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Alioth, Epsilon Ursae Majoris, 77 Ursae Majoris, HD112185, HIP62956, HR4905

Alioth (Epsilon Ursae Majoris) is a blue rotating star that can be located in the constellation of UrsaMajor. Alioth is the 33rd brightest star in the night sky and is the brightest star in Ursa Major based on the Hipparcos 2007 apparent magnitude. The star can be seen with the naked eye, that is, you don't need a telescope/binoculars to see it.

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), eps UMa. In Arabic, it is known as Al-Jawn.

Location of Alioth

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 +55d 57` 35.4 .

Proper Motion of Alioth

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 -8.24 ± 0.15 miliarcseconds/year towards the north and 111.91 ± 0.20 miliarcseconds/year east if we saw them in the horizon.

Physical Properties (Colour, Temperature, Radius) of Alioth

Alioth has a spectral type of A0p. This means the star is a blue star. The star is 7407.00000000 Parsecs from the Galactic Centre or terms of Light Years is 24158.9188900800000000s. 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 Radius has been calculated as being 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. However with the 2007 release of updated Hipparcos files, the radius is now calculated at being round 2.99. The figure is derived at by using the formula from SDSS and has been known to produce widely incorrect figures. The star's Iron Abundance is 0.00 with an error value of 9.99 Fe/H with the Sun has a value of 1 to put it into context.

Alioth Apparent and Absolute Magnitudes

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.

Distance to Alioth

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's Galacto-Centric Distance is 7,407.00 Parsecs or 24,158.92 Light Years. The Galacto-Centric Distance is the distance from the star to the Centre of the Galaxy which is Sagittarius A*.

Variable Type of Alioth

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 1.759 to a magnitude of 1.747 over its variable period. The smaller the magnitude, the brighter the star. Its variable/pulsating period lasts for 5.1 days (variability).

Source of Information

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 Metallicity and/or Mass is from the E.U. Exoplanets. The information was obtained as of 12th Feb 2017.

Alioth Facts

Alternative Names

Traditional/Proper NameAlioth
Flamsteed Name77 Ursae Majoris
Flamsteed Short Name77 UMa
Short Nameeps UMa
Arabic NameAl-Jawn
English MeaningThe black horse
Bayer DesignationEpsilon Ursae Majoris
Hipparcos Library I.D.62956
Yale Bright Star Catalogue (HR) Id4905
Bonner DurchmusterungBD+56 1627
Henry Draper Designation112185

Visual Facts

Star Type star
ConstellationUrsa Major
Absolute Magnitude-0.21 / -0.26
Visual / Apparent Magnitude1.76
Naked Eye VisibleYes - Magnitudes
Right Ascension (R.A.)12h 54m 01.63
Declination (Dec.)+55d 57` 35.4
Galactic Latitude61.16 degrees
Galactic Longitude122.18 degrees
1997 Distance from Earth40.30 Parallax (milliarcseconds)
 80.93 Light Years
 24.81 Parsecs
2007 Revised Distance from Earth39.51 Parallax (milliarcseconds)
 82.55 Light Years
 25.31 Parsecs
Galacto-Centric Distance24,158.92 Light Years / 7,407.00 Parsecs
Proper Motion Dec.-8.24 ± 0.15 milliarcseconds/year
Proper Motion RA.111.91 ± 0.20 milliarcseconds/year
B-V Index-0.02
Radial Velocity-12.70 ± 0.20 km/s
Iron Abundance0.00 ± 9.99 Fe/H
Spectral TypeA0p
Brightest in Night Sky33rd
Colour(A) blue

Variable Star Details

Variable Star ClassRotating
Variable Star TypeAlpha2 Canum Venaticorum
Mean Variability Period in Days5.076
Variable Magnitude Range (Brighter - Dimmer)1.747 - 1.759

Estimated Facts

Calculated Effective Temperature10,827 Kelvin

Sources and Links

SIMBAD SourceLink

Related Stars

Multi-Star System

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. IdB.D. IdStar CodeMagnitudeR.A.Dec.SpectrumColourYear
112185+56 1627.0A1.80000112.00000-6.00000A0White

Location of Alioth in Ursa Major

Alioth (Epsilon Ursae Majoris) Location in Ursa Major

The map was generated using Night Vision, an awesome free application by Brian Simpson.

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