Monthly Constellation - Ursae Minoris

During the light summer months here in the north there is not much observing going on, so I thought I'd start a Monthly Constellation series concentrating on the constellations visible from latitude 60 degrees North. The idea is to provide general information about the constellation and possible targets for amateur astronomers. An other reason is to familiarize my self with the constelleations, so this is also a learning process for me. The info and targets are under no circumstances complete. The reader can find lots of additional information by searching the Web.

Ursa Minor (Little Bear)

Ursa Minor is a constellation everybody is more or less familiar with, beacuse it contains Polaris (the North Star). Some people might not be aware that the constellation itself looks like a smaller version of the Big Dipper asterism. From urban skies the constellation can be hard discern, because it is mostly comprised of stars of magnitude ~2 - 5. However from areas with darker skies the Little Bear is easy to spot circling around the north celestial pole.

Ursae Minoris

Polaris is not exactly at the north celestial pole, but little less than 1 degree removed. Polaris was once used as the standard candle for determining stellar magnitudes, but then it was discovered that it is infact a variable star and therefore not a very good standard candle. In addition to being a variable star Polaris is also a binary star.

Even though being rather poor in obervational targets, there are a few that you can take a look at.

Binary Stars
Polaris (Alpha (α) Ursae Minoris): A combination of magnitude 2 and 9 stars, with a separation of 19 arcseconds. Even though usually designated as a binary star Polaris is infact a multiple star system composed of 4 stars in addition to Polaris itself. The components of the system are Alpha Urase Minoris A, Ab, B, C and D.

Epsilon (ε) Ursae Minoris: A triple star system composed of Epsilon Ursae Minoris A, which is a spectroscopic binary and component B located 77 arcseconds away. Being a spectroscopic binary, component A can not be resolved with optical means only via spectral analysis of the dopplershifts of the components. This triple is the third star on the handle of the Little Dipper starting from Polaris.

NGC 6217: A face-on barred spiral of which the Hubble Space Telescope has taken a grand image. This galaxy can be difficult to find visually having a low surface brightness of magnitude 11.2 and angular size of 3,3 arcminutes compared to the Andromeda Galaxy's 3.5 and almost 3 degrees. Due to the low brightness it is mainly a photographic target (unless you happen to own a really big light bucket). If you have a equatorial mount without GOTO the galaxy can be found by first finding Zeta Ursae Minoris, the star joining the bowl and handle of the dipper, then rotating West in RA 48 minutes. This should land the galaxy in the field of view. The difference in declination is only 24'.

NGC 6217 location

That's about it for Ursa Minor.

Clear Skies


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