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A Complete Guide to the Solar System and the Night Sky
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public Observing fromLocation: Greenwich, United Kingdom edit_location_alt
north SunriseRise: 7:47  
clear_day Transit: 11:49  
SunsetSet: 15:50 south
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All Constellations » Perseus » 

Algol - β Persei (beta Persei)

Altitude: 7.9°   Azimuth: 27.4°   Direction: North-North-East

Algol, also designated as β Persei (beta Persei), is a variable and multiple main-sequence star in the constellation of Perseus.

Algol visual magnitude is 2.12, making it the 61th brightest star in the sky. Thanks to its high brightness, Algol is clearly visible when observed from locations with dark skyes, and should be also quite easily visible from light polluted areas.

The table below summarizes the key facts about Algol:


Algol - β Persei (beta Persei) is above the horizon from Greenwich, United Kingdom edit_location_alt.

Altitude: 7.9°
Azimuth: 27.4°
Direction: North-North-East

Celestial coordinates and finder chart of Algol

Algol is situated north of the celestial equator, as such, it is more easily visible from the northern hemisphere. Celestial coordinates for the J2000 equinox as well as galactic coordinates of Algol are provided in the following table:

03h 08m 10s
+40° 57’ 20”

The simplified sky map below shows the position of Algol in the sky:

Finder chart Algol - β Persei (beta Persei) star
Simplified finder chart for Algol - β Persei (beta Persei).

Visibility of Algol from your location

Location: Greenwich, United Kingdom edit_location_alt
Latitude: 51° 28’ 47” N
Longitude: 0° 00’ 00” E
Timezone: Europe/London

Algol - β Persei (beta Persei) is circumpolar and transits at 22:10 UTC (altitude: 79.5°)

Digitized Sky Survey image of Algol

The image below is a photograph of Algol from the Digitized Sky Survey 2 (DSS2 - see the credits section) taken in the red channel. The area of sky represented in the image is 0.5x0.5 degrees (30x30 arcmins). The proper motion of Algol is 0.004 arcsec per year in Right Ascension and -0.001 arcsec per year in Declination and the associated displacement for the next 100000 years is represented with the red arrow.

Image of Algol - β Persei (beta Persei) star
DSS2 image of Algol. The red arrow shows the motion of Algol during the next 100000 years (6.67 arcmin in Right Ascension and -1.67 arcmin in declination);

Distance of Algol from the Sun and relative movement

Algol is distant 92.77 light years from the Sun and it is moving far from the Sun at the speed of 4 kilometers per second.

28.46 pc
92.77 ly
4 km/s
0.004 arcsec/year
-0.001 arcsec/year

Spectral properties of Algol

Algol belongs to spectral class B8 and has a luminosity class of V corresponding to a main-sequence star.


The red dot in the diagram below shows where Algol is situated in the Hertzsprung–Russell diagram.

HR Diagram
H-R diagram showing the position of Algol. Attribution: Richard Powell / CC BY-SA

Algol star system properties

Algol is a visual double star which can be observed only with the help of very large telescopes. The table below shows key information about the Algol double sysyem:

81.9 arcsec

Alternative designations of Algol

β Persei
(beta Persei)