Universe Guide

Alcor (80 Ursae Majoris) Star Facts

Alcor Facts

  • Alcor is a main sequence star that can be located in the constellation of Ursa Major. The description is based on the spectral class.
  • Alcor is a main star of the constellation outline.
  • Based on the spectral type (A5V SB) of the star, the star's colour is blue - white .
  • The star can be seen with the naked eye, that is, you don't need a telescope/binoculars to see it.
  • Using the most recent figures given by the 2007 Hipparcos data, the star is 81.72 light years away from us. Distance

Alcor's Alternative Names

The Id of the star in the Yale Bright Star Catalogue is HR5062. HIP65477 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD116842.

Alcor has alternative name(s) :- G Ursae Majoris, G UMa, NSV 06238.

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 80 Ursae Majoris. The Flamsteed name can be shortened to 80 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+55 1603.

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

Location of Alcor

The location of the main sequence 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 Alcor, the location is 13h 25m 13.42 and +54° 59` 16.8 .

Radial Velocity and Proper Motion of Alcor

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 -16.04 ± 0.11 milliarcseconds/year towards the north and 120.21 ± 0.13 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 -9.60000 km/s with an error of about 1.00 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 Alcor

Alcor Colour and Temperature

Based on the star's spectral type of A5V SB , Alcor's colour and type is blue - white main sequence star. The star's effective temperature is 7,955 Kelvin which is hotter than our own Sun's effective Temperature which is 5,777 Kelvin.

Alcor 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 13.29 that I have given is based on the value in the Simbad Hipparcos Extended Catalogue at the University of Strasbourg from 2012.

Alcor Radius

Alcor estimated radius has been calculated as being 1.92 times bigger than the Sun. The Sun's radius is 695,800km, therefore the star's radius is an estimated 1,334,579.13.km. If you need the diameter of the star, you just need to multiple the radius by 2. However with the 2007 release of updated Hipparcos files, the radius is now calculated at being round 1.9269036684565628129943868672. The figure is derived at by using the formula from SDSS rather than peer reviewed papers. It has been known to produce widely incorrect figures.

Alcor Apparent and Absolute Magnitudes

Alcor has an apparent magnitude of 3.99 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 2.01 If you used the 2007 Parallax value, you would get an absolute magnitude of 2.00. 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 Alcor

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 40.19000 which gave the calculated distance to Alcor as 81.16 light years away from Earth or 24.88 parsecs. If you want that in miles, it is about 477,109,235,287,581.79, based on 1 Ly = 5,878,625,373,183.61 miles.

In 2007, Hipparcos data was revised with a new parallax of 39.91000 which put Alcor at a distance of 81.72 light years or 25.06 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 5,168,960.03 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 7,405.00 Parsecs or 24,152.40 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 Alcor

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 A38073674,460,313.75
Speed of Sound (Mach 1)767.26971,425,785.38
Concorde (Mach 2)1,534.5435,712,846.14
New Horizons Probe33,0001,660,690.63
Speed of Light670,616,629.0081.72
Alcor brightness ranges from a magnitude of 4.073 to a magnitude of 4.039 over its variable period. The smaller the magnitude, the brighter the star. Its variable/pulsating period lasts for 0.0 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 Alcor Facts and Figures

Visual Facts

Primary / Proper / Traditional NameAlcor
Alternative NamesG Uma, G Ursae Majoris, G UMa, HD 116842, HIP 65477, HR 5062, 80 Ursae Majoris, 80 Uma, BD+55 1603, NSV 06238
Spectral TypeA5V SB
Constellation's Main StarYes
Multiple Star SystemYes
Star Type Main Sequence Dwarf Star
GalaxyMilky Way
ConstellationUrsa Major
Absolute Magnitude 2.01 / 2.00
Visual / Apparent Magnitude3.99
Naked Eye VisibleYes - Magnitudes
Right Ascension (R.A.)13h 25m 13.42
Declination (Dec.)+54° 59` 16.8
Galactic Latitude61.46862451 degrees
Galactic Longitude112.76946816 degrees
1997 Distance from Earth40.19000 Parallax (milliarcseconds)
 81.16 Light Years
 24.88 Parsecs
2007 Distance from Earth39.91000 Parallax (milliarcseconds)
 81.72 Light Years
 25.06 Parsecs
 5,168,960.03 Astronomical Units
Galacto-Centric Distance 24,152.40 Light Years / 7,405.00 Parsecs
Proper Motion Dec.-16.04000 ± 0.11000 milliarcseconds/year
Proper Motion RA.120.21000 ± 0.13000 milliarcseconds/year
B-V Index0.16
Radial Velocity-9.60000 ± 1.00 km/s
Semi-Major Axis8912.0000000
Stellar Luminosity (Lsun)13.2900000

Companions (Multi-Star and Exoplanets) Facts

Exoplanet CountNone/Unaware

Variable Star Details

Mean Variability Period in Days0.017
Variable Magnitude Range (Brighter - Dimmer)4.039 - 4.073

Estimated Calculated Facts

Radius (x the Sun)1.93
Effective Temperature8,017 Kelvin

Sources and Links

SIMBAD SourceLink

Location of Alcor in Ursa Major

Alcor 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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