Algol (star)
Multiple star Algol (β Persei) |
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Algol in the constellation Perseus | |||||||||||||||||||||||
AladinLite | |||||||||||||||||||||||
Observation dates equinox : J2000.0 , epoch : J2000.0 |
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Constellation | Perseus | ||||||||||||||||||||||
Right ascension | 03 h 08 m 10.13 s | ||||||||||||||||||||||
declination | + 40 ° 57 ′ 20.3 ″ | ||||||||||||||||||||||
Apparent brightness | 2.09 (2.09 to 3.30) mag | ||||||||||||||||||||||
Typing | |||||||||||||||||||||||
B − V color index | −0.05 | ||||||||||||||||||||||
U − B color index | −0.37 | ||||||||||||||||||||||
R − I index | −0.03 | ||||||||||||||||||||||
Spectral class | B8 V | ||||||||||||||||||||||
Variable star type | EA / SD | ||||||||||||||||||||||
Astrometry | |||||||||||||||||||||||
Radial velocity | (3.7 ± 3.9) km / s | ||||||||||||||||||||||
parallax | (36.27 ± 1.40) mas | ||||||||||||||||||||||
distance | (89.9 ± 3.5) ly (27.6 ± 1.1) pc |
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Visual absolute brightness M vis | −0.11 mag | ||||||||||||||||||||||
Proper movement | |||||||||||||||||||||||
Rec. Share: | (2.99 ± 1.42) mas / a | ||||||||||||||||||||||
Dec. portion: | (−1.66 ± 1.22) mas / a | ||||||||||||||||||||||
Physical Properties | |||||||||||||||||||||||
Dimensions | 3.59 0.79 1.67 M ☉ |
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radius | 2.3 3.0 0.9 R ☉ |
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Luminosity |
98 |
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Effective temperature | 12, 000 4500 8500 K |
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Age | <300 x 10 6 a | ||||||||||||||||||||||
Other names and catalog entries |
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Algol ( Arabic الغول al-ġūl 'the demon'), also known as β Persei , is a variable star and the second brightest star in the constellation of Perseus . It is about 90 light years away .
Its apparent brightness changes with a period of 2.87 days (2 days, 20 hours, 48 minutes and 56 seconds) between 2.1 and 3.4 mag, which can also be easily observed with free eyes . In the Arab Middle Ages it was also called the " Devil's Star " because of its inexplicable behavior . It is the prototype of the eclipsing stars .
Algol is a three-star system, consisting of Beta Persei (β Per) Aa1, Aa2 and Ab. The two stars β Per Aa1, a bright bluish star (spectral class B8) with one hundred times the brightness of the Sun , and β Per Aa2, a less bright reddish-yellow star (spectral class K2), orbit each other at a distance of about 0.062 AU . A third star, β Per Ab, with an orbital period of 681 days orbits this binary star system at an average distance of 2.69 AU.
Eclipsing star
In a binary star system, a change in apparent brightness occurs when the less bright star, from the point of view of the earth, passes in front of the brighter star and thereby obscures it. A further smaller fluctuation in brightness occurs between two brightness minima when the brighter star partially covers the weaker star. The Algol stars , a class of eclipsing variables, are named after the characteristics of the light curve of Algol .
The discovery of the changes in brightness are attributed to Geminiano Montanari (1667/1669). The period was determined by John Goodricke in 1783. He suspected it was obscured by a large body or an uneven surface with spots similar to those on the sun. In a letter from John Michell to Henry Cavendish in July 1783, the declaration was mentioned with two different stars. In 1889 Hermann Carl Vogel succeeded in Potsdam in demonstrating from shifts in the Fraunhofer lines in the spectrum of the Algol that it has a dark companion and that both move around a common center of gravity.
However, it can be assumed that the Greek and Arab astronomers had already noticed the change in light that can be seen with the naked eye. New findings indicate that the Egyptians already observed this star and adjusted their day selection calendar to it. Around 1200 BC "Calendar of happy and unhappy days", which originated in ancient Egypt in the 4th century BC, contains regularities that are in harmony with the periodic fluctuations in brightness of the "devil's star" Algol. According to a team of Finnish researchers, the calendar would be the oldest recorded document of the discovery of a variable star. In accordance with astrophysical predictions, the period of Algol 3,200 years ago was slightly shorter than it is today.
Naming
The name Algol is an abbreviation of the original Arabic name»رأس الغول« raʾs al-ġūl 'head of the demon'. It has been used since the 10th century and is one of the oldest Arabic star names in the western world. Ptolemy previously namedthis star Gorgonea Prima ( Latin for "first [star] of the Gorgon") after a Greek legend in which Perseus holdsthe severed head of Medusa (one of the three Gorgons ) in his hands. In astrology, Algol has always been considered a star of disaster.
See also
Web links
- What are double stars? from the alpha-Centauri television series(approx. 15 minutes). First broadcast on Apr 29, 2001.
- http://stars.astro.illinois.edu/sow/Algol.html
Individual evidence
- ↑ a b c Hipparcos catalog (ESA 1997)
- ↑ a b bet Per. In: VSX. AAVSO, accessed November 2, 2018 .
- ↑ a b c Bright Star Catalog
- ↑ Pulkovo radial velocities for 35493 HIP stars
- ↑ a b c Hipparcos, the New Reduction (van Leeuwen, 2007)
- ^ D. Gossman, Light Curves and Their Secrets , Sky & Telescope (October 1989, p.410)
- ↑ Eclipsing Binary simulation , Cornell Astronomy
- ^ The Philosophical Transactions of the Royal Society of London, from Their Commencement in 1665 to the Year 1800. published 1809, p. 456ff (explanation p. 459); Magazine for the latest in physics and natural history. Volume 2, 2nd St., Gotha 1783, pp. 160f ; Astronomical yearbook for the year 1787. Berlin 1784, p. 145
- ↑ Russell McCormmach: Weighing the World: The Reverend John Michell of Thornhill. Verlag Springer Science & Business Media, 2011, p. 360 middle
- ^ Emanuel Müller-Baden: Library of general and practical knowledge, Vol. IV, German publishing house Bong & Co.
- ↑ Porceddu, S., Jetsu, L., Lyytinen, J., Kajatkari, P., Lehtinen, J., Markkanen, T, Toivari-Viitala, J .: Evidence of Periodicity in Ancient Egyptian Calendars of Lucky and Unlucky Days . In: Cambridge Archaeological Journal . 18, No. 3, 2008, pp. 327-339. doi : 10.1017 / S0959774308000395 .
- ↑ Jetsu, L., Porceddu, S., Lyytinen, J., Kajatkari, P., Lehtinen, J., Markkanen, T, Toivari-Viitala, J .: Did the Ancient Egyptians Record the Period of the Eclipsing Binary Algol - The Raging One? . In: The Astrophysical Journal . 773, No. 1, 2013, p. A1 (14pp). bibcode : 2013ApJ ... 773 .... 1J . doi : 10.1088 / 0004-637X / 773/1/1 .