Editing Alioth (section)

==Physical characteristics==
[[Image:Sidney Hall - Urania's Mirror - Ursa Major.jpg|thumb|200px|left|Book plate by [[Sidney Hall]] depicting Ursa Major's stars]]
[[File:EpsUMaLightCurve.png|thumb|left|A [[light curve]] for Epsilon Ursae Majoris, plotted from ''[[TESS]]'' data<ref name=MAST/>]]

According to ''[[Hipparcos]]'', Epsilon Ursae Majoris is {{convert|81|ly|pc|abbr=off|lk=on}} from the [[Sun]]. Its [[spectral type]] is [[Ap and Bp stars|A1p]]; the "p" stands for ''[[Peculiar star|peculiar]]'', as its [[stellar spectrum|spectrum]] is characteristic of an [[Alpha2 Canum Venaticorum variable|α<sup>2</sup> Canum Venaticorum variable]]. Epsilon Ursae Majoris, as a representative of this type, may harbor two interacting processes: first, the star's strong [[magnetic field]] separating different elements in its [[hydrogen]] 'fuel'; second, a rotation axis at an angle to the magnetic axis may be spinning different bands of magnetically sorted elements into the line of sight between Epsilon Ursae Majoris and the Earth. The intervening elements react differently at different frequencies of light as they whip in and out of view, causing Epsilon Ursae Majoris to have very strange [[spectral line]]s that fluctuate over a period of 5.1 days. The ''kB9'' suffix to the spectral type indicates that the [[calcium]] K line is present and representative of a B9 spectral type even though the rest of the spectrum indicates A1.

Epsilon Ursae Majoris's rotational and magnetic poles are at almost 90 degrees to one another. Darker (denser) regions of [[chromium]] form a band at right angles to the equator.

It has long been suspected that Epsilon Ursae Majoris is a [[spectroscopic binary]], possibly with more than one companion.<ref name=morgan/>  A more recent study suggests Epsilon Ursae Majoris's 5.1-day variation may be due to a substellar object of about 14.7 [[Jupiter masses]] in an eccentric orbit (e=0.5) with an average separation of 0.055 [[astronomical unit]]s.<ref name="MNRASL385_1_L1"/>  It is now thought that the 5.1-day period is the rotation period of the star, and no companions have been detected using the most modern equipment.<ref name=shulyak/> Observations of Alioth with the [[Navy Precision Optical Interferometer]] also did not detect a companion.<ref name="npoi"/>

Epsilon Ursae Majoris has a relatively weak magnetic field for a variable of this type, 15 times weaker than [[α Canum Venaticorum]], but it is still 100 times stronger than [[Earth's magnetic field|that of the Earth]].<ref name=weakfield/>