Minima of Algol

Description

Algol, designated Beta Persei (β Persei), is also known as the 'Demon Star' or 'Gorgona'. It is a triple star system some 90 light-years away in the constellation of Perseus visually shining in beautiful blueish and orange. The young English observer, John Goodricke (1764 - 1786) discovered Algol's steady variability between 1782 and 1783 and speculated that the cause of Algol's regular dimming are eclipses by a 'dark body', perhaps a planet. He also discovered the variation of δCephei and further stars.

Algol Aa1 (or A) and Algol Aa2 (or B) form an eclipsing binary 0.062AU (15% the distance Mercury to Sun) apart with a period of 2.87 days, while the third star, Algol Ab (or C), shines in white at an average distance of 2.69 AU from the pair orbiting with a period of 680.2 days or 1.86 years. The star system is visible with the naked eye at a maximum magnitude of 2.12 lowering to 3.39 during a central eclipse by Aa2. The event occurs every 2.867328 days (the orbital period of β Per Aa1 an β Per Aa2), lasting about 9 hours and 40 minutes, minimum light for about 20 minutes. The Algol system shines brightest (2.12) when no star obstructs another.

 

A primary eclipse occurs when the larger, but cooler and dimmer Algol Aa2 (or B) partially hides the smaller, hotter, brighter and more massive main sequence star Algol Aa1 (or A). A secondary eclipse occurs when Algol Aa1 (A) eclipses Algol Aa2 (B), but this event can only be detected photoelectrically.

The Algol system is strong source of x-ray and radio wave flares as a result of mass transfer and magnetic fields (10x solar), respectively.

About 7.3 million years ago, Algol passed within 9.8 light-years of our Sun at an apparent magnitude of −2.5, outshining today's Sirius. Currently, the system is moving away at a radial velocity of 3.7 km per second. If placed at a distance of 10 parsecs (32.6ly) the absolute magnitude of the primary star would be −0.07, comparable with Arcturus (-0.04) in Boötes.

 

Location on a star chart.

 

DSS-IR image, 1.5° wide (click for a telescope view).

 

 

Physical Comparison

 MassRadiusLuminosityTemperatureSpectral
Algol (A) Aa13.172.7318213,000°KB8
Algol (B) Aa20.703.486.924,500°KK0
Algol (C) Ab1.761.73107,500°KA7
Units in solar unless otherwise specified.

 

Light Curve

 

Prediction of Minima

A selection of 'easy' binaries (visually bright, short period, high Δmagnitude)

* elements not yet confirmed
Select a Variable Star: Date (mm/dd/yyyy):
Universal Times
Local Times UTC +

Star Information

Calculator based on Sky & Telescope, February 24, 2004

 

 


NameTypeEpochPeriod [d]RA (2000)DE (2000)Dist [ly]VmaxVmin
Algol (Beta Persei)eclipsing binary (prototype star Algol)2445641.5542.86732403 08 10.13+40 57 20.3932.123.39
Beta Lyraeeclipsing binary (Algol-type)2455435.112.9376318 50 04.79+33 21 45.69623.254.36
Chi² Hydraeeclipsing binary (Algol-type)2448501.99512.267711 05 57.55-27 17 16.16905.645.92
Delta Cepheipulsating variable prototype star δ Cep2436075.4455.36634122 29 10.25+58 24 54.78873.484.37
Delta Libraeeclipsing binary (Algol-type)2434456.54262.3273490615 00 58.39-08 31 08.22944.915.4
Eta Aquilaepulsating variable (δ Cephei type)2436084.65637.17664119 52 28.36+01 00 20.414003.484.39
i(44) Boötis W Ursae Majoris variable2455352.463440.267818515 03 49.06+47 38 18.1425.86.4
Lambda Taurieclipsing binary (Algol-type)2455178.0813.952947804 00 40.82+12 29 25.34833.373.91
R Araeeclipsing binary (Algol-type)2455347.15594.42513516 39 44.73-56 59 39.94006.177.32
R Canis Majoriseclipsing binary (Algol-type)2445391.2341.1359507 19 28.08-16 23 41.71445.76.34
RR Lynciseclipsing binary (Algol-type)2433153.86239.94507906 26 25.84+56 17 06.42705.526.03
RZ Cassiopeiaeeclipsing binary (Algol-type)2439025.30251.195249902 48 55.51+69 38 03.12046.187.72
Sigma Aquilaeeclipsing binary (Algol-type)2422486.79751.9502719 39 11.64+05 23 52.02045.145.32
U Cepheieclipsing binary (Algol-type)2444541.60312.493047501 02 18.34+81 52 32.18266.759.24
U Sagittae eclipsing binary (Algol-type)2440774.46383.38062619 18 48.41+19 36 37.710136.459.28
V1010 Ophiuchuseclipsing binary (Algol-type)2455758.35470.6614316 49 27.67-15 40 04.712406.17
VZ Cassiopeiaeeclipsing binary (Algol-type)2451565.4054.46722400 45 39.11+74 59 17.33405.786.12
W Sagittariipulsating variable (δ Cephei type)2437678.5787.59418 05 01.22-29 34 48.313354.295.14
Zeta Geminorumpulsating variable (δ Cephei type)2436791.92210.1508207 04 06.54+20 34 13.111833.624.18
μ Herculiseclipsing binary (Algol-type)2448852.36792.05102717 17 19.57+33 06 00.4274.695.37
μ¹ Scorpiieclipsing binary (Algol-type)2449534.1781.4462716 51 52.23-38 02 50.62942.893.15

 

 

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Comments

Claus Agerskov
[24] 2023-11-05 16:43:25
Great infopage about Algol. I just miss the information of the eclipse duration which is 9.6 hours (14%) which will say that the dimming will start 4.8 hours or 4h48m before the minimum. The have the eclipse duration from AAVSO: https://www.aavso.org/vsx/index.php?view=detail.top&oid=26202