2 Cor Caroli (Alpha (_) Canum Venaticorum)
A radiant pair with 19.3 arcseconds of separation, Cor Caroli makes for an easy split at lower powers. The brightest point of light in the constellation of Canes Venatici, the Hunting Dogs, Cor Caroli (the name means ‘Charles’s heart’) is easy to spot – it’s the brilliant star 10° south and 10° west of Eta (d) Ursa Majoris, which marks the end of the Plough’s handle.
Both components are spectral type A0 but their colours are not identical. They are mag. +2.8 and mag. +5.5 respectively, so identifying the components is easy. At 62x magnification, the A component appears creamy yellow while the B component comes across as a pale yellow-green. Go to 185x magnification, though, and the B component takes on a pale blue-green tinge.