Polaris is a star in the northern circumpolar constellation of Ursa Minor.
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13 Facts About Polaris
2.
Polaris Aa is an evolved yellow supergiant of spectral type F7Ib with 5.
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3.
Since Polaris A is a known cepheid variable, J H Moore in 1927 demonstrated that the changes in velocity along the line of sight were due to a combination of the four-day pulsation period combined with a much longer orbital period and a large eccentricity of around 0.
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4.
Polaris Aa, the supergiant primary component, is a low-amplitude Population I classical Cepheid variable, although it was once thought to be a type II Cepheid due to its high galactic latitude.
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5.
The variability of Polaris had been suspected since 1852; this variation was confirmed by Ejnar Hertzsprung in 1911.
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6.
Authors disagree on whether Polaris is a fundamental or first-overtone pulsator and on whether it is crossing the instability strip for the first time or not.
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7.
Twice in each sidereal day Polaris' azimuth is true north; the rest of the time it is displaced eastward or westward, and the bearing must be corrected using tables or a rule of thumb.
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8.
However, as one of the brighter stars close to the celestial pole, Polaris was used for navigation at least from late antiquity, and described as ae? fa??? "always visible" by Stobaeus, and it could reasonably be described as stella polaris from about the High Middle Ages.
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9.
Polaris was referenced in Nathaniel Bowditch's 1802 book, American Practical Navigator, where it is listed as one of the navigational stars.
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10.
Polaris moved close enough to the pole to be the closest naked-eye star, even though still at a distance of several degrees, in the early medieval period, and numerous names referring to this characteristic as polar star have been in use since the medieval period.
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11.
Polaris is the closest Cepheid variable to Earth so its physical parameters are of critical importance to the whole astronomical distance scale.
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12.
The Hipparcos reduction specifically for Polaris has been re-examined and reaffirmed but there is still not widespread agreement about the distance.
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13.
Polaris is the brightest star in the constellation of Ursa Minor.
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