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Alfard, Alpha Hydrae, 30 Hydrae

Proper Name(s)Alphard, Alfard
Bayer DesignationAlpha Hydrae
Flamsteed Number30 Hydrae
HR (BSC)3748
Right Ascension9h 27m 35s
Declination-8° 39' 31"
Distance180 light years
55 parsecs
MagnitudeApparent: +2.0
Absolute: -1.7
Spectral ClassK3III orange giant
Optimum VisibilityFebruary / March
NotesAlphard lies somewhat westward of Sirius, and approximately southward of the Sickle in Leo. This is a binary system, in whicb the highly luminous orange giant Alphard A is accompanied by the dwarf Alphard B, probably also of the K-type classification, in an extremely distant orbit that takes nearly a million years to complete.

The brightest of the long string of stars that form the vast but generally rather faint constellation of Hydra, the Water Snake, Alphard forms an approximate equilateral triangle with two more prominent stars to its north: Regulus in Leo and Procyon in Canis Minor. Though only second magnitude, it stands out as the brightest star in its own region of the sky, and this is the reason behind its name: Alphard (often transliterated Alfard) comes from the Arabic for the 'lone' star.

Alphard is notable as being one of the most intrinsically luminous stars known, generating nearly seven hundred times as much energy as the Sun. A giant star of the orange K-type classification, it has a dwarf star, designated Alphard B, in a distant orbit. The outer shell of this immense star (Alphard's diameter is some forty to fifty times greater than the Sun's) shows pulsating patterns that oscillate over periods ranging up to days in length.


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