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Iota Hydrae, 35 Hydrae

Proper NameUkdah
Bayer DesignationIota Hydrae
Flamsteed Number35 Hydrae
HR (BSC)3845
Right Ascension9h 39m 51s
Declination-1° 8' 34"
Distance253 light years
77 parsecs
MagnitudeApparent: +3.90
Absolute: -0.55
Spectral ClassK2.5III orange giant
Optimum VisibilityFebruary / March

An orange star within the northern parts of the long and sinuous constellation of Hydra, Ukdah lies near the celestial equator, and also close to Hydra's border with Sextans, the constellation of the Sextant to the east. At fourth magnitude, it is faintly visible to the naked eye, falling somewhat to the north from Alphard, the brighter Alpha star of Hydra. Ukdah's apparent magnitude is more exactly +3.90, though there are indications that it may vary slightly around this value.

Imagery provided by Aladin sky atlas

Ukdah lies some 263 light years from the Sun, and is an orange giant, having consumed its hydrogen reserves and expanded to a diameter more than thirty times that of the Sun. It has approximately twice the Sun's mass, but generates more than a hundred times as much light. The star has no known companions, and its spectrum is notable for showing unusually high levels of certain metals, notably barium and strontium.

Classically, Ukdah formed part of a hook-shaped group of stars known in Greek as kampē ('the angle' or 'the bend'), and in Arabic as ʽuqdah ('the knot'). This group ran northward from Alphard, and also included 33 Hydrae to the south of Ukdah, and Tau1 and Tau2 Hydrae to the west. The traditional Arabic name for this small star-group was the source of the name Ukdah, which is now formally applied to Iota Hydrae as an individual star.


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