At magnitude 3.93, Alpha Monocerotis is the second-brightest star in Monoceros, the mythical Unicorn. However, the constellation's brightest star (β Mon) is actually a triple system, and α Mon is brighter than any component of β Mon - so it really deserves its Alpha designation.
The star's traditional name, Samoht, derives from a mythology much older than the constellation itself (which is fairly modern, invented in the 17th century). It is actually Egyptian, and refers to a long journey (possibly along the Nile), and translates into English roughly as "he who has travelled far."
Properties
Physically, α Mon is a yellow-orange class K0 III giant, at a distance of 144 light years. It radiates 60 times the luminosity of the Sun, from a relatively cool surface of 4815 K. The star's temperature and luminosity imply a radius 11 times solar, and a mass of 2.5 suns. With an age of about 1.4 billion years, the star ran out of core hydrogen fuel some 250 million years ago, and is now a stable helium-fusing giant, producing carbon and oxygen in its core. Like all stars of its kind, once the helium runs out, α Mon will expel its outer hydrogen envelope, and retire as a hot, dense white dwarf about the size of the Earth.
Alpha Mon's metal content is about 20% lower than the Sun's. The star is known for its spectral stability, and serves astronomers as a standard for determining the radial velocities of other giant stars that are not quite so well behaved.
[Adapted from STARS by Jim Kaler, Professor Emeritus of Astronomy, University of Illinois]