mardi 23 septembre 2008

Equuleus 2

Equuleus, "The Little Horse", is one of the smallest constellations in the heavens. It's quite old, and may have been founded by Ptolemy in the second century AD. However the author of the Almagest often borrowed from others and it is possible his principal source, Hipparchus, was the true creator of this constellation.
The outstanding Greek astronomer Hipparchus (fl 146-127 BC) composed the first star catalogue, of about 850 stars. He also discovered the precession of the equinoxes and invented trigonometry. It is not known if he actually created any constellations.
The "little horse" that the name refers to is lost in antiquity. Some sources believe it to be a half-brother of Pegasus, Celeris. However I've not found any reference to this character. The only brother of Pegasus that I've come across is Chrysaor, born simultaneously with Pegasus. Instead of a horse, Chrysaor was a warrior.
Its original name seems to have been Al Faras al Awwal and the Latin equivalent Equus Primus, "the First Horse", since it rises just before Pegasus.

The asterism is a nondescript triangular form made from the brightest four stars. The brightest of these, alpha Equulei, is called Kitalpha, from Al Kit ah al Faras: "Part of the Horse".
There are only a half dozen Bayer stars, which are generally fifth magnitude.
There are a number of multiple binaries here, but little else.

Double stars:
Gamma Equulei (also known as 5 Equ) is a multiple system with quite faint components (although C is only optical).
AB: 4.7, 11; PA 268º, separation 1.9". C: 12; PA 5º, 47.7". D: 6; PA 153º, 352".
Delta Equulei (also known as Struve 2777) is a multiple system including one of the most rapid visual binaries, with an orbit of only 5.7 years: 5.2, 5.3; 2000 values: PA 33º, 0.2". AC: 9.4, PA 14º, 47.7".
Epsilon Equulei (Struve 2737) is also a multiple system:
AB: 5.2, 6.0; PA 288º, 0.9" C: 7; PA 70º, 10.6". D: 12.5; PA 280º, 74.8".
Lambda Equulei (Struve 2742) is perhaps the most attractive binary in Equuleus. It has two equal but rather faint stars:
7.4, 7.4; PA 218º, separation 2.8".

Variable stars:
None of Equuleus' variables are suitable for amateur viewing; the brightest Mira-type variable (R Equ) only gets to a visual magnitude of 8.7 every 261 days.

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