When is the best time to observe Alkaphrah?

Alkaphrah is best observed from January through March, with peak visibility during February when it transits around midnight in the Northern Hemisphere.

Where is Alkaphrah located in the sky?

Alkaphrah lies in the constellation おおぐま at right ascension 09h 04m and declination +47° 09′.

What telescope do I need to split Alkaphrah?

Splitting Alkaphrah requires an aperture of roughly 200 mm or larger — the components are separated by about 0.3″ at magnitudes near 3.6. Larger apertures and steady seeing help resolve the pair cleanly.

Alkaphrah — おおぐまの二重星

HIP 44471; Kappa Ursae Majoris; 12 Ursae Majoris

等級 3.6^m DoubleStar おおぐま (UMa) 可視

星図 + リスト + 計画

Alkaphrahについて

説明

Alkaphrah, Kappa Ursae Majoris, is an A1 III giant about 360 light-years away, forming the southern half of the First Leap of the Gazelle with Talitha (Iota UMa). Alkaphrah is itself a close binary, with two nearly equal components about 0.05 arcseconds apart and an orbital period of roughly 36 years — too close for visual resolution in amateur scopes. Combined magnitude is 3.60.

観測のコツ

Alkaphrah and Talitha lie about 0.7 degrees apart west of the main Big Dipper, forming one of the sky's most graceful bright pairs. In binoculars they show distinct colors: Alkaphrah is pure white-blue, Talitha slightly yellower. The close binary within Alkaphrah is a spectroscopic target; visual observers see only one point of light. Circumpolar from mid-northern latitudes.

歴史

The name Alkaphrah comes from the Arabic "al-qafrah" (the springing), referring to the leap of the gazelle fleeing the bear's paws in pre-Islamic astronomy. The spectroscopic binary nature was identified through radial-velocity measurements in the early 20th century.

豆知識

Despite its Bayer designation of Kappa (the tenth letter), Alkaphrah is one of the brighter stars on the outskirts of Ursa Major and serves as a handy signpost for locating the more distant faint galaxies of Leo and Lynx that lie just to the south.