Mizar

Proper names: Mizar, 79 Ursae Majoris, Zeta Ursae Majoris, The Horse
Catalog numbers:
Bonner Durchmusterung (BD) +55°1598, Hipparcos Input Catalog (HIC) 65378, Aitken Double Star (ADS) 8891, Fifth Fundamental Catalogue (FK5) 497, New Suspected Variable (NSV) 6224
Heavy element abundance: 100% of Sol
Source for heavy element abundance: Strobel [Fe/H] Determinations
Arity: quarternary (!)
Points of interest:
The gaps between the two A stars and their orbital period have both been accurately measured. However, only the orbital period of the two B stars, and the gap between the A and the B star, are reliable numbers. The Ba-Bb gaps and the A-B period are probably in error. If these numbers are to be believed, they indicate that the two B stars have a total mass of over 130 suns, and the whole system of four stars have a total mass in excess of 13 000 x Sol!

Right Ascension and Declination: 13h23m55.539s, +54°55'31.38" (epoch 2000.0)
Distance from Sol: 78.2 light-years (24.0 parsecs)
Standard error in distance: 1.4407%
Source for distance: Hipparcos
Celestial (X,Y,Z) coordinates in ly: -41.9, -16.1, 64.0
Galactic (X,Y,Z) coordinates in ly: -14.1, 34.2, 68.9
Proper motion: 0.121 arcsec/yr (102.0° from north)
Radial Velocity: -5.6 km/sec
Source for proper motion and radial velocity: Gliese
Galactic (U,V,W) velocity components in km/s: 13.3, 3.65, -5.45

What do all these fields mean?

Data for Aa and Ab's orbit around one other:
Combined spectrum: A1p V
Combined apparent visual magnitude: +2.25
Combined absolute visual magnitude: +0.35
Combined visual luminosity: 63.0 x Sol
Period: 20.454 days
Semimajor Axis: 0.29 A.U.s
Eccentricity: 0.53
Periastron distance: 0.14 A.U.s
Apastron distance: 0.44 A.U.s
Year in which periastron occurs: 1927.44
Source for orbit data: H.N. Russell
Comfort Zone (visual) around both: 7.94 A.U.s

Data for Ba and Bb's orbit around one other:
Combined spectrum: A1m
Combined apparent visual magnitude: +3.95
Combined absolute visual magnitude: +2.05
Combined visual luminosity: 13.2 x Sol
Period: 57 years
Semimajor Axis: 3.12 A.U.s
Source for orbit data: Gliese

Data for (Aa-Ab) and (Ba-Bb)'s orbit around one other:
Combined absolute visual magnitude: +0.15
Combined visual luminosity: 76.1 x Sol
Observed Separation: 345 A.U.s
As seen from (Aa-Ab):
(Ba-Bb) would appear as magnitude -16.83
As seen from (Ba-Bb):
(Aa-Ab) would appear as magnitude -18.53

Component Aa:
Catalog numbers:
Henry Draper (HD) 116656, Smithsonian Astrophysical Observatory (SAO) 28737, Hoffleit Bright Star (HR) 5054
Mass: 7.7 x Sol
Diameter: 4.12 x Sol
Source for diameter: Apparent Diameters and Absolute Radii of Stars (Fracassini+ 1988)

Component Ab:
Catalog numbers:
Henry Draper (HD) 116656, Smithsonian Astrophysical Observatory (SAO) 28737, Hoffleit Bright Star (HR) 5054

Component Ba:
Catalog numbers:
Henry Draper (HD) 116657, Smithsonian Astrophysical Observatory (SAO) 28738, Hoffleit Bright Star (HR) 5055
Right Ascension and Declination: 13h23m56.4s, +54°55'18" (epoch 2000.0)
Celestial (X,Y,Z) coordinates in ly: -41.9, -16.1, 64.0
Galactic (X,Y,Z) coordinates in ly: -14.1, 34.2, 68.9
Proper motion: 0.119 arcsec/yr (106.0° from north)
Radial Velocity: -9.3 km/sec
Source for proper motion and radial velocity: Gliese
Galactic (U,V,W) velocity components in km/s: 14.1, 1.18, -8.25
Diameter: 3.89 x Sol
Source for diameter: Apparent Diameters and Absolute Radii of Stars (Fracassini+ 1988)

Component Bb:
Catalog numbers:
Henry Draper (HD) 116657, Smithsonian Astrophysical Observatory (SAO) 28738, Hoffleit Bright Star (HR) 5055
Right Ascension and Declination: 13h23m56.4s, +54°55'18" (epoch 2000.0)
Celestial (X,Y,Z) coordinates in ly: -41.9, -16.1, 64.0
Galactic (X,Y,Z) coordinates in ly: -14.1, 34.2, 68.9
Proper motion: 0.119 arcsec/yr (106.0° from north)
Radial Velocity: -9.3 km/sec
Source for proper motion and radial velocity: Gliese
Galactic (U,V,W) velocity components in km/s: 14.1, 1.18, -8.25

Data for this star system were most recently updated on 4-April-2001.