Little Bear
The Ursa Minor is a constellation in the northern hemisphere. It shares the same name as the Big Dipper, because its tail resembles the handle of a spoon: it consists of seven stars in the shape of a car; four of them form what is the deep part of the car and the other three are the handle of the car. It was one of the 48 constellations originally enumerated by the astronomer Claudius Ptolemy in the II century, and has since been one of the 88 contemporary constellations.
The best-known element of Ursa Minor is the polar star, called Polaris, which is located approximately in the extension of the Earth's axis, so that it remains almost fixed in the sky and marks the geographic north pole, which is why it has been used by sailors as a reference point on their journeys. Given its location, the Little Dipper can only be seen in the northern hemisphere, but instead, in that hemisphere it is seen all year round. Along with the Big Dipper, it is one of the most characteristic elements of the firmament of the northern hemisphere.
Notable features
Polaris (α Ursae Minoris) is the brightest star in the constellation. Distant about 432 light years from Earth, it is a yellow-white supergiant that varies between spectral type F7Ib and F8Ib, being the most prominent Cepheid variable in the sky. It is a triple star system: the supergiant is accompanied by two main sequence stars of type F7V and F3V separated by 17 and 2400 AU from it.
Kochab (β Ursae Minoris), the second brightest star, is an orange giant of type K4III; It is orbited by a giant exoplanet at 1.4 AU. Next in brightness is γ Ursae Minoris, called Pherkad, a white giant of spectral type A2III 11,000 times more luminous than the Sun. It is a Delta Scuti variable with a period of 3.43 hours. ζ Ursae Minoris is a white star of the main sequence evolving to the giant phase, since its luminosity —227 times higher than the solar one— is abnormally high. Likewise, δ Ursae Minoris, known as Yildun, is also a white main sequence star, of type A1Van, whose mass is 2.35 times greater than that of the Sun.
11 Ursae Minoris is a type K4III giant with a planet that takes 516 days to complete one orbit around it. Another star where an exoplanet has been discovered is Baekdu, the official name of 8 Ursae Minoris.
T Ursae Minoris is a red giant that oscillates between spectral type M4e and M6e, currently cataloged as a long-period semiregular variable, whose brightness fluctuates between magnitude 7.8 and 15; it is notable that having been observed since 1905, until 1979 behaved like a Mira variable, but later its period decreased to 229 days, decreasing at a rate of 3.8 days per cycle. Another variable in the constellation is RR Ursae Minoris, a red giant and semiregular variable whose maximum brightness reaches +4.53. It is also a spectroscopic binary whose orbital period is 748.9 days.
In this constellation is located 1RXS J141256.0+792204, informally known as Calvera, a solitary neutron star that is not part of a star system. At an uncertain distance between 250 and 1,000 light-years, it is one of the closest objects of its kind to Earth. With an age—as a stellar remnant—of 285,000 years, its temperature is greater than 750,000 K.
The Little Dipper contains few relevant deep-sky objects. Among them is NGC 6217, a barred spiral galaxy 67 million light years away. Much closer, about 225,000 light-years distant from Earth, the Ursa Minor Dwarf is a dwarf spheroidal galaxy discovered by Albert George Wilson in 1955.
Main Stars
- α Ursae Minoris (Polaris, Polar Star or North Star), the brightest star of the constellation, a yellow supergigant and scavenged variable of magnitude 1.97.
- β Ursae Minoris (Kochab), of magnitude 2,07, an orange giant star that was formerly used as a polar star.
- γ Ursae Minoris (Pherkad), of magnitude 3,00, white and variable star of the Delta Scuti type.
- δ Ursae Minoris (Yildun or Pherkard), white star of the main sequence of magnitude 4.35.
- ε Ursae Minoris, binaria eclipsante and variable RS Canum Venaticorum of magnitude 4,21.
- ج Ursae Minoris (Alifa al Farkadain), a white star of magnitude 4.32.
- η Ursae Minoris (Anwar al Farkadain), white-yellow dwarf of magnitude 4,95.
- λ Ursae Minoris, red giant of magnitude 6.38.
- 5 Ursae Minoris, orange giant of magnitude 4,25, fifth brightest star in constellation.
- 11 Ursae Minoris, an orange giant with an extrasolar planet.
- 24 Ursae Minoris, star Am of magnitude 5.77.
- RR Ursae Minoris, red giant and semi-regular variable; its brightness varies between magnitude 4.53 and 4.73.
- Calvera, an informal name that you think can be the neutron star closest to Earth.
Deep Sky Objects
- NGC 6217, spiral galaxy of surface brightness 14 and apparent size 3.6' x 3.6'.
- NGC 5832, coiled spiral galaxy smaller than the previous one.
- Enana Galaxy of the Osa Menor, belonging to the Local Group and located 4.5o south of Pherkad (γ Ursae Minoris).
Mythology
In Greek mythology, there are several versions of the origin of the Little Dipper. One of them would be Phoenice, transformed into a bear by Artemis after being seduced by Zeus. This story is very similar to that of Callisto, who was catasterized in the Big Dipper and for this reason some authors believe that originally there must have been a story with two catasterisms of the same character (Zeus would have turned Callisto into the Big Dipper and later Artemis would have turned her into the Big Dipper). turned into the Little Dipper).
In another version it is said that it was Cinosura, nurse of Zeus and nymph of Mount Ida.
It is also said that he was the son of Callisto, after hunting down his own mother, who were catasterized by petition to Zeus.