NU CET (Nu Ceti). The roundish head of Cetus, the Sea Monster, is led in brightness by Menkar, which at third magnitude (2.53) is the Alpha star in spite of it being a distinct second to second magnitude (2.04) Beta Ceti (Deneb Kaitos). But by its very name, "Deneb" (from Arabic for "tail") is housed at rear of the beast, while fainter Menkar is at the front, clearly showing that Bayer also had position in mind while Greek-lettering the stars. Way down in drawing Cetus's Head is fifth magnitude (4.70) Lambda Ceti, while barely beating it to the bottom is our fifth magnitude (4.86) Nu Cet. Though faint to the eye, it's actually a fairly impressive class G (G8) giant 340 light years away (give or take just 8). That and the equally secure temperature of 5040 Kelvin (from which we find a small amount of infrared radiation) leads to a luminosity 128 times that of the Sun and a radius 15 times solar. Because they rotate so slowly, rotation speeds (as derived from the broadening of spectrum lines) of giant stars are often unmeasured. Here, though, we see a projected equatorial spin rate of 3.7 kilometers per second, which gives a ponderous rotation period that could be as long as 204 days. Theory tells of a fairly massive star, one of three or so Suns, that started off life nearly 400 million years ago as a warm class B8 dwarf, and is now either fusing helium in its core or will do so shortly. Nu Ceti will then eventually lose its outer envelope and expire as a white dwarf of roughly 0.7 solar mass (all stars dying with much less mass than they started with, their ejecta becoming fodder for new stars). Among the better features of Nu Ceti is a faint companion 8.4 seconds of arc away. Writing from the nineteenth century, Smythe and Chambers tell us of "A double star in the Whale's eye...A 4 1/2, pale yellow; B 10, blue. This very delicate object (is) marked difficult...." Modern observations of Nu Ceti B make it a ninth magnitude (9.1) class F (F7) star, the apparent blue color of Nu-B caused by contrast effects. Over the past 180 years, the two have tracked each other well against the distant background, so Nu Ceti B most almost certainly belongs to Nu proper. Magnitude, distance, and an adopted temperature of 6300 Kelvin give a luminosity that is double solar, a mass of 1.25 Suns, and an age consistent with that of "A." From its angular separation, "B" must be at least 875 Astronomical Units away from "A" (the foreshortening not known), and assuming the above masses, takes more than 11,000 years to make a full circuit. From the orbiting companion, the grand giant would appear to the naked eye as a brilliant yellow-orange point of light dozens of times brighter than the full Moon.

Written by Jim Kaler 12/21/12. Return to STARS.