- Epsilon Ursae Majoris
name=Epsilon Ursae Majoris Starbox image
caption=Alioth in Ursa Major. Starbox observe
ra=12h 54m 01.6s
dec=+55° 57′ 35.4″
Ursa MajorStarbox character
variable=alpha2-CVn Starbox astrometry
absmag_v=-0.22 Starbox detail
luminosity=108 | temperature=9,400
age=? Starbox catalog
names=Alioth, Allioth, Aliath, 77 Ursae Majoris, HR 4905, BD +56°1627, HD 112185, GCTP 2964.00, SAO 28553, FK5 483, CCDM 12540+5558, HIP 62956.
Epsilon Ursae Majoris (ε UMa / ε Ursae Majoris) is the brightest
starin the constellation Ursa Major(despite its Bayer designationbeing merely "epsilon"), and at magnitude 1.76 is the thirty-first brightest star in the sky. It also has the traditional name Alioth (from the Arabic word "alyat"—fat tail of a sheep).
It is known as 北斗五 (the Fifth Star of the Northern Dipper) or 玉衡 (the Star of Jade Sighting-tube) in Chinese.
It is the star in the tail of the bear closest to its body, and thus the star in the handle of the
Big Dipperclosest to the bowl. It is also a member of the large and diffuse Ursa Major moving group. Historically, the star was frequently used in celestial navigationin the maritime trade, because it is listed as one of the 57 navigational stars.ref label|1728|1|^
According to "
Hipparcos", Alioth is 81 light years (25 parsecs) from Earth. Its spectral typeis A0p; the "p" stands for peculiar, as the spectrum of its light is quite odd, of a kind characteristic of an Alpha2 Canum Venaticorum variable. Alioth, as a representative of this type, is believed to look the way it does because of two interacting processes: first, the star's strong magnetic fieldseparating different elements salting the star's hydrogenfuel, then a rotation axis at an angle to the magnetic axis spinning different bands of magnetically sorted elements into the line of sight between Alioth and the Earth. The intervening elements react differently at different frequencies of light as they whip in and out of view, causing Alioth to have very strange spectral lines that fluctuate over a period of 5.1 days. In the case of Alioth, the rotational and magnetic axes are at almost 90 degrees to one another; in the map of Alioth linked below, note how the darker (denser) regions of chromiumform a band at right angles to the equator.A recent study suggests the 5.1 days variation may be due to a substellar object with around 14.7 Jupiter masses in eccentric orbit (e=0.5) and average separation of 0.055 Astronomical units.
For its type, Alioth has a relatively weak magnetic field (15 times weaker than α CVn's), but it is still 100 times stronger than that of the Earth.
Stars and planetary systems in fiction
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