Interpolation of the orbit of Aa2 around Aa1 with focus on Aa1.Photos taken with the CHARA interferometer in the near-infrared H-band. As our understanding grows (and new types of objects are discovered), the classification criteria change. Algol currently lies at a distance of about 90 light years, but it was once much closer to the solar system. The classification of variable stars has been evolving for more than a century. This is not an artistic representation, but rather is a true two-dimensional image with 1/2 milli-arcsecond resolution in the near-infrared H-band, reconstructed from data of the CHARA interferometer. Algol (β Persei) is a triple-star system (Algol A, B, and C) in the constellation Perseus, in which the large and bright primary Algol A is regularly eclipsed by the dimmer Algol B every 2.87 days. Animation done on Mathematica by Simon Tyran (Yukterez, Vienna, 2.2.2016). Commonly known as the Demon Star, it is one of the best-known variable stars in the sky and a prototype for a class of eclipsing variable stars known as Algol variables. The separation has to be pretty small for the odds to be good this will happen. Tidal distortions of Algol B giving it an elongated appearance are readily apparent. Temperature: 4,500 K, Spectral class:  A7m London. Algol’s eclipses can be observed without a telescope. No. Visible Algol-type variable stars include Mintaka (Delta Orionis, mag. Over time, the more massive and evolved star sheds much of its material, which is accreted by the companion, which then gradually becomes more massive. If we could, we would see that stars vary a great deal in the wavelengths of the light they produce. Constellation: Perseus In 2003, the General Catalogue of Variable Stars listed more than 3,500, which was 9% of all known variables. Today, Algol is the 61st brightest star in the sky at its brightest (mag. Beta Lyrae and W Ursae Majoris variables, is that Algol-type stars have a spherical or slightly ellipsoidal shape. After observing the star to determine the period of its light variations, he suggested that Algol was what we now know as an eclipsing binary, i.e. star if the period, inclination, and radial velocity of each star is known. The star’s Latin name in the 16th century was Caput Larvae, meaning “the Spectre’s Head.”  Medieval astrologers considered Algol one of the unluckiest stars. The form of Algol C, however, is an artifact. Copy this URL to share: Temperature: 13,000 K that it is periodically eclipsed by a dimmer companion of almost the same size as itself. Temperature: 7,500 K. 466. Right ascension: 03h 08m 10.13245s In 2003, the General Catalogue of Variable Stars listed more than 3,500, which was 9% of all known variables. Since you also know the velocity (from Doppler shift) and orbital period, you can get the true scale of the system (including star sizes and masses). The Roche lobe represents the maximum a star can reach before it starts transferring material to the companion. Radius: 1.73 solar radii Other famous deep sky objects in this region include the California Nebula (NGC 1499) and the Heart and Soul nebulae (IC 1805 and IC 1848). The paradox is explained with mass transfer, a phenomenon that is not uncommon in close binary stars. (A milliarcsecond is about the size of a quarter atop the Eiffel Tower as seen from New York City.) Many years ago, many classes of variable were described in terms of a prototype star; and astronomers would define new classes to encompass minor observational differences from known variables. ALGOL: Star b of the constellation of Perseus. Algol’s variability was first correctly explained by the English amateur astronomer John Goodricke in 1782, when he was only 18 years of age. The name Algol comes from the Arabic phrase “raʾs al-ghūl,” meaning the “head of the ghoul” or “head of the demon.”  In Perseus, the star represents the head of the Gorgon Medusa, the mythical monster so horrific in appearance that merely looking at her would turn people to stone. Algol /ˈælɡɒl/, designated Beta Persei (β Persei, abbreviated Beta Per, β Per), known colloquially as the Demon Star, is a bright multiple star in the constellation of Perseus and one of the first non-nova variable stars to be discovered. You will share this with the class as a brief description of the paper and its main points in the discussion forum. The Algol system as it appeared on 12 August 2009. Absolute magnitude: 2.9 Perseus and Caput Medusæ, plate 6 in Urania’s Mirror, a set of celestial cards accompanied by A familiar treatise on astronomy … by Jehoshaphat Aspin. A similar mechanism is at play in other types of eclipsing binary stars. The eclipsing binary pair is separated by only 0.062 astronomical units (AU) from each other, so close in fact that Algol A is slowly consuming the less massive Algol B by continually stripping off Algol B’s outer layers. Absolute magnitude: 2.3 Algol is a triple-star system which dims on a regular basis and when at its brightest it shines three times that as when it’s dimming. The star has been associated with demons, violence and death across different cultures: ghouls in the Arabic world, the Gorgon in Greek mythology, and Rōsh ha Sāṭān (Satan’s Head) in Hebrew folklore. Beta Persei Aa1 and Aa2 form a binary pair. 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