Beta Ursae Majoris
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| Observation data Epoch J2000.0 |
|
|---|---|
| Constellation (pronunciation) |
Ursa Major |
| Right ascension | 11h 01m 50.5s |
| Declination | +56° 22' 57" |
| Apparent magnitude (V) | +2.34 |
| Characteristics | |
| Spectral type | A1V |
| U-B color index | 0.01 |
| B-V color index | -0.02 |
| Variable type | suspected |
| Astrometry | |
| Radial velocity (Rv) | -12 km/s |
| Proper motion (μ) | RA: 81.66 mas/yr Dec.: 33.74 mas/yr |
| Parallax (π) | 41.07 ± 0.60 mas |
| Distance | 79 ± 1 ly (24.3 ± 0.4 pc) |
| Absolute magnitude (MV) | 0.41 |
| Details | |
| Mass | 3 M☉ |
| Radius | 2 R☉ |
| Luminosity | 69 L☉ |
| Temperature | 9800 K |
| Metallicity | ? |
| Rotation | ~39 km/s. |
| Age | ? years |
| Other designations | |
Beta Ursae Majoris (β UMa / β Ursae Majoris) is a star in the constellation of Ursa Major. It also has the traditional name Merak.
It is more familiar to northern hemisphere observers as one of the "pointer stars" in the Big Dipper, and a line connecting it with nearby Alpha Ursae Majoris (Dubhe) extends to Polaris, the north star. It is also one of the five stars in the Big Dipper asterism that form a part of a loose open cluster called the Ursa Major moving group, sharing the same area of space and not just the same patch of sky by our perspective.
Merak is fairly typical for a main sequence star of its type, although being slightly hotter and larger than our own Sun, it shines several times brighter than our home star. It is distinguished in the fact that evidence shows the star is surrounded by a cooling disk of dust, much like those discovered around Fomalhaut and most notably Vega. No planets have been discovered orbiting Merak, but the presence of the dust indicates they may exist or be in the process of forming.
The name is derived from the Arabic maraqq "loins" (of the bear).
