Dubhe (Alpha Ursae Majoris) is a blue to white main sequence dwarf star that can be located in the constellation of UrsaMajor. It is the 35th brightest star in the night sky. Alpha Ursae Majoris is the Bayer Classification for the star. The Id of the star in the Yale Bright Star Catalogue is HR4301. HIP54061 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD95689. Dubhe has alternative name(s), 50 Ursae Majoris , 50 UMa. In Arabic, it is known as Ad-Dubb. Dubhe is a multiple star system with 2 stars orbiting in its solar system.
Dubhe might have the honour of the Alpha Flamesteed classification, it is not the brightest star in the constellation of Ursa Major, the Big Bear. The brightest star in the constellation is in fact Alioth which is on the tail of the bear. It has a companion star which is 23 times as far from the main star as the Earth is to our Sun. It takes about 44.4 years to orbit round the master star. 1
The location of the star in the galaxy is determined by the Right Ascension (R.A.) and Declination (Dec.), these are equivalent to the Longitude and Latitude on the Earth. The Right Ascension is how far expressed in time (hh:mm:ss) the star is along the celestial equator. If the R.A. is positive then its eastwards. The Declination is how far north or south the star is compared to the celestial equator and is expressed in degrees. For Dubhe, the location is 11h 03m 43.84 and +61d45`04.0 .
All stars like planets orbit round a central spot, in the case of planets, its the central star such as the Sun. In the case of a star, its the galactic centre. The constellations that we see today will be different than they were 50,000 years ago or 50,000 years from now. Proper Motion details the movements of these stars and are measured in milliarcseconds. The star is moving -034.70 ± 000.31 towards the north and -134.11 ± 000.48 east if we saw them in the horizon.
Luminosity is the amount of energy that a star pumps out and its relative to the amount that our star, the Sun gives out. The figure of 2.0000000 that I have given is based on the Spectral Types page that I have found on the Internet. You might find a different figure, one that may have been calculated rather than generalised that I have done. The figure is always the amount times the luminosity of the Sun. It is an imprecise figure because of a number of factors including but not limited to whether the star is a variable star and distance.
Dubhe has a spectral type of F7V comp. This means the star is a blue to white main sequence dwarf star. The star has a B-V Colour Index of 1.06 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 4,736 Kelvin.
Dubhe has been calculated as 22.81 times bigger than the Sun.The Sun's radius is 695,800km, therefore the star's radius is an estimated 15,869,931.26.km.
Dubhe has an apparent magnitude of 1.81 which is how bright we see the star from Earth. Apparent Magnitude is also known as Visual Magnitude. If you used the 1997 Parallax value, you would get an absolute magnitude of -1.08 If you used the 2007 Parallax value, you would get an absolute magnitude of -1.07. Magnitude, whether it be apparent/visual or absolute magnitude is measured by a number, the smaller the number, the brighter the Star is. Our own Sun is the brightest star and therefore has the lowest of all magnitudes, -26.74. A faint star will have a high number.
Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 26.38 which gave the calculated distance to Dubhe as 123.64 light years away from Earth or 37.91 parsecs. It would take a spaceship travelling at the speed of light, 123.64 years to get there. We don't have the technology or spaceship that can carry people over that distance yet.
In 2007, Hipparcos data was revised with a new parallax of 26.54 which put Dubhe at a distance of 122.90 light years or 37.68 parsecs. It should not be taken as though the star is moving closer or further away from us. It is purely that the distance was recalculated.
The source of the information if it has a Hip I.D. is from Simbad, the Hipparcos data library based at the University at Strasbourg, France. Hipparcos was a E.S.A. satellite operation launched in 1989 for four years. The items in red are values that I've calculated so they could well be wrong. Information regarding Stellar Age, Metallicity or Mass is from the E.U. Exoplanets. The information was obtained as of 12th Feb 2017.
|Short Name||50 UMa|
|English Meaning||The bear|
|Bayer Designation||Alpha Ursae Majoris|
|Alternative Name(s)||50 Ursae Majoris|
|Hipparcos Library I.D.||54061|
|Yale Bright Star Catalogue (HR) Id||4301|
|Bonner Durchmusterung||BD+62 1161|
|Henry Draper Designation||95689|
|Star Type||main sequence dwarf star|
|Absolute Magnitude||-1.08 / -1.07|
|Right Ascension (R.A.)||11h 03m 43.84|
|1997 Distance from Earth||26.38 Parallax (milliarcseconds)|
|123.64 Light Years|
|2007 Revised Distance from Earth||26.54 Parallax (milliarcseconds)|
|122.90 Light Years|
|Proper Motion Dec.||-34.70 ± 0.31 milliarcseconds/year|
|Proper Motion RA.||-134.11 ± 0.48 milliarcseconds/year|
|Spectral Type||F7V comp|
|Brightest in Night Sky||35th|
|Colour||(F) blue to white|
|Stars in Solar System||2|
|Radius (x the Sun)||22.81|
|Luminosity (x the Sun)||2.0000000|
|Calculated Effective Temperature||4,736 Kelvin|
The star has been identified as being a multi-star system, one in which there is at least one star in close orbit to another star or two or more stars orbiting a central point. The stars may be of equal mass, unequal mass where one star is stronger than the other or be in groups orbiting a central point which doesn't necessarily have to be a star. More information can be found on my dedicated multiple star systems page. The source of the info is Simbad. The file is dated 2000 so any differences between this and any other source will be down to the actual source from where the information came from.
|Proper Motion mas/yr|
|H.D. Id||B.D. Id||Star Code||Magnitude||R.A.||Dec.||Spectrum||Colour||Year|
The map was generated using Night Vision, an awesome free application by Brian Simpson.