Gamma Leonis — ししの二重星

Gamma Leonis B (Gamma-2 Leo) is the fainter half of the famous Algieba double star system in Leo. The pair consists of two K-type giants about 130 light-years away — a K1 primary and a G7 secondary — in a 554-year orbit. Gamma-2 contributes magnitude 3.80 to the combined system magnitude of 1.98. The pair's separation is currently about 4.6 arcseconds and widening slowly.

Gamma Leonis is one of the showpiece double stars of the northern sky. Split the pair with any 3-inch telescope at 100x — both components appear as matching yellow-orange giants. The secondary is about a magnitude fainter than the primary, and the color match makes the scene look like twin suns. Find Algieba on the Lion's mane, partway between Regulus and Adhafera. Best observed February through May.

The Algieba name (an Arabic word for "forehead" or "mane") traditionally applies to the combined system; modern catalogs distinguish Gamma-1 (the brighter star, named Algieba by the IAU) from Gamma-2. The binary nature was noted by William Herschel in 1782, and the orbit was first computed in the late 19th century.