Beta Monocerotis
Beta Monocerotis is a triple star system in the constellation of Monoceros. To the naked eye, it appears as a single star with an apparent visual magnitude of approximately 3.74, making it the brightest visible star in the constellation. A telescope shows a curved line of three pale blue stars. William Herschel who discovered it in 1781 commented that it is "one of the most beautiful sights in the heavens". The star system consists of three Be stars, β Monocerotis A, β Monocerotis B, and β Monocerotis C. There is also an additional visual companion star that is probably not physically close to the other three stars.
System
The three stars of β Monocerotis lie approximately in a straight line. Component B is 7" from component A, and component C a further 3" away. The stars have a common proper motion across the sky and very similar radial velocities. They share a single Hipparcos satellite identifier and are assumed to be at the same distance, around 700 light years based on their parallax.β Monocerotis is classified as a variable star, although it is unclear which of the three components causes the brightness changes. The magnitude range is given as 3.77 to 3.84 in the Hipparcos photometric band.