Heavenly Skies: Guidance for seeking the small bear, Ursa MinorBy: Gene Grahek, Special to Gold Country News Service
Ursa Minor is Latin for “smaller” or “little bear” and is one of the five circumpolar constellations in the northern sky.
It is a smaller companion to the larger Ursa Major constellation. Their relatively close proximity is not the only trait they share in common as they both represent bears and contain prominent asterisms. In ancient times they were actually thought to be dogs.
This would account for the multiple handle stars being thought of as tails. Since real bears have short tails, something would have to be done to explain the discrepancy. The ancients decided the tails were stretched when the legendary god Zeus threw the bears into the sky by their tails and this is how we know them today. Just as Ursa Major has the well-known asterism called the Big Dipper, Ursa Minor has the Little Dipper.
Although both asterisms contain the same seven star groupings that represent the handle and bowl, the Little Dipper’s handle curves in the opposite direction. The dimness of the Little Dipper’s stars makes it hard to see in less than ideal viewing conditions.
Ursa Minor consists of seven visible stars that make up the Little Dipper. Although having few deep sky objects, it does have one barred spiral galaxy called NGC 6217 at a mere 60 million light-years away. The barred description refers to a bar appearance across the galaxies center caused by the light of millions of stars. It also contains a little-known meteor shower called the Ursids which peak around Dec. 22 each year.
The unique distinction of Ursa Minor is that it contains Polaris, the first star of the little bear’s tail and the present-day North Star. Being the brightest star in the constellation, it has a variable magnitude of about 2.0. This supergiant star has a diameter 30 times our sun.
Since our earth rotates on its axis, an imaginary line drawn through the axis and extended north beyond Earth into space would point to a particular area in the sky. This point is called the north celestial pole and is the point in the sky about which all stars seen from the Northern Hemisphere rotate. Any star near this we refer to as the North Pole Star or North Star. Polaris is the current North Star now but it has not always been nor will it continue to be in the future. Our sun and moon’s gravitational forces cause a motion or wobbling in the Earth’s rotation known as precession. Think of a spinning top that starts to spin slower and begins to wobble. This wobble causes the extended axis line of the top to make an imaginary circle in the sky thereby changing the location of the North Star. Precession takes around 27,000 years to complete its cycle.
Approximately 5,000 years ago the star Thuban in Draco was the pole star and was used for orientation when the pyramids were being built. The star Vega located in Lyra is the second brightest star in the northern hemisphere and was the pole star about 12,000 years ago. If you can wait long enough, Vega will again become the pole star in the year 13,727.
How do we find the Little Dipper? Locate and follow the three stars of the handle of the Big Dipper to the bowl or saucepan. Then find the two stars opposite the handle that make up the bowl’s outer edge. Draw a line from the outer edge of the bowl’s fainter star up through the brighter star. Continue following this line about five times the distance between the two stars. You are now at the North Star known as Polaris which represents the first star of the little bear’s tail. Now comes the hard part of seeking the rest of the dipper’s outline.
Come visit us at the Cameron Park Rotary Club Community Observatory located in Placerville to view the wonders of the night sky. For operating hours, directions and more information see www.communityobservatory.com and don’t forget to like us on Facebook.
Gene Grahek is a Lead Docent for the Cameron Park Rotary Club Community Observatory.