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MENKALINAN (Beta Aurigae). Beautifully shapedAuriga, the Charioteer, rides high innorthern winter skies, dominated by brilliantCapella at the northwestern corner ofthe prominent pentagon that makes the figure. Almost immediately tothe east lies a mid-second magnitude star, Menkalinan (Men-KAL-in-an), at the northeast corner, the Arabic name meaning"the shoulder of the rein-holder." Though the third brightest starin the classic pentagon, Menkalinan carries Auriga's "Beta"designation. The second brightest,Elnath, close to firstmagnitude, connects Auriga with Taurus, and though it has theformal name Gamma Aurigae, is more properly known as Beta Tauri,technically leaving Menkalinan second brightest in Auriga. AsPolaris locates theNorth Celestial Pole andMintaka inOrion's Belt the celestialequator, Menkalinan locates the "solstitial colure," the greatcircle in the sky that passes through both celestial poles and thesummer andwinter solstices. Immediately south liesTheta Aurigae,while to the north is equally closeDelta Aur (who tells the full story).A line passed through these three stars to the north points to the North Celestial Pole, while to the south it points atBetelgeuse inOrion, the summer solstice (the location of the Sun on the firstday of summer) lying inGeminiabout half way between Theta and Betelgeuse. (Pi Aurigae, just north of Menkalinan, adds nicely to the line as well.) Menkalinan is a classA star with a temperature of 9200 Kelvin, not very much differentfromVega orSirius. From its distance of 82 lightyears, we calculate a luminosity 95 times that of theSun, somewhatbrighter than a normal "A star" should be. Careful observationreveals that every 3.96 days, the "star" undergoes a partialeclipse of about a tenth of a magnitude, showing that it actuallyconsists of TWO almost identical stars in a tight orbit, each about48 times more luminous than the Sun separated only about one-fifththe distance between the Sun and Mercury. They may both be"subgiants" that have begun to change and brighten as a result ofexhaustion of their core hydrogen fuel. They are so close thatthey distort each other through mutual tides, neither of themround. A faint red dwarf far below naked-eye vision appears toorbit the pair at least 330 Earth-Sun distances away, from whichthe bright pair would be just barely separable by eye.
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