mercredi 1 octobre 2008

Cassiopeia 7

α, Multiple and slightly variable, 2.2 to 2.8, pale rose.

Schedar is first found in the Alfonsine Tables, and was Schedir with Hevelius; Shadar, Schedar, Shedar, Sheder, Seder, Shedis, Zedaron, etc., elsewhere; and all supposed to be from Al Sadr, the Breast, which the star marks in the figure. Some, however, have asserted that they are from the Persian Shuter for the constellation.
Ulug Beg called it Al Dhāt al Kursiyy from the whole, which Riccioli changed to Dath Elkarti.
Smyth said that it was known as Lucida Cassiopea, — a matter-of‑fact statement, as the brightest star in any sky figure is the lucida.
Birt noticed its variability in 1831, which is now determined as in a period of about 79 days, although irregular.
It culminates on the 18th of November.
Burnham has discovered two additional faint companions, the nearest 17ʺ.5 away; the companion first known, a smalt blue star, having been found by Sir William Herschel, in 1781, 63ʺ away.
α, β, η, and κ were the Chinese Yūh Lang, or Wang Leang.
β, 2.4, white.

Caph, Chaph, or Kaff, on the upper right-hand corner of the chair, are from the Arabic title of the constellation; but Al Tizini designated the star as Al Sanām al Nākah, the Camel's Hump, referring to the contemporaneous Persian figure.
With α Andromedae and γ Pegasi, as the Three Guides, it marks the equinoctial colure, itself exceedingly close to that great circle; and, being located on the same side of the pole as is Polaris, it always affords an approximate indication of the latter's position with respect to that point. This same location, 32° from the pole, and very near to the prime meridian, has rendered it useful for marking sidereal time. When above Polaris and nearest the zenith the astronomical day begins at 0 hours, 0 minutes, and 0 seconds; when due west the sidereal time is 6 hours; when south and nearest the horizon, 12 hours, and when east, 18 hours; this celestial clock-hand thus moving on the heavenly dial contrary to the motion of the hands of our terrestrial clocks, and at but one half the speed.
Beta's parallax, 0ʺ.16, indicates a distance of 20 light years.
Just north of it is an especially bright patch in the Milky Way.
When first Al Aaraf knew her course to be
Headlong thitherward o'er the starry sea.
Edgar Allan Poe's Al Aaraf.
About 5° to the west-northwest of Caph, 1 1/2° distant from κ, and forming a parallelogram with Caph, γ and α, appeared, in 1572, a famous nova visible in full daylight and brighter than Venus at perigee.
Poe's name for it is from the Arabians' Al Orf, — in the plural Al Arāf, — their temporary abode of spirits midway between Heaven and Hell, and so applicable to this temporary star. This object was known for two centuries p147after its appearance as the Stranger, or the Pilgrim, Star, and the Star in the Chayre, but by us as Tycho's Star, although it was first noticed by Schuler at Wittenberg in Prussia, on the 6th of August; again at Augsburg by Hainzel, and at Winterthür, Switzerland, by Lindauer, on the 7th of November; and on the 9th by Cornelius Gemma, who called it the New Venus. Maurolycus began its systematic study at Messina on the 8th, but his published account of it in 1602, in his Astronomiae Instauratae Progymnasmata, has caused his name to be identified with it. Its lustre began to wane in the following December, and it was inserted in the Rudolphine Tables as "Nova anni 1572" of the 6th magnitude, to which it had at that time decreased. It disappeared entirely in March, 1574, so far as could then be known.
This nova is said to have incited Tycho to the compilation of his star-catalogue, as that of seventeen centuries earlier may have been the occasion of the catalogue of Hipparchos. At all events, it created a great commotion in its time, and induced Beza's celebrated prediction of the second coming of Christ, In the same way the comet of 1843 confirmed the Millerites in their belief in the immediate destruction of the world as it was considered a reappearance of the Star of Bethlehem. The statement that this star appeared in 945 and 1264 rests upon the very doubtful authority of the Bohemian astrologer Cyprian Leowitz, and is not credited by our modern astronomers; although Williams asserts that a large comet was seen in the latter year near Cassiopeia. ( According to Humboldt — a source often used by Allen — Leovitius claimed (probably in De coniunctionibus magnis, published in 1564, a few years before Tycho's supernova) to have read in a "manuscript chronicle" that a new star had appeared in those years between Cassiopeia and Cepheus, very near the Milky Way. Leovitius explicitly states that the star was not the same object as the comet ). The reddish 10 1/2‑magnitude, known as B Cassiopeiae, singularly variable in its light, is now to be seen 0ʹ.8 from the spot assigned by Argelander to the star of 1572, and is thought possibly to be identical with it ( Catalogued as SN 1572 (the SuperNova of 1572): modern telescopy finally caught up with it again, or at least with the gas it left behind, since no star seems to have survived. For full historical and technical details, see Hartmut Frommert's page and his further links there).
The Chinese recorded Tycho's nova as Ko Sing, the Guest tar.

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