Universe Guide

Algol (Beta Persei, 26 Persei) Star Facts

Algol Facts

  • Algol is a eclipsing main sequence star that can be located in the constellation of Perseus. The description is based on the spectral class.
  • Algol is a main star of the constellation outline.
  • Based on the spectral type (B8V) of the star, the star's colour is blue .
  • Algol is the 60th brightest star in the night sky and the 2nd brightest star in Perseus 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.
  • Using the most recent figures given by the 2007 Hipparcos data, the star is 89.93 light years away from us. Distance

Information on Algol

Algol is one of the brightest stars in the night sky and also in the constellation of Perseus. It gets its name from the Arabic al-ghul meaning (ogre) and is the same inspiration for the enemy of Bruce Wayne - Batman Ra`s Al-ghul (Head of the Ogre). The direct translation of the Arabic name to English is Demon Star. It located where one of Medusa`s eyes would have located if you drew the character Perseus over the star map.

It is one of the first Variable Stars to have been observed. It got its name because the star winked at the observer. In addition to it being a variable star, it is a Multiple Star System, two stars are close together whereas the third is a little way out. The two stars that are close to one another, one eclipses the other which causes the star to appear to wink. The winking is as regular as clockwork, 68 hours, 48 minutes and 59.9 seconds, or 2.86736 days. In the right conditions you can see the wink from start to finish.

ALGOL (ALGOrithmic Language) is also the name of a programming language that was devised in the late fifties then updated in the sixties (60, 68). There is no connection between the star and the programming language as to its name apart from it being the same.

Algol's Alternative Names

Beta Persei (Bet Per) 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 HR936. HIP14576 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD19356.

Algol has alternative name(s) :- , bet Per. In Arabic, it is known as Al-Ghul.

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 26 Persei. The Flamsteed name can be shortened to 26 Per.

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+40 673.

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

Location of Algol

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 Algol, the location is 03h 08m 10.13 and +40° 57` 20.3 .

Radial Velocity and Proper Motion of Algol

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 -1.66 ± 0.86 milliarcseconds/year towards the north and 2.99 ± 1.40 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 3.70000 km/s with an error of about 3.90 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 Algol

Algol Colour and Temperature

Based on the star's spectral type of B8V , Algol's colour and type is blue main sequence star. The star's effective temperature is 9,634 Kelvin which is hotter than our own Sun's effective Temperature which is 5,777 Kelvin.

Algol 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 119.22 that I have given is based on the value in the Simbad Hipparcos Extended Catalogue at the University of Strasbourg from 2012.

Algol Radius

Algol estimated radius has been calculated as being 3.72 times bigger than the Sun. The Sun's radius is 695,800km, therefore the star's radius is an estimated 2,588,884.40.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 3.6026954133978500599926517914. 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.

Algol Apparent and Absolute Magnitudes

Algol has an apparent magnitude of 2.09 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 -0.18 If you used the 2007 Parallax value, you would get an absolute magnitude of -0.11. 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 Algol

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 35.14000 which gave the calculated distance to Algol as 92.82 light years away from Earth or 28.46 parsecs. If you want that in miles, it is about 545,654,007,138,902.68, based on 1 Ly = 5,878,625,373,183.61 miles.

In 2007, Hipparcos data was revised with a new parallax of 36.27000 which put Algol at a distance of 89.93 light years or 27.57 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 5,686,681.08 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 7,424.00 Parsecs or 24,214.37 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 Algol

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 A38073681,940,969.36
Speed of Sound (Mach 1)767.26978,601,577.08
Concorde (Mach 2)1,534.5439,300,737.32
New Horizons Probe33,0001,827,531.92
Speed of Light670,616,629.0089.93

Variable Type of Algol

The star is a eclipsing Beta Persei (Algol)/ 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. Algol brightness ranges from a magnitude of 3.220 to a magnitude of 2.080 over its variable period. The smaller the magnitude, the brighter the star.

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 Algol Facts and Figures

Visual Facts

Primary / Proper / Traditional NameAlgol
Alternative NamesBeta Persei, Bet Per, Al-Ghul, HD 19356, HIP 14576, HR 936, 26 Persei, 26 Per, BD+40 673, bet Per
Spectral TypeB8V
Constellation's Main StarYes
Multiple Star SystemYes
Star Type Main Sequence Dwarf Star
GalaxyMilky Way
Absolute Magnitude -0.18 / -0.11
Visual / Apparent Magnitude2.09
Naked Eye VisibleYes - Magnitudes
Right Ascension (R.A.)03h 08m 10.13
Declination (Dec.)+40° 57` 20.3
Galactic Latitude-14.90026500 degrees
Galactic Longitude148.97650944 degrees
1997 Distance from Earth35.14000 Parallax (milliarcseconds)
 92.82 Light Years
 28.46 Parsecs
2007 Distance from Earth36.27000 Parallax (milliarcseconds)
 89.93 Light Years
 27.57 Parsecs
 5,686,681.08 Astronomical Units
Galacto-Centric Distance24,214.37 Light Years / 7,424.00 Parsecs
Proper Motion Dec.-1.66000 ± 0.86000 milliarcseconds/year
Proper Motion RA.2.99000 ± 1.40000 milliarcseconds/year
B-V Index0
Radial Velocity3.70000 ± 3.90 km/s
Semi-Major Axis8771.0000000
Stellar Luminosity (Lsun)119.2200000
Orbital Period (Days)680.05000
Argument Of Periastron130.29000
Brightest in Night Sky60th

Companions (Multi-Star and Exoplanets) Facts

Exoplanet CountNone/Unaware

Variable Star Details

Variable Star ClassEclipsing
Variable Star TypeBeta Persei (Algol)/
Variable Magnitude Range (Brighter - Dimmer)2.080 - 3.220

Estimated Calculated Facts

Radius (x the Sun)3.60
Effective Temperature9,531 Kelvin

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
19356+40 673.0A4.000002.00000B8Blue/White

Location of Algol in Perseus

Algol Location in Perseus

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

Perseus Main Stars

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