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Algol, Beta Persei, 26 Persei, HD19356, HIP14576, HR936

Algol (Beta Persei) is a blue eclipsing main sequence dwarf star that can be located in the constellation of Perseus. Algol is the 61st 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.

Beta Persei is the Bayer Classification for the star. 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.

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.

Location of Algol

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

Proper Motion of Algol

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 miliarcseconds/year towards the north and 2.99 ± 1.40 miliarcseconds/year east if we saw them in the horizon.

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 73.0000000 that I have given is based on the Spectral Types page that I have found on the Internet. You might find a different figure, one that may have been calculated rather than generalised that I have done. The figure is always the amount times the luminosity of the Sun. It is an imprecise figure because of a number of factors including but not limited to whether the star is a variable star and distance.

Physical Properties (Colour, Temperature, Radius) of Algol

Algol has a spectral type of B8V. This means the star is a blue main sequence dwarf star. The star is 7424.00000000 Parsecs from the Galactic Centre or terms of Light Years is 24214.3666585600000000s. The star has a B-V Colour Index of 0 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 9,531 Kelvin.

Algol 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. However with the 2007 release of updated Hipparcos files, the radius is now calculated at being round 3.60. The figure is derived at by using the formula from SDSS and 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 35.14 which gave the calculated distance to Algol as 92.82 light years away from Earth or 28.46 parsecs. It would take a spaceship travelling at the speed of light, 92.82 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 36.27 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.

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*.

Variable Type of Algol

The star is a eclipsing Beta Persei (Algol)/Semi-Detached System (subtype) 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.

Algol Facts

Alternative Names

Traditional/Proper NameAlgol
Flamsteed Name26 Persei
Flamsteed Short Name26 Per
Short Namebet Per
Arabic NameAl-Ghul
English MeaningThe ghoul
Bayer DesignationBeta Persei
Hipparcos Library I.D.14576
Yale Bright Star Catalogue (HR) Id936
Bonner DurchmusterungBD+40 673
Henry Draper Designation19356

Visual Facts

Star Typemain sequence dwarf star
Absolute Magnitude-0.18 / -0.11
Visual / Apparent Magnitude2.09
Naked Eye VisibleYes - Magnitudes
Right Ascension (R.A.)03h 08m 10.13
Declination (Dec.)+40d 57` 20.3
Galactic Latitude-14.90 degrees
Galactic Longitude148.98 degrees
1997 Distance from Earth35.14 Parallax (milliarcseconds)
 92.82 Light Years
 28.46 Parsecs
2007 Revised Distance from Earth36.27 Parallax (milliarcseconds)
 89.93 Light Years
 27.57 Parsecs
Galacto-Centric Distance24,214.37 Light Years / 7,424.00 Parsecs
Proper Motion Dec.-1.66 ± 0.86 milliarcseconds/year
Proper Motion RA.2.99 ± 1.40 milliarcseconds/year
B-V Index0.00
Radial Velocity3.70 ± 3.90 km/s
Semi-Major Axis19.00
Orbital Period (Days)680.05
Argument Of Periastron130.29
Spectral TypeB8V
Brightest in Night Sky61st
Colour(B) blue

Variable Star Details

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

Estimated Facts

Luminosity (x the Sun)73.0000000
Calculated Effective Temperature9,531 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
19356+40 673.0A4.000002.00000B8Blue/White

Location of Algol in Perseus

Algol (Beta Persei) Location in Perseus

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

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