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Alphard

Alfard, Alpha Hydrae, 30 Hydrae

Proper Name(s)Alphard, Alfard
Bayer DesignationAlpha Hydrae
Flamsteed Number30 Hydrae
HR (BSC)3748
HD81797
ConstellationHydra
Right Ascension9h 28m 37s
Declination-8° 45' 2"
Distance180 light years
55 parsecs
MagnitudeApparent: +2.0
Absolute: -1.7
Spectral ClassK3III Orange Giant
Optimum VisibilityFebruary / March

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 lies at the heart of a ternary or triple system, with one of its companion stars possibly being a white dwarf. 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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