Tau Ceti (taw, t'ow see -tÿ, set -ee) (τ Cet) An orange-red main-sequence dwarf star in the constellation Cetus and one of the Sun's near neighbors. It is located in the sky just northeast of Diphda (β Ceti). Tau Ceti is comparable in size and mass with the Sun but is only about three-fifths as luminous. Dust has been detected around it but there is no hard evidence that Tau Ceti has a planetary or even a stellar companion. It appears, however, to be an optical double, with a 13th-magnitude red dwarf of spectral class M lying 90′ away from it. mv : 3.5; Mv : 5.8; spectral type: G8 Vp; distance: 3.65 pc.