The star Alpha Coronae Borealis, also spelt Alphekka and also known as Gemma. It is an eclipsing binary of the Algol type, varying between magnitudes 2.2 and 2.3 with a period of 17.4 days. The two stars are dwarfs of spectral types A0 and G5. Alphecca lies 75 l.y. away.
Subjects: Astronomy and Astrophysics.