Alula Borealis — 큰곰의 이중성

Alula Borealis, Nu Ursae Majoris, is a K-type subgiant of spectral class K0 IV about 399 light-years away, marking the northern paw-print of the Third Leap of the Gazelle. It pairs with Alula Australis (Xi UMa) to form the southernmost of the three classic Arabic "leaps" asterisms in Ursa Major. Alula Borealis hosts a known exoplanet, Nu UMa b, a super-Jupiter in a 1600-day orbit.

Alula Borealis and Alula Australis sit 1.5 degrees apart in the south of Ursa Major, and in binoculars they show a distinct orange-yellow hue from Alula Borealis versus Xi UMa's paler yellow. Alula Borealis is easier to identify first: it is the brighter of the two (magnitude 3.49 vs 3.79 for Xi). Best observed January through May.

The name "Alula" comes from the Arabic "al-qafzah al-ūlā," "the first leap," originally applied to the nearer-to-the-bear pair. Over time Western labeling reversed the numbering, so the star farthest from the Dipper became "First" and the nearest became "Third." The discovery of the Nu UMa b planet was announced in 2009.