Eta Ceti is a star in the equatorial constellation of Cetus. It has the traditional name Deneb Algenubi or Algenudi; Eta Ceti is its Bayer designation, which is Latinized from ÷ Ceti and abbreviated Eta Cet or ÷ Cet. The apparent visual magnitude of this star is +3.4, making it the fourth-brightest star in this otherwise relatively faint constellation and visible to the naked eye. The distance to this star can be measured directly using the parallax technique, yielding a value of . It is drifting further from the Sun with a line of sight velocity component of +12 km/s.
This is a giant star that has been chosen a standard for the stellar classification of K2âÂÂIIIb. It has exhausted the hydrogen at its core and evolved away from the main sequence of stars like the Sun. (The classification is sometimes listed as K1.5 IIICN1Fe0.5, indicating a strong CN star with higher-than-normal abundance of cyanogen and iron relative to other stars of its class.) It is probably on the red giant branch fusing hydrogen in a shell, although there is a possibility that it is a red clump star that is generating energy through the nuclear fusion of helium at its core.
Eta Ceti has 1.7 times more mass than the Sun and its surface has expanded to 13 times the Sun's radius. It is radiating 74 times as much luminosity as the Sun from its photosphere at an effective temperature of 4,356 K. This heat gives the star the orange-hued glow of a K-type star.
The name Deneb Algenubi was from Arabic ðÃÂè çÃÂÃÂÃÂ÷ó çÃÂìÃÂÃÂèàâ al-dhanab al-qayá¹Âas al-janà «bë, meaning the southern tail of the sea monster. In the catalogue of stars in the Calendarium of Al Achsasi al Mouakket, this star was designated Aoul al Naamat (ãÃÂàçÃÂÃÂùçàçê â awwil al naýÃÂmÃÂt), which was translated into Latin as Prima Struthionum, meaning the first ostrich. This star, along with ø Cet (Thanih al Naamat), àCet (Thalath Al Naamat), ö Cet (Baten Kaitos) and àCet, were Al NaýÃÂmÃÂt (çÃÂÃÂùçàçê), the Hen Ostriches.
In Chinese, (), meaning Square Celestial Granary, refers to an asterism consisting of ÷ Ceti, ù Ceti, ø Ceti, ö Ceti, àCeti and 57 Ceti. Consequently, the Chinese name for ÷ Ceti itself is (, ).
In 2014, two exoplanets around the star were discovered using the radial velocity method. Planets discovered by radial velocity have poorly known masses because if the orbit of the planets were inclined away from the line of sight, a much larger mass would have to compensate for the angle in order to generate the measured signal.
Eta Ceti b has a minimum mass of and an orbital period of 403.5 days (about 1.1 years), while Eta Ceti c has a minimum mass of and an orbital period of 751.9 days (2.06 years). Assuming the orbits of the two are coplanar, then the two planets must be locked in a 2:1 orbital resonance, otherwise the system would become dynamically unstable. Although the inclinations from the line of sight are unknown, the value is constrained to be 70ð or less: if any higher, the higher masses would render the system dynamically unstable, with no stable solutions.