α Ursae Minoris
(and other stars of Ursa Minor)

Alpha Ursae Minoris is much better known as The Pole Star, or Polaris, or simply as The North Pole although this isn't quite accurate.

The Celestial North Pole is 45 arcminutes from Polaris, a distance so minute that for all practical purposes Polaris does mark the northern point on the celestial sphere around which all other stars revolve.

Knowing where the celestial north pole is (and we'll make that concession -- whenever we mention 'the celestial north pole' or CNP we really mean Polaris) is very useful as other stars can be more easily found once the pole is spotted. For example, moving north from any other star means drawing an imaginary line from that star to Polaris, so this is obviously a key star to locate.

Most people learn to find the north pole by starting at the Big Dipper (Plough: UK) and using the 'pointer stars' (alpha UMa and beta UMa) which take the observer right to Polaris.

This is the view of Polaris on an Autumn evening, looking north (the Big Dipper is just below, out of view and right-side up, between the horizon and the Pole Star): binoculars.

Alpha UMi is a multiple star system (Struve 93):
     AB: 2.1, 9.1; 233º, 18.1".
     AC: 2.1, 13.8; 98º, 38.7".

Apart from Polaris, the most useful star is beta (2.0), known as ‘Kochab’, which is Hebraic rather than Arabian, meaning the North Star.
     The reason beta is called the North Star may be due to the fact that three thousand years ago beta Ursae Minoris was closer to the celestial north pole than was Polaris.
     Kochab is not only the brightest bowl star, but it shines with a very noticeable orange-metallic colour, making it easy to spot. Beta is a giant, with a radius 42 times that of the Sun.
     The quickest way to find Kochab is to first locate Cassiopeia, then move in the opposite direction from the pole star about the same distance to the bright orange star. This will be Kochab, beta UMi.

Gamma is Pherkad. Together with Kochab these two are the ‘Guardians of the Pole’ as they endlessly circle the pole.

The stars of Ursa Minor have different brightnesses, roughly a magnitude difference, which will allow you to judge just how good the skies are:

  1. alpha: 2.0
  2. gamma: 3.0
  3. epsilon: 4.2
  4. eta: 5.0
  5. lambda: 6.3

On any night then a quick check of how well you can see these various stars will indicate how successful that evening's observation should be.

If you move one binocular field northwest of beta, practically due south of Polaris, you'll encounter the fairly bright 5 UMi.

Near the western edge of your glasses are a trio of dimmer stars; the upper star here is h2682, a delightful celestial triangle with a yellow-white primary and two blueish companions:
      AB: 6.7, 10.3; 282º, 25.8".
      AC: 6.7, 9.2; 317º, 43.8".

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