Ursa Minor

Ursa Minor has traditionally been important for navigation, particularly by mariners, because of Polaris being the north pole star.

Beta Ursae Minoris, also known as Kochab, is an aging star that has swollen and cooled to become an orange giant with an apparent magnitude of 2.08, only slightly fainter than Polaris.

[5] According to Diogenes Laërtius, citing Callimachus, Thales of Miletus "measured the stars of the Wagon by which the Phoenicians sail".

Diogenes identifies these as the constellation of Ursa Minor, which for its reported use by the Phoenicians for navigation at sea were also named Phoinikē.

[10] Instead, the mythographic tradition of Catasterismi makes Cynosura the name of an Oread nymph described as a nurse of Zeus, honoured by the god with a place in the sky.

One suggestion connects it to the myth of Callisto, with her son Arcas replaced by her dog being placed in the sky by Zeus.

[13] An alternative myth tells of two bears that saved Zeus from his murderous father Cronus by hiding him on Mount Ida.

Polaris can also be found by following a line through the two stars—Alpha and Beta Ursae Majoris, popularly called the Pointers—that form the end of the "bowl" of the Big Dipper, for 30 degrees (three upright fists at arms' length) across the night sky.

[20] The official constellation boundaries, as set by Belgian astronomer Eugène Delporte in 1930, are defined by a polygon of 22 segments (illustrated in infobox).

[21][c] The traditional names of the main seven in Johann Bayer's ordering are: Marking the Little Bear's tail,[15] Polaris, or Alpha Ursae Minoris, is the brightest star in the constellation, varying between apparent magnitudes 1.97 and 2.00 over a period of 3.97 days.

[25] Traditionally called Kochab, Beta Ursae Minoris, at apparent magnitude 2.08, is slightly less bright than Polaris.

[26] Located around 131 light-years away from Earth,[27][d] it is an orange giant—an evolved star that has used up the hydrogen in its core and moved off the main sequence—of spectral type K4III.

[26] Slightly variable over a period of 4.6 days, Kochab has had its mass estimated at 1.3 times that of the Sun via measurement of these oscillations.

[30] Traditionally known as Pherkad, Gamma Ursae Minoris has an apparent magnitude that varies between 3.04 and 3.09 roughly every 3.4 hours.

[34] Also possibly a member of this class is Zeta Ursae Minoris,[35] a white star of spectral type A3V,[36] which has begun cooling, expanding and brightening.

Located 860 ± 80 light-years distant,[39] it is an orange giant of spectral type K5III that has expanded and cooled off the main sequence, and has an estimated diameter around 4.8 times that of the Sun.

Just over 3.5 degrees from the north celestial pole, Delta is a white main-sequence star of spectral type A1V with an apparent magnitude of 4.35,[42] located 172±1 light-years from Earth.

[43] A triple star system,[44] Epsilon Ursae Minoris shines with a combined average light of magnitude 4.22.

[44] Located close to Polaris is Lambda Ursae Minoris, a red giant of spectral type M1III.

[47] Located south of Kochab and Pherkad towards Draco is RR Ursae Minoris,[32] a red giant of spectral type M5III that is also a semiregular variable ranging from magnitude 4.44 to 4.85 over a period of 43.3 days.

[55] RW Ursae Minoris is a cataclysmic variable star system that flared up as a nova in 1956, reaching magnitude 6.

[59] WD 1337+705 is a cooler white dwarf that has magnesium and silicon in its spectrum, suggesting a companion or circumstellar disk, though no evidence for either has come to light.

It has a planet 4.5 times the mass of Jupiter, with one of the most eccentric planetary orbits (e = 0.66), discovered by precisely measuring the radial velocity of the star in 2013.

[65] A further study published in 2012 showed that it has a companion around 2.7 times as massive as Jupiter that takes around 16 years to complete an orbit and is 6.8 AU distant from its star.

Ursa Minor, with Draco looping around it, as depicted in Urania's Mirror , [ 4 ] a set of constellation maps published in London c. 1825
Ursa Minor as depicted in The Book of Fixed Stars , ca. 1009-1010. Unlike in western representations, the bear is drawn with its tail drooping down.
The constellation Ursa Minor as it can be seen by the naked eye (with connections and label added). Notice the seven stars of Ursa Major that form the Big Dipper and then make a line from the outermost Big Dipper stars (sometimes called the "pointers") to Polaris.
Ursa Minor and Ursa Major in relation to Polaris
NGC 6217