left that star 50 years ago. Because it is a Cepheid variable, the brightness, or magnetude, of Polaris changes every four days.
Potential
- Because the North Star does not change its position relative to the earth, you can use the pointer stars of the Big Dipper or the star Caph in Cassiopeia as a clock at night in the Northern Hemisphere. First imagine a clock face where the North Star is at the center. The pointer stars are like the tip of the hour hand. Find the "Local Star Time" by subtracting the number where the pointers point from twelve. Multiply that number by two and add 11. Once you have the Local Star Time, change it to your "Local Sun Time." Start with March 23. Subtract two hours for every full month that has elapsed between that date and the current date. Then subtract four minutes times each day that is left over. Take this number and subtract it from the Local Star Time. This gives you the current time. Of course, you will have to make an additional adjustment if your area is on Daylight Saving Time.

Astronomy