dimanche 5 octobre 2008

Ursa Major 19

g, or 80 Fl., 4.8.

Alcor is the naked-eye companion of Mizar, and, inconspicuous though it be, has been famous in astronomical folk-lore.
This title, and that of the star ε, Alioth, may be from the same source, for Smyth wrote of it:
They are wrong who pronounce the name to be an Arabian word importing a sharp-sightedness: it is a supposed corruption of al‑jaún, a courser, incorrectly written al‑jat, whence probably the Alioth of the Alfonsine Tables came in, and was assigned to ε Ursae Majoris, the "thill-horse" of Charles's Wain. This little fellow was also familiarly termed Suhā [the Forgotten, Lost, or Neglected One, because noticeable only by a sharp eye], and implored to guard its viewers against scorpions and snakes, and was the theme of a world of wit in the shape of saws:
but Miss Clerke says:
The Arabs in the desert regarded it as a test of penetrating vision; and they were accustomed to oppose "Suhel" to "Suha" (Canopus to Alcor) as occupying respectively the highest and lowest posts in the celestial hierarchy. So that Vidit Alcor, at non lunam plenam, came to be a proverbial description of one keenly alive to trifles, but dull of apprehension for broad facts.
Al Sahja was the rhythmical form of the usual Suhā; and it appears as Al "Khawwar," the Faint One, in an interesting list of Arabic star-names, published in Popular Astronomy for January, 1895, by Professor Robert H. West, of the Syrian Protestant College at Beirut.
Firuzabadi called it Our Riddle, and Al Ṣadāk, the Test, — correctly Ṣaidak, True; while Kazwini said that "people tested their eyesight by this star." Humboldt wrote of it as being seen with difficulty, and Arago similarly alluded to it; but some now consider it brighter than formerly and no longer the difficult object that it was, even in the clear sky of the Desert; or as having increased in angular distance from Mizar.
Although the statement has been made that Alcor was not known to the Greeks, there is an old story that it was the Lost Pleiad Electra, which had wandered here from her companions and became Ἄλώπηξ, the Fox; a Latin title was Eques Stellula, the Little Starry Horseman; Eques, the Cavalier, is from Bayer; while the Horse and his Rider, and, popularly, in England, Jack on the Middle Horse, are well known, Mizar being the horse.
Al Bīrūnī mentioned its importance in the family life of the Arabs on the 18th day of the Syrian month Adar, the March equinox; and a modern story of that same people makes it the infant of the wālidān of the three Banāt.
In North Germany Alkor, as there written, has been der Hinde, the Hind, or Farm Hand; in Lower Germany, Dumke; and in Holstein, Hans Dümken, Hans the Thumbkin, — the legend being that Hans, a wagoner, having given the Saviour a lift when weary, was offered the kingdom of heaven for a reward; but as he said that he would rather drive from east to west through all eternity, his wish was granted, and here he sits on the highest of the horses of his heavenly team. A variant version placed Hans here for neglect in the service of his master Christ; and the Hungarians call the star Göntzol, with a somewhat similar tale. Another Teutonic story was that their giant Orwandil, our Orion, having frozen one of his big toes, the god Thor broke it off and threw it at the middle horse of the Wagon, where it still remains.
In China it was Foo Sing, a Supporting Star.
At the obtuse angle formed with Alcor and Mizar lies the Sidus Ludovicianum, an 8th‑magnitude bluish star, just visible in a field-glass. This was first noted in 1691 by Einmart of Nuremberg, and in 1723 by another German, who, thinking that in it he had discovered a new planet, named it after his sovereign, Ludwig V, landgrave of Hesse-Darmstadt.
1830 Groombridge, or 4010 B. A. C., 6.5,

is the well-known Flying Star, or Runaway Star, that, until Kapteyn's recent discovery of a swifter one in Pictor, had shown the greatest velocity of any in the heavens, although the 7 1/2‑magnitude La Caille 9352 in Piscis Australis, and an 8 1/2‑magnitude in Sculptor, are not far behind it in this respect. According to Miss Clerke,
Argelander discovered in 1842 its pace to be such as would carry it around the entire sphere in 185,000 years, or in 265 over as much of it as the sun's diameter covers.
Another calculator states that in 6000 years it will reach Coma Berenices. This is equivalent to a proper motion of 7ʺ.03 of arc annually, at the rate of over 200 miles a second, and its velocity may be still greater, — a speed uncontrollable, Professor Newcomb says, by the combined attractive power of the entire sidereal universe.
The observations for its parallax do not accord in their results, but Professor Young assigns to the star a distance of 37 1/2 light years.
It is about 16° south from γ, half-way between Coma and stars ν and ξ on the right paw of the Bear; its exact location being 11°46ʹ of right ascension and 38°35ʹ of north declination, about 15° from Ll. 21258, an 8 1/2‑magnitude also much observed for its great proper motion; but 50,000 years hence the Flying Star will have separated from this by at least 100°.
From the foregoing list it will be seen that we have in the entire constellation twenty stars individually named, many of them inconspicuous, two even telescopic, — evidence enough in itself of the antiquity of, as well as the continued popular and scientific interest in, Ursa Major.

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