Ursa Minor: The Lesser Bear

Colton Clement

PHYS-1040, Stephen Preston

Constellation Paper

April 11th, 2019

The Constellation of Ursa Minor

The constellation Ursa Minor contains a famous small grouping of distinctive stars called an asterism, known to most as the Little Dipper. Another famous asterism, the Big Dipper, found in the constellation Ursa Major, translates to great bear and mirrors Ursa Minor in both name and appearance, both having the appearance ladles or pots, one being much larger than the other. Ursa Major consists of much more luminous stars that Ursa Minor and is easier to spot in the sky. Ursa Major can be used to help located Ursa Minor, which can appear as more of a small ladle, while Ursa Major has more of a “pan-like” appearance being larger and brighter. Both constellations have relations to Polaris a famous star in the northern region of our sky, known to many as the “North Star”. Even though Polaris exists in Ursa Minor. (Dolan, EarthSky)

Ursa Minor is the 56th largest constellation by size consisting of an area of 256 square degrees. Ursa Minor is located in the 3rd quadrant of the Northern Hemisphere (NQ3) and is seen at latitudes between +60 degrees and -10 degrees. It is neighbored by constellations, Camelopardalis, Draco, and Cepheus. Ursa Minor only has one star with a confirmed planet, however there is evidence of a few others that haven’t been confirmed. (Constellation Guide)

Primary Stars in Ursa Minor

Polaris has great importance to many as having a relationship with Earth's axis. The Earth’s axis points almost directly towards Polaris. This is significant in that if you were in the Northern Hemisphere, locating Polaris in the night sky and following it would lead a person north towards our northern pole, until it were directly above you. Polaris is located 434 light years away from us an has a luminosity of nearly 4,000 times that of our sun. Even with that, Polaris only has a magnitude of brightness of 2, and while there is a common misconception that Polaris is “the brightest star in the sky”, other objects in our sky are much brighter, with magnitudes of 1 and even 0. Polaris stands out as the end of the handle of the Little Dipper in Ursa Minor and can be found by following the pointer stars Dubhe and Merak, located in the nearby Big Dipper in Ursa Major and following them about 5 times the angle. Earth currently is in precision, meaning that our axis, over thousands of years, is slowly rotating like a top. As time passes Polaris won’t actually be our north star anymore, as our axis will have shifted away from Polaris and towards Vega, a star in the constellation Lyra, then back to Polaris again. In 2600 BC the star Thuban, in the constellation Draco, was the North Star and in 400 BC Kochab was the north star. We are still in the cycle in which Polaris closes in closer to our northern pole and on March 24, 2100 it will be as close to the pole as it will ever be at 27.15 arcseconds, slightly less than the moon's diameter, before beginning to move away from from the pole. There are two other stars of importance in the “bowl” of the Little Dipper with records of higher luminosity unlike the rest of the mostly dim constellation. The “Guardians of the Pole” were mentioned in logs by Christopher Columbus and other navigators used them as utility in measuring the hour of night as well as their position in the seas. The guardians are Kochab a second magnitude star with an orange hue and the more dim Pherkab being a third magnitude star. (Rao)

Mythology of Ursa Minor

Ursa Major and Ursa Minor are connected when discussing their origins in mythology. Artemis, the Greek Goddess of the Moon, had a group of beautiful nymphs, sworn by a vow to chastity. One of these nymphs, Callisto, most commonly referred to as the most “lovely”, had caught the attention of Zeus, the god of gods, who had a particular fondness for mortal women. Zeus disguised himself as Apollo, the god of music and Artemis’ brother, and pursued Callisto, eventually becoming lovers. They bore a child of the name Arcas (from the Greek word for “bear”). Knowing that Artemis would be upset for breaking the vow of chastity and more so for the protection of his lover, Zeus changed Callisto into a bear. Callisto still possessed human emotions, which made it difficult for her to befriend other animals and any human that she would interact with would be hunters looking to hunt or kill her. Many years later, her son, Arcas, was hunting in the forest when he saw a large bear who was in fact, his mother. As Arcas goes for the killing blow, Zeus intervened and transformed Arcas into a small bear so he was able to immediately recognize his mother. Callisto and Arcs, no longer lonely and together again, were transported to the heavens. Callisto becoming the larger Ursa Major and Arcas becoming the smaller Ursa Minor. (Mythology of the constellation Ursa Minor)

Chinese mythology didn’t recognize the Little Dipper that we do, but they did have a similar dipper shape called Gouchen (meaning “curved array”) that was formed with many of the stars in our big dipper, plus two unlabeled stars in a Cepheus, a separate constellation. Polaris was in Gouchen, but it was known as Tianhuang Dadi, meaning “great emperor of heaven” referencing their highest god. In their book The Chinese Sky During the Han (1997)(Xiachun, Kistemaker) Sun Xiaochun and Jacob Kistemaker suggest that this name wasn’t applied to Polaris, but actually to a fainter star next to it, or a blank area nearby, suggesting that the Chinese believed that their almighty deity would be invisible and deceiving. (Ridpath)

Notable Objects in Ursa Minor

Other than the asterism known as the Little Dipper, Ursa Minor is on the devoid side of deep-sky objects. The Ursa Minor Dwarf is a spheroidal dwarf galaxy discovered during the Palomar Sky Survey in 1955 and is a satellite galaxy of the Milky Way consisting of mainly older stars with little to no ongoing star formation and thought to be as old as the Milky Way itself. (Bergh) Another notable galaxy with a very different history of star formation is NGC 6217, a barred spiral galaxy located 67 million light years away. Because of it’s high rate of star formation compared to a typical galaxy, it has been since characterized a starburst galaxy. (Royal Astronomy Society)

NGC 6217 is a third galaxy in Ursa Minor and is classified as an active supergiant elliptical radio galaxy that is known for being very visible in the radio wavelength. This galaxy is more than 340 million light-years away from Earth and is one of the most extreme examples of a Seyfert Galaxy, having a quasar-like nuclei being very bright with electromagnetic radiation and high ionization emission lines. NGC 6217 is also known for having a jet of radio waves, one of the brightest ever detected, detected in 1977. (SIMBAD Astronomical Database)

Ursa Minor is home to a prominent meteor shower called the Ursids, and can be seen annually around December 17th and runs for over a week, until the 25th or 26th of December. This shower has a radiant point that it is named after near the star Kochab. The Ursids have a primarily narrow stream, one observationalist, Norman W. McLeod, III commented that you’d have to view for 12 hours at the most to be able to witness the shower. (Jenniskens)

Brightest Stars in Ursa Minor sorted by decreasing luminosity

Name

RA

DEC

Mag

Distance

Spectral class

Polaris α

02h 31m 47.08s

+89° 15′ 50.9″

431

1.97 ly

F7:Ib-IIv SB

Β UMi

14h 50m 42.40s

+74° 09′ 19.7″

126

2.07 ly

K4IIIvar

γ UMi

15h 20m 43.75s

+71° 50′ 02.3″

480

3.04 ly

A3II-III

ε UMi

16h 45m 58.16s

+82° 02′ 14.1″

346

4.21 ly

G5IIIvar

5 UMi

14h 27m 31.52s

+75° 41′ 45.4″

345

4.25 ly

K4III

ζ UMi (*)

15h 44m 03.46s

+77° 47′ 40.2″

376

4.29 ly

A3Vn

δ UMi

17h 32m 12.90s

+86° 35′ 10.8″

183

4.35 ly

A1Vn

RR UMi

14h 57m 35.12s

+65° 55′ 56.6″

398

4.63 ly

M5III

4 UMi

14h 08m 51.01s

+77° 32′ 50.8″

500

4.80 ly

K3III

η UMi

16h 17m 30.50s

+75° 45′ 16.9″

97

4.95 ly

F5V

θ UMi (#)

15h 31m 25.05s

+77° 20′ 57.6″

832

5.00 ly

K5III

11 UMi

15h 17m 05.88s

+71° 49′ 26.0″

389

5.02 ly

K4III

HD 136064

15h 14m 38.00s

+67° 20′ 51.6″

83

5.15 ly

F9IV

HD 124730

14h 12m 04.05s

+69° 25′ 57.6″

445

5.18 ly

M2III

19 UMi (^)

16h 10m 49.53s

+75° 52′ 39.1″

665

5.48 ly

B8V

HD 118904

13h 37m 11.05s

+71° 14′ 32.2″

400

5.50 ly

K2III

HD 149681

16h 25m 43.53s

+78° 57′ 49.0″

138

5.55 ly

F0V

HD 133002

14h 50m 19.63s

+82° 30′ 45.0″

141

5.63 ly

F9V

HD 140227

15h 37m 39.21s

+69° 16′ 59.6″

881

5.65 ly

M0III

HD 145622

16h 03m 31.40s

+76° 47′ 38.0″

581

5.73 ly

A3V

*will die first #will die last ^most like our sun (Wikipedia)

Bibliography

Image Source by order (couldn't add under picture)

1. Dolan, Chris. “Ursa Minor.” Ursa Minor, www.astro.wisc.edu/~dolan/constellations/constellations/Ursa_Minor.html.

2. “Ursa Minor Constellation Map.” Constellation Guide Constellations: A Guide to the Night Sky, Sky&Telescope Magazine, www.constellation-guide.com/constellation-list/ursa-minor-constellation/.

3. Sky, Earth. “Polaris Big Dipper Little Dipper.” Polaris the Present Day North Star, EarthSky, 22 May 2017, en.es-static.us/upl/2010/07/polaris_big_dipper_little_dipper.jpg.

4. Sites, Google. “Ursa Minor.” Constellations & Mythology, sites.google.com/site/rzconstellationmythology/ursa-minor.

5. NASA. NGC 6217. NASA, commons.wikimedia.org/wiki/File:NGC_6217_hs-2009-25-bc-full_jpg.jpg.

Text Citations

1. Mythology of the Constellation Ursa Minor, www.heavens-above.com/myth.aspx?lat=46.5513&lng=24.5572&loc=Targu Mures&alt=312&tz=EET&cul=en&con=UMi.

2. Bergh, Sidney Van den. The Galaxies of the Local Group. Cambridge University Press, 2007.

3. “Constellation Guide.” Constellation Guide, www.constellation-guide.com/constellation-list/ursa-minor-constellation/.

4. Jenniskens, Peter. “Comet and Meteoroid Orbits.” Meteor Showers and Their Parent Comets, pp. 58–68., doi:10.1017/cbo9781316257104.006.

5. “List of Stars in Ursa Minor.” Wikipedia, Wikimedia Foundation, 30 Nov. 2018, en.wikipedia.org/wiki/List_of_stars_in_Ursa_Minor.

6. Rao, Joe. “The North Star: Polaris.” Space.com, Space Created with Sketch. Space, 16 May 2017, www.space.com/15567-north-star-polaris.html.

7. “SIMBAD Query Result.” SIMBAD Astronomical Database - CDS (Strasbourg), simbad.u-strasbg.fr/simbad/sim-id?protocol=html&Ident=QSO B1637 826.

8. SOCIETY, ROYAL ASTRONOMICAL. MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY. FORGOTTEN BOOKS, 2015.

9. Sun, Xiaochun, and Jacob Kistemaker. The Chinese Sky during the Han: Constellating Stars and Society. Brill, 1997.

10. “Use the Big Dipper to Find the Little Dipper.” EarthSky, earthsky.org/tonight/use-big-dipper-to-find-polaris-and-little-dipper.