The brightest star on the left-hand side of each picture is Mirfak, Alpha Persei, while the brightest on the right-hand side is Algol, Beta Per. In the reference picture at left, Algol is in its uneclipsed state and nearly as bright at Mirfak. In picture at right, taken the night of October 9, 2004, Algol is in mid-eclipse, and notably dimmed. Compare with other stars in the field as well. The star immediately to the right of Algol, Rho Persei is also variable. Copyright J. B. Kaler.