The definition of Ursa Minor
Ursa Minor is a constellation closest to the north celestial pole,which is included in Ptolemy and the modern 88 constellations. Ursa Minor marks the north celestial pole, and the brightest star in this constellation:α UMi, is the Polaris.
The tail of the Ursa Minor can be seen as the handle of a bucket (or spoon), hence it also can be called “Little Dipper” : four of the seven stars form a ladle on the dipper, like the Big Dipper. Ptolemy (the astronomer in the 2nd century AD) included Ursa Minor in his 48 constellations.
The main information of Ursa Minor
| Right Ascension | 15h |
| Declination | 70 |
| Area | 256km2 |
| Area of ranking | 56 |
| Number of bright star | 2 |
| Brightest star | α UMi |
| Meteor shower | Ursids |
| Adjoining constellation | Draco, Camelopardalis, Cephei |
| Optimal observational duration | June |
| Optimal observational latitude | mid and high latitudes in the northern hemisphere all year round |
| Apparent magnitude of brightest star | 2.02 |
| Fully visible region | 90°N-0°S |
Traditionally Ursa Minor has been an important navigation constellation, especially in voyage, because its main symbol is the Polaris.
The characteristics of Ursa Minor
Observation characteristics
If we link the seven bright stars in Ursa Minor together, they will form a dipper similar to the Big Dipper in the Ursa Minor, so they are also called the Little Dipper. At the beginning of the handle is α UMi, which is now the Polaris, indicating the north celestial pole. Polaris can be found by leading a straight line outward from the mouth of Ursa Major through two stars, β UMa and α UMa, and extending to five times the distance between the two stars.
Shape features
The main bright stars in the star map are linked together to form a little dipper rather than a bear. This dipper of Ursa Minor is much smaller than that of the Big Dipper, and not nearly as dramatic as the Big Dipper.
The stars in Ursa Minor
Α UMi is the brightest star in Ursa Minor. It is a yellow-white supergiant and also the brightest cepheid variable star in the night sky, with an apparent magnitude range of 1.97 to 2.00. However, β UMi is late in its life, having expanded and cooled into an orange giant with an apparent magnitude of 2.08, just a little dimmer than α UMi. Β UMi and γ UMi were once known as the guardians of Polaris. Planets have been detected around four stars in the Ursa Minor, including β UMi. Ursa Minor also contains an isolated neutron star, Cavila, and the hottest known White Dwarf, H1504+65, with a surface temperature of 200,000 kelvin.
α UMi
It is one of the major bright stars in the northern sky, located at right ascension 2h31m48.71s, declination 89°5’50.6″. Because it is the closest star to the north celestial pole, it is known as the Polaris. Polaris is also a variable star, with an apparent magnitude of 1.95 to 2.04 (ranking 48th in brightness throughout the whole sky). It is also a triad (a three-star system) about 400 light-years away.
From the mouth of Big Dipper, α UMa and β UMa, to lead a straight line to the north, extended to five times their distance from the other side, there is a bright star, the famous Polaris.
In addition, we can also find Polaris from the Cassiopeia: first find the midpoint of Cassiopeia ε and γ, and then connect the Cassiopeia δ and this midpoint. Finally, you can find it by extending the line to the north.
Stargazers often photograph concentric circles with Polaris as the center of the star’s orbit.
β UMi
It is the second of the five stars in the North Pole, one of the major bright stars in the northern sky, located at right ascension 14 h50m42.37s , declination 74°9’19.7″. Its visual magnitude is 2.2. β UMi and γ are located in the mouth of Little Dipper, so they are collectively known as the “polar protector”.
γ UMi
It is the first of the five stars in the North Pole, one of the major bright stars in the northern sky, located at right ascension 15h20m43.73s, declination 71°50’2.5″. Its visual magnitude is 2.2.
Ursids
Ursids didn’t make much of attention during the first half of the 80s. However, on December 22, 1986, several observers in Europe reported something surprising. Belgium’s Luc Gobin reported very high signal at 66.17MHz. According to his monitoring, the signal on the 23rd was three times higher than the previous days. George Spalding of Britain confirmed the Belgian’s result visually, by observing an explosion of ZHR 87+-29 on the 22nd.
Kai Gaarder in Norway also observed a violent activity with an ZHR of 64+-11 on the night of The 22nd, with an average magnitude of 1.9. A total of 94 meteors appeared within four hours. His compatriot Lars Trygve Heen saw 75 meteors in two hours, with an ZHR of 122+-17 and an average magnitude of 2.61. They saw only four or two meteors each the next day. In the 175 observed meteors, 17.1% left trails, 66 brighter than magnitude 2, 51.5% are white, 33.3% are yellow, 7.6% are red, 2.3% are green, and 5.3% are blue.
Ursids is a poorly observed northern hemisphere meteor shower, but has produced at least two major eruptions in the past 60 years, in 1945 and 1986 respectively. Other increases, as recently in 1988,1994 and 2000, have also been reported. Another similar phenomena may have been easily missed, either by bad weather or by too few observers. All observation methods can be used for this meteor shower because many of its meteors are dark, and there is so little work available on this meteor cluster that it is impossible to draw precise conclusions.
The Mythology of Ursa Minor
One of the mythology says that Ursa Minor represents one of the goddesses who raised Zeus. But the more accepted one is related to Ursa Major.
Ursa Minor stands for Arcas, son of Zeus. Once Zeus fell in love with a servant named Callisto (a servant of Artemis), and soon Callisto became pregnant and gave birth to Arcas.
After knowing this, Hera (the queen) was angry and changed Calisto into a bear and forced her to live in the forest. After many years, Calisto’s son Arcas grew up and became an excellent hunter. That day Arcas was hunting in the forest. Calisto recognized her son and forgot that she was a bear, so she ran toward him. But Arcas did not know that this horrible bear was his mother, so he raised his spear at this bear. In this danger, Zeus hurried to change Arcas into a bear too. Arcas, who turned into a bear, recognized his mother and avoided the tragedy of family killing. Later, Zeus took the two bears to the sky together and gave them two places of honor among the stars. They were Ursa Major and Ursa Minor.
Then, Hera sent a hunter with two ferocious hounds to follow the bears closely. The hunter is the Bootes in the sky, and the two hounds he is leading are the Canes Venatici.
When the Ancient Greeks saw the great bear wandering in the sky night after night and never falling below the horizon, they thought it must be one of Hera’s tricks. Hera sent hunters and hounds to chase the bear mother and son, but still not give up, she went to the sea, to ask her brother Poseidon for help. He believed his sister’s story and granted her request. Therefore, we can see that all the other constellations rise in the east and set in the west, and always sink below the horizon for a period of time to rest in the realm of Neptune, except the tow bears. It was just as well, for Calisto, she could always stay by her son, in case Hera came up with any bad ideas.
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