Editing Betelgeuse (section)

==Observation==

Recent visible-light observations of Betelgeuse have found the diameter to vary between 0.0568 and 0.0592 arcseconds.

Ultraviolet images show a bright patch indicating a higher temperature region, in this case on the southwestern portion of the star's surface. 

Visual observation have shown Betelgeuse's rotation axis has an inclination of about 20° to the direction of [[Earth]] and a position (or height) angle of about 55°. 

It is difficult to define the precise diameter of Betelgeuse as the photosphere has no "edge"—instead the gas making up the photosphere gets gradually thinner with distance from the star.

Betelgeuse has several features which are of particular interest to astronomers. Because of the size and proximity of this star it has the third largest angular diameter as viewed from Earth, smaller only than the Sun and R Doradus. Betelgeuse has a color index (B-V) of 1.86 and is has a mass of about 20 solar masses (Sol).

Betelgeuse's photosphere has an extended atmosphere which displays strong lines of emission (rather than absorption). This chromosphere has a temperature no higher than 5,500 K and may stretch outward to 7 times the diameter of the star. This extended gaseous atmosphere has been observed moving both away from and towards Betelgeuse, apparently depending on radial velocity fluctuations in the photosphere.