Polaris

All present and correct

To all intents and purposes

Let the cool goddess rust away

Close your eyes and think of England

Polaris is a star in the northern circumpolar constellation of Ursa Minor. It is designated Ursae Minoris and is commonly called the North Star or Pole Star. With an apparent magnitude that fluctuates around 1.98, it is the brightest star in the constellation and is readily visible to the Polaris is a star in the northern circumpolar constellation of Ursa Minor.

As the closest Cepheid variable its distance is used as part of the cosmic distance ladder. The revised Hipparcos stellar parallax gives a distance to Polaris of about 433 light-years, while the successor mission Gaia gives a distance of about 448 light-years. Calculations by other methods vary widely.

Although appearing to the naked eye as a single point of light, Polaris is a triple star system, composed of the primary, a yellow supergiant designated Polaris Aa, in orbit with a smaller companion, Polaris Ab; the pair is in a wider orbit with Polaris B. The outer pair AB were discovered in August 1779 by William Herschel, where the A refers to what is now known to be the Aa/Ab pair.

Because Polaris lies nearly in a direct line with the Earth’s rotational axis above the North Pole—the north celestial pole—Polaris stands almost motionless in the sky, and all the stars of the northern sky appear to rotate around it. Therefore, it makes an excellent fixed point from which to draw measurements for celestial navigation and for astrometry. The elevation of the star above the horizon gives the approximate latitude of the observer.

IN ANTIQUITY, POLARIS WAS NOT YET THE CLOSEST NAKED-EYE STAR TO THE CELESTIAL POLE, AND THE ENTIRE CONSTELLATION OF URSA MINOR WAS USED FOR NAVIGATION RATHER THAN ANY SINGLE STAR. 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.

Ursa Minor, also known as the Little Bear, is a constellation located in the far northern sky. As with the Great Bear, the tail of the Little Bear may also be seen as the handle of a ladle, hence the North American name, Little Dipper: seven stars with four in its bowl like its partner the Big Dipper. Ursa Minor was one of the 48 constellations listed by the 2nd-century astronomer Ptolemy, and remains one of the 88 modern constellations. Ursa Minor has traditionally been important for navigation, particularly by mariners, because of Polaris being the north pole star. Polaris, the brightest star in the constellation, is a yellow-white supergiant and the brightest Cepheid variable star in the night sky, ranging in apparent magnitude from 1.97 to 2.00. Beta Ursae Minoris, also known as Kochab, is an aging star that has swollen and cooled to become an orange giant with an apparent magnitude of 2.08, only slightly fainter than Polaris. Kochab and 3rd-magnitude Gamma Ursae Minoris have been called the guardians of the pole star or Guardians of The Pole. Planets have been detected orbiting four of the stars, including Kochab. The constellation also contains an isolated neutron star—Calvera—and H1504+65, the hottest white dwarf yet discovered, with a surface temperature of 200,000 K. Ursa Minor is bordered by Camelopardalis to the west, Draco to the west, and Cepheus to the east. Covering 256 square degrees, it ranks 56th of the 88 constellations in size. Ursa Minor is colloquially known in the US as the Little Dipper because its seven brightest stars seem to form the shape of a dipper (ladle or scoop). The star at the end of the dipper handle is Polaris. Polaris can also be found by following a line through the two stars—Alpha and Beta Ursae Majoris, popularly called the Pointers—that form the end of the bowl of the Big Dipper, for 30 degrees (three upright fists at arms’ length) across the night sky. The four stars constituting the bowl of the Little Dipper are of second, third, fourth, and fifth magnitudes, respectively, and provide an easy guide to determining what magnitude stars are visible, useful for city dwellers or testing one’s eyesight.