Polaris(redirected from Alpha Ursae Minoris)
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Polaris(poh-lar -is, -la -ris) (North Star; α UMi) A remote creamy-yellow supergiant that is the brightest star in the constellation Ursa Minor. It lies very close to the north celestial pole (dec: 89°16′) and is the present pole star. Its position is found by means of the Pointers in the Plough. Polaris is a classical Cepheid variable (period 3.97 days) but its pulsations have decreased rapidly since about the mid-1970s. It forms an optical double with a 9th-magnitude F3 V companion. mv : 2.0; Mv : -2.9; spectral type: F8 Ib; distance: 97 pc.
(Alpha Ursae Minoris, the North Star), a bright star of the second magnitude near the north celestial pole and thus useful for determining the bearing of the sun and a particular area’s geographic latitude, which is approximately equal to the altitude of Polaris above the horizon. In 1975, Polaris was 51′ in angular distance from the celestial pole. As consequence of precession, this distance decreases almost 17″ per year and will attain its minimum (28′) around the year 2100. Polaris can be found in the sky by the method indicated in Figure 1. The precise azimuth and latitude of a location can be determined from Polaris using ephemerides published in astronomical annuals.
Polaris is a triple star. Its bright component is a cepheid (variable star) with a brightness-variation amplitude of 0.14 stellar magnitude and a period of about four days.