| Betelgeuse (Betelgeux; Alpha Orionis; a Ori) |
|
A red supergiant M star, one of the largest known.
By means of speckle interferometry and
other interference techniques, the star's diameter has been measured directly and found to
be about 1,000 times that of the Sun . The presence of large bright "star-spots" has also
been revealed. Ultraviolet observations made with the Hubble Space Telescope showed
Betelgeuse to be surrounded by an extended chromosphere. Its mass is about twenty
times the Sun's. The brightness varies irregularly between magnitudes 0.4 and 0.9 with
a rough period of around five years. See also: Table 3. |