Designations
- Bayer: α UMi
- Flamsteed: 1 UMi
- Hipparchos: HIP 11767
Data
- Constellation: Ursa Minor
- Apparent Magnitude: 1.86-2.13
- Variable Type: δ Cephei
- Right Ascension (J2000): 2h31m38.82s
- Declination (J2000): +89°15'31".0
- Colour Index (B-V): 0.60
- Distance: 432.73±6.32ly
Description
Despite not being particularly bright at an average magnitude of around 2, Polaris is an important star in the modern day for those in the Northern Hemisphere. Its position less than a degree from the North Celestial Pole makes it especially useful for orienting oneself during nighttime.
To locate Polaris, it is common to use two sets of pointer star asterisms, the set chosen depending on the time of year and latitude. For those near the North Pole, the Great Pointers, the stars Merak (β) & Dubhe (α) UMa, are available throughout the year to be used to find Polaris (although, at the North Pole, one only need look straight up at Zenith to locate it). To use these stars, make a line starting at Merak, then continue it through and past Dubhe. This line will eventually arrive at Polaris. To assist in remembering this asterism, one may use the mnemonic, "From Merak, we smoke a Dubhe on the way to Polaris!" However, at lower latitudes these stars might set too low on the horizon to be seen during certain parts of the year. In this case, there is, conveniently, another set of pointers roughly opposite Merak & Dubhe across the North Celestial Pole. The Three Guides, composed of Algenib (γ Peg), Alpheratz (α And), & Caph (β Cas), all lie roughly along a meridian line and thus may be used to point north. Drawing a line from Algenib through Alpheratz and continuing through Caph, one will eventually arrive at Polaris. There isn't a common mnemonic to remember these stars by, but one could possibly use "All Aardvarks Consume Pants."
Nomenclature
Stella Polaris
From the time of the ancient Egyptians, the North Celestial Pole precessed from the star Thuban through the head of Camelopardalis to the where it is today, right by α UMi. However, it was not until the early Renaissance that the pole ventured close enough to for α UMi to be called the polestar. Alfonsine Tables (1492) was the first time that the Latin name Stella Polaris, 'star of the pole', was attested in literature, which then propagated throughout globes, atlases, and catalogues not long after. The modern form Polaris is an abbreviation of the original name, and simply means 'of the pole.' The North Celestial Pole will make its closest approach to Polaris around the year 2100AD to under half a degree, after which it will make its way over to Errai and then Alderamin, both in Cepheus.
Some Greek authors, notably Ps-Eratosthenes, mentioned the name Πόλος Polus for some star in the region of Ursa Minor. While it would make sense to apply this name to α UMi in the modern day, due to the effects of precession, this name certainly must have had to refer to another, much dimmer star such as HIP 62572 in Camelopardalis or 4 UMi. Neither star was especially close to the pole, but they were certainly the brightest naked-eye star nearby.
Alrucaba
Kunitzsch and Smart (2006) mentioned the name for this star. The name is from Arabic al-Rukba, 'the knee [of the Great Bear]', a title for θ UMa from its location within the figure which was later misapplied to α UMi in late medieval times. It may have also been misapplied to β UMi as well (see Kochab).
Yilduz
A name from Turkish yıldız, 'star', a generic term erroneously considered to be a name for α UMi by Renaissance scholars. In modern times, the name was misspelt and misapplied to the star δ UMi as Yildun.
Stella Maris
An occasional Christian title for the star was the Latin Stella Maris, 'star of the sea'. First attested in the medieval writings of Saint Jerome, it was originally an alternative name for the Mother Mary, possibly a bastardisation of her Hebrew name Miriam. As Mary and α UMi were both guiding figures to Christian sailors, the name came to be one for the star as well, a quite fitting association given the meaning of Stella Maris.
Tramontana
A name that may be familiar to those of the Mediterranean, the Romans referred to anything northerly as trānsmontānus, 'beyond, or across the mountains' (for them, this meant across the Alps). The name evolved into various forms across the Vulgar Latin-speaking regions of the empire, such as the Italian Tramontana, from which we get the alternative name for the northerly α UMi.
Cynosura
Following the tradition of naming a lucida after its constellation, the star took on the Greek name Κυνόσουρα Cynosura, a common alternative name for Ursa Minor. The name is that of one of the Idaean nymphs of Zeus who nursed him on honey and the milk of the she-goat Αμαλθεια Amalthea (see also, Capella). On one occasion, she and her sister Ἑλικη Helice, also a nurse of the future King of the Gods, were transformed into bears while Zeus transformed himself into a dragon to hide from his father Cronus. To honour them for their efforts, Zeus placed the sisters into the sky as the celestial bears, Cynosura as Ursa Minor and Helice as Ursa Major.
Phoenice
Another name for the constellation applied to its lucida, Φοινίκη Phoenice was a Greek term for the constellation that alluded to the cultural transmission of usage of the constellation for navigation from the Phoenicians to the Greeks. Aratus in Phaenomena stated that the Greeks originally used Ursa Major to orient themselves northwards, while the Phoenicians used Ursa Minor. Hyginus in Astronomica stated that Thales of Miletus, a Phoenician by birth, introduced the navigational aid to the Greeks.
Al Juday
Variously spelt as al-Ğudayy and al-Ğady, the name means 'the kid', but technically denoted some sort of human figure. Al Juday was part of the ind-Arab scene of the Mourning Maidens, and was the accused killer of their father (see Āl Naʽš). He was pursued in the night sky by al-Ḥāğizān, 'the two mediators', represented by β & γ UMi. In antiquity when this scene was first imagined, the North Celestial Pole lay between Polaris and Kochab in Camelopardalis, and so the scene of Al Juday in flight made much more sense as he could be seen circling the pole.
Alsamiya
An alternative ind-Arab name for α UMi, al-Samiyā means 'the height, or emminent', alluding to the star being the closest to the North Celestial Pole, or the top of the sky.
Mismar
Derived from Arabic al-Mismar, 'the nail', the name alludes to α UMi's fixedness in the night sky.
Sources
- IAU WGSN. IAU-Catalog of Star Names (CSN). link.
- Stellarium Contributors. Stellarium Astronomy Software. link.
- Ridpath, Ian. Star Tales. link.
- Kunitszch, Paul. Smart, Tim. A Dictionary of Modern Star Names (2006), pp. 58. link.
- Allen, Richard Hinckley. Star Names - Their Lore and Meaning (1899), pp. 452-453. link.
- Grant, Mary. The Myths of Hyginus (1960). link.
- Condos, Theony. Star Myths of the Greeks and Romans: A Sourcebook (1997), pp. 201-204. link.
- Hard, Robin. Eratosthenes and Hyginus, Constellation Myths with Aratus's 'Phaenomena' (2015), pp. 56-61, 295. link.
- Kidd, Douglas. Aratus: Phaenomena (1997), pp. 75. link.
- Gain, D. B. The Aratus Ascribed to Germanicus Caesar (1976), pp. 53-54. link.
- Lafitte, Roland. Catalogue of Star Names of the Arabian Traditional Sky. link.