Polaris and the Constellation Ursa minor
Modern astrology recognises 88 constellations in total and these help to define portions of the night sky as a whole as viewed from Earth. Many books on the subject present what look a lot like maps of the night sky with dotted lines separating one constellation from its neighbour like a state line in an atlas.
The object of this and the following blogs on the subject is to help you identify, remember and fix in your head a working map of the night sky as seen from the Northern hemisphere. Just like the star maps presented in field guides you will be able to build up a working knowledge of how one constellation relates to its neighbour.
As your familiarity with the night sky grows so to your ability to ascertain direction will improve. We will start with a star and a constellation that has been enormously important as a navigational aid for many centuries and will continue to be for many more – Polaris and its constellation Ursa minor. This is your stepping stone to understanding the night sky.
Just as Polaris can help you find North it will also give you a fixed point of reference to work from helping you jump to and identify other constellations. If you get lost, go back to Polaris and start again!
The North Star and the constellation Ursa minor
Ursa minor translates from Latin to Lesser bear which is supposed to relate to the constellation looking like this animal. Like many of our constellations however it has little resemblance to a bear and more accurately reflects its other commonly used name – the little dipper.
As you can see from the diagram the brightest stars of Ursa minor represent a pan or drinking vessel shape much like the bright stars in its neighbouring and much larger constellation of Ursa major – Greater bear. This constellation will be covered in detail in the following blog.
The patterns of bright stars we recognise as Ursa minor or Ursa major are just part of the picture. The true constellation of Ursa minor has many more stars associated with it than the 7 bright ones you can often see at night. All of these associated stars together form the constellation Ursa minor while the 7 brightest stars we recognise form something called an asterism. This is just a fancy word for a pattern of stars.
So to clarify the 7 bright stars in the asterism which looks like the above diagram are just part of the true constellation Ursa minor. This is true of many other constellations for example the large obvious pan shape in Ursa major, the three bright stars forming the belt in the constellation Orion, the sideways triangle of the eyes and horns in the constellation Taurus – these are all asterisms within constellations containing many more stars.
I have started with the constellation Ursa minor purely and simply because it contains the North Star or Alpha ursae minoris to give it its scientific name. After the Sun this is the single most important heavenly body to any navigator be them sailor, traveller or bush crafter.
Its importance as a navigational aid lies in the fact that it appears to remain motionless, fixed above the North celestial pole while all the other constellations circle anti clockwise around it. The more familiar you become with the night sky immediately around the North Star the quicker you will be able to identify it and use it to determine direction.
More than this you can begin to build a map of the sky. Starting with the North Star we can begin to add constellations one at a time moving away from Ursa minor in different directions. If you get confused or lost all you do is go back to the North Star and start again. With practice it is possible to fill in the entire night sky with constellations working your way outwards from ursa minor and the North Star.
If you were to film the night sky looking directly at the North Star using time lapse photography you would see every star in the heavens scribe a perfect circle around it. This movement high lights why the next two brightest stars in Ursa minor are commonly named the ‘guard stars’ or ‘sentinels’ – because they are the closest, brightest stars to the North Star and appear to march around and around it on sentry duty.
In ancient history Ursa minor was considered a part of the much larger neighbouring constellation of Draco –The Dragon, we will come back to him in later blogs. This makes sense as bears would have been virtually unknown to the Egyptian culture during this time. Ursa minor was instead seen as the wing of the dragon and you can still see why when you look at it today. Many sources on the origins of constellations quote that Ursa minor, as the lesser bear, came into existence around the 6th Century BC but it was certainly known and widely used by navigators before that date back to a very early time indeed.
Interestingly one of the previously explained ‘guard stars’ named Kochab was thought by the ancient Egyptians to be linked to reincarnation and immortality and there is a slot in the roof of the Queen’s chamber inside the Great Pyramid angled directly at this star! Some writers argue that like many of the constellations close to Polaris in the Northern hemisphere Ursa minor never sets and so the association with eternal life may have come from this ancient observation.
Many ancient cultures including the Egyptians Arabians and Chinese saw the square pattern of stars in Ursa minor as the hole through which the Earths’ rotational bearing (axel) was located – pretty astute and although there is no physical bearing (is there…?) the net effect on how the stars appear to move is the same.
Imagine a pencil stuck through an orange, tilt the pencil slightly and rotate the top and bottom of the pencil in the same direction – the pencil would be the bearing around which the orange rotates exactly as the ancients understood the earth to rotate. Using the same analogy, Polaris would be located right on the sharp tip of the pencil lead and is the only fixed point when viewed by someone tiny standing on the surface of the orange…
Just to throw a spanner into the works, Polaris has not always been the pole star.
This is because the Earth is actually wobbling slightly on its axis. This wobble takes a very long time to become apparent but the effect over the ages has been that the Pole star (the star closest to the north rotational axis of the planet) has been a number of different stars in a number of different constellations!
Don’t panic though you only need to know the present day Polaris inside Ursa minor. You could teach this to your grandchildren who could teach it to theirs and so on for hundreds of years and Polaris will still appear where it does today. Eventually however the wobble effect will offset Polaris from the North rotational axis and in an estimated 5000 years from now the star of Alderamin in Cepheus will appear to be the motionless star in the Northern sky.
Looking at this phenomenon in reverse we know from the recordings of the ancient Egyptians (~3000 years ago) that they taught their children to use Thuban in Draco as their Polaris and navigational aid. Do not get Thuban confused with Eltanin which is Draco’s brightest star.
So for now we know that Polaris is a hugely important navigational aid as it appears to remain motionless. It is found inside the asterism of the lesser bear (or little dipper) which is part of the constellation Ursa minor.
Likely you already know this constellation well but if you don’t then spend a few nights locating it by using the far more obvious constellation of Ursa major (we will cover this fantastic constellation in the following blog).
If you are familiar with Ursa major (or the plough as you may know it) but not with Ursa minor then draw an imaginary line through the two end stars of the pan in Ursa major and extend this imaginary line upwards 5 x the distance between these two stars ( A and B in diagram) to find the first bright star you come to. You have just found Polaris inside Ursa minor.
Woodland Ways: Bushcraft UK