Alioth (Epsilon Ursae Majoris) is a blue rotating star that can be located in the constellation of UrsaMajor. It is the 33rd brightest star in the night sky. Epsilon Ursae Majoris is the Bayer Classification for the star. The Id of the star in the Yale Bright Star Catalogue is HR4905. HIP62956 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD112185. Alioth has alternative name(s), 77 Ursae Majoris , eps_UMa, 77 UMa. In Arabic, it is known as Al-Jawn.
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 Alioth, the location is 12h 54m 01.63 and +55d57`35.4 .
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 -008.24 ± 000.15 towards the north and 111.91 ± 000.20 east if we saw them in the horizon.
Alioth has a spectral type of A0p. This means the star is a blue star. The star has a B-V Colour Index of -0.02 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 10,827 Kelvin.
Alioth has been calculated as 2.92 times bigger than the Sun.The Sun's radius is 695,800km, therefore the star's radius is an estimated 2,034,106.18.km.
Alioth has an apparent magnitude of 1.76 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 -0.21 If you used the 2007 Parallax value, you would get an absolute magnitude of -0.26. 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 40.30 which gave the calculated distance to Alioth as 80.93 light years away from Earth or 24.81 parsecs. It would take a spaceship travelling at the speed of light, 80.93 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 39.51 which put Alioth at a distance of 82.55 light years or 25.31 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 star is a rotating Alpha2 Canum Venaticorum variable type which means that its size changes over time. The Variable Type is usually named after the first star of that type to be spotted. Alioth brightness ranges from a magnitude of 2.000 to a magnitude of 2.000 over its variable period. The smaller the magnitude, the brighter the star. Its variable/pulsating period lasts for 5.0 days (variability).
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||eps UMa, 77 UMa|
|English Meaning||The black horse|
|Bayer Designation||Epsilon Ursae Majoris|
|Alternative Name(s)||77 Ursae Majoris|
|Hipparcos Library I.D.||62956|
|Yale Bright Star Catalogue (HR) Id||4905|
|Bonner Durchmusterung||BD+56 1627|
|Henry Draper Designation||112185|
|Absolute Magnitude||-0.21 / -0.26|
|Right Ascension (R.A.)||12h 54m 01.63|
|1997 Distance from Earth||40.30 Parallax (milliarcseconds)|
|80.93 Light Years|
|2007 Revised Distance from Earth||39.51 Parallax (milliarcseconds)|
|82.55 Light Years|
|Proper Motion Dec.||-8.24 ± 0.15 milliarcseconds/year|
|Proper Motion RA.||111.91 ± 0.20 milliarcseconds/year|
|Brightest in Night Sky||33rd|
|Variable Star Class||Rotating|
|Variable Star Type||Alpha2 Canum Venaticorum|
|Mean Variability Period in Days||5.000|
|Radius (x the Sun)||2.92|
|Calculated Effective Temperature||10,827 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.