Universe Guide

Alioth (Epsilon Ursae Majoris, 77 Ursae Majoris) Star Facts

Alioth Facts

  • Alioth is a rotating variable star that can be located in the constellation of Ursa Major. The description is based on the spectral class.
  • Alioth is a main star of the constellation outline.
  • Based on the spectral type (A0p) of the star, the star's colour is blue - white .
  • Alioth is the 32nd 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.
  • Alioth has a radius that is 4.14 times bigger than the Suns. Radius
  • Using the most recent figures given by the 2007 Hipparcos data, the star is 82.55 light years away from us. Distance

Alioth's Alternative Names

Epsilon Ursae Majoris (Eps Uma) is the Bayer Classification for the star. The Bayer Classification was created by Johann Bayer in 1603. The brightest star in the constellation is normally given the Alpha designation, there are exceptions such as Pollux which is Beta Geminorum.

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.

Flamsteed designations are named after the creator, Sir John Flamsteed. Sir John named the stars in the constellation with a number and its latin name, this star's Flamsteed designation is 77 Ursae Majoris. The Flamsteed name can be shortened to 77 Uma.

BD number is the number that the star was filed under in the Durchmusterung or Bonner Durchmusterung, a star catalogue that was put together by the Bonn Observatory between 1859 to 1903. The star's BD Number is BD+56 1627.

More details on objects' alternative names can be found at Star Names .

Location of Alioth

The location of the variable star in the night sky 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 object is compared to the celestial equator and is expressed in degrees. For Alioth, the location is 12h 54m 01.63 and +55° 57` 35.4 .

Radial Velocity and Proper Motion of Alioth

Proper Motion

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 milliarcseconds/year towards the north and 111.91 ± 0.20 milliarcseconds/year east if we saw them in the horizon.

Radial Velocity

The Radial Velocity, that is the speed at which the star is moving away/towards the Sun is -12.70000 km/s with an error of about 0.20 km/s . When the value is negative then the star and the Sun are getting closer to one another, likewise, a positive number means that two stars are moving away. Its nothing to fear as the stars are so far apart, they won't collide in our life-time, if ever.

Physical Properties of Alioth

Alioth Temperature and Colour

Based on the star's spectral type of A0p , Alioth's colour and type is blue - white variable star. The star's effective temperature is 9,020 Kelvin which is hotter than our own Sun's effective Temperature which is 5,777 Kelvin.

Alioth Luminosity

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 136.57 that I have given is based on the value in the Simbad Hipparcos Extended Catalogue at the University of Strasbourg from 2012.

Alioth Radius

Alioth Radius has been calculated as being 4.14 times bigger than the Sun. The Sun's radius is 695,800km, therefore the star's radius is an estimated 2,880,612.00.km. If you need the diameter of the star, you just need to multiple the radius by 2.

Alioth Mass

The Alioth's solar mass is 2.91 times that of our star, the Sun. The Sun's Mass is 1,989,100,000,000,000,000,000 billion kg. which to calculate using this website is too large. To give idea of size, the Sun is 99.86% the mass of the solar system.

Alioth Iron Abundance

Alioth 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. The value comes from the Hipparcos Extended Catalog.

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 40.30000 which gave the calculated distance to Alioth as 80.93 light years away from Earth or 24.81 parsecs. If you want that in miles, it is about 475,757,151,451,749.56, based on 1 Ly = 5,878,625,373,183.61 miles.

In 2007, Hipparcos data was revised with a new parallax of 39.51000 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.

Using the 2007 distance, the star is roughly 5,220,525.87 Astronomical Units from the Earth/Sun give or take a few. An Astronomical Unit is the distance between Earth and the Sun. The number of A.U. is the number of times that the star is from the Earth compared to the Sun. 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*.

Travel Time to Alioth

The time it will take to travel to this star is dependent on how fast you are going. U.G. has done some calculations as to how long it will take going at differing speeds. A note about the calculations, when I'm talking about years, I'm talking non-leap years only (365 days).

The New Horizons space probe is the fastest probe that we've sent into space at the time of writing. Its primary mission was to visit Pluto which at the time of launch (2006), Pluto was still a planet.

DescriptionSpeed (m.p.h.)Time (years)
Airbus A38073675,216,579.79
Speed of Sound (Mach 1)767.26972,151,230.83
Concorde (Mach 2)1,534.5436,075,568.39
New Horizons Probe33,0001,677,557.66
Speed of Light670,616,629.0082.55

Variable Type of Alioth

The star is a rotating Alpha2 Canum Venatic 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.

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Additional Alioth Facts and Figures

Visual Facts

Primary / Proper / Traditional NameAlioth
Alternative NamesEpsilon Ursae Majoris, Eps Uma, Al-Jawn, HD 112185, HIP 62956, HR 4905, 77 Ursae Majoris, 77 Uma, BD+56 1627, eps UMa
Spectral TypeA0p
Constellation's Main StarYes
Multiple Star SystemYes
Star TypeVariable Star
GalaxyMilky Way
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.)+55° 57` 35.4
Galactic Latitude61.16462958 degrees
Galactic Longitude122.18059961 degrees
1997 Distance from Earth40.30000 Parallax (milliarcseconds)
 80.93 Light Years
 24.81 Parsecs
2007 Distance from Earth39.51000 Parallax (milliarcseconds)
 82.55 Light Years
 25.31 Parsecs
 5,220,525.87 Astronomical Units
Galacto-Centric Distance24,158.92 Light Years / 7,407.00 Parsecs
Proper Motion Dec.-8.24000 ± 0.15000 milliarcseconds/year
Proper Motion RA.111.91000 ± 0.20000 milliarcseconds/year
B-V Index-0.02
Radial Velocity-12.70000 ± 0.20 km/s
Iron Abundance0.0000 ± 9.99 Fe/H
Semi-Major Axis8805.0000000
Stellar Luminosity (Lsun)136.5700000
Brightest in Night Sky32nd

Companions (Multi-Star and Exoplanets) Facts

Exoplanet CountNone/Unaware

Variable Star Details

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

Estimated Calculated Facts

Radius (x the Sun)4.14
Effective Temperature10,827 Kelvin
Mass Compared to the Sun2.91

Sources and Links

SIMBAD SourceLink

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 Location in Ursa Major

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

Ursa Major Main Stars

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