Spring stargazers should watch for 'bears'

On March 21, the sun climbs north across the celestial equator (actually, Earth dips south on its axis exposing the northern latitudes to more direct rays from the sun). It is the first day of spring!

We stargazers, like crocuses pushing up through soil, leaves, and even snow, can now come out a little later, and look a little longer, at the heavenly wonders.

There are three objects to study in early spring - the Big Dipper in the constellation Ursa Major (great bear), the Little Dipper in the constellation Ursa Minor (little bear), and Polaris, the North Star at the tip of Ursa Minor's tail.

The Big Dipper is the most recognized configuration in the northern skies, but it's not a constellation. Officially, there are 88 groups of stars listed as constellations. The dipper has no official status other than as a striking part of the constellation Ursa Major. Such a star pattern is called an asterism. Also, remember, the stars we see making up a constellation are not necessarily close to each other in space. The distances are so great, we see them as if flattened on a black pane of glass.

Polaris is the one star that does not seem to move as Earth turns. Because its place in the sky does not depend on the time of day or day of the year, it has long been of great importance to sailors. With a visible magnitude of minus 1.96 it isn't the brightest star in the sky. But it's the brightest star in its part of the sky. For anyone at latitude 41 degrees north (New York city) or above, Polaris never goes below the horizon.

The Big Dipper serves as an astronomical signpost to Polaris. Merak (ME-rak) and Dubhe (DU-bee), the stars at the front of the cup, are called the "pointers." No matter how the asterism spins in the sky, follow these two stars out of the cup in a straight line and they will point to Polaris. If you're lost at night, look up at Polaris and stretch your arms out. Your right arm will point east, your left, west, with south at your back.

Just fixing our gaze on Polaris offers a deep sense of the rhythms of the heavens. Imagine Polaris as the center of a wheel, with the Big and Little Dippers rotating about it. Sensory evidence to the contrary, it is you who are turning, not the stars. The astronomical fact, contradicting the sensory evidence, is a telling example of how planet Earth and its inhabitants are part of one big heavenly dance.

Scientifically, we know that Polaris is half a degree away from true north, or the celestial pole (a line drawn through the center of Earth from north to south). Astronomers calculate that the alignment of Polaris with Earth's axis is improving. Alignment will be closest in 2102. No chance of losing your way on a clear night.

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