The fourth-largest constellation, straddling the celestial equator. Cetus represents a sea-monster or whale. Its brightest star is Beta Ceti (Diphda). Alpha Ceti is known as Menkar. The most celebrated star in the constellation is the red-giant variable Mira (Omicron Ceti). Tau Ceti, magnitude 3.5, is a star similar to the Sun, lying 11.9 l.y. away. M77, a 9th-magnitude spiral, is the brightest Seyfert galaxy.