The star Alpha Orionis, the tenth-brightest star in the sky. It is an M1 or M2 supergiant and a semiregular variable, fluctuating between magnitudes 0.0 and 1.3 in a period of several years, with an average magnitude of 0.4. It lies around 500 l.y. away, much closer than the stars in the Orion Association, and has a luminosity 10 000 times the Sun’s. Betelgeuse is extremely large, about 500 times the diameter of the Sun. Its variations in brightness occur as it swells and contracts in size.
http://hubblesite.org/image/1447/news_release/2004-04
- Opportunity
- opportunity cost
- opportunity sampling
- opposite angles
- opposites
- opposite side
- opposition
- opposition effect
- oppression
- opsin
- opsonin
- opsonization
- optical activity
- optical ammeter
- optical axis
- optical brightener
- optical card
- optical centre
- optical character reader
- optical character recognition
- optical computing
- optical continuity
- optical density
- optical depth
- optical disk