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KULLAT NUNU (Eta Piscium). If some star names are more obscurethan others, this one is surely near the bottom of the list. Unlike most star names, which are from Greek, Latin, or especiallyArabic, it seems to have derived from Babylonian and really morerefers to the cord that connect the Fishes ofPisces rather than to the star itself. ThoughAlrescha, the Alpha star, is perhaps bestknown in this dim constellation (as a result of its placement atthe central "kink" in the cord), it is rather well topped byBayer's Eta star, which at bright fourth magnitude (3.69) isPisces' brightest, and somehow deserves a name (so "Kullat Nunu,"while hardly official, will have to do). Best to think of it moreas just plain old Eta Piscium. The star itself is a bit unusual,a bright class G (G7) giant, at 4930 Kelvin a bit cooler thanCapella-A. It is one of the few of itsclass to have had its angular diameter measured. From that and thedistance of 294 light years, Eta is 26 times larger than theSunand would extend 30 percent of the way from the Sun to Mercury. The star's calculated luminosity of 316 Suns and its temperatureconspire to give almost the same answer, showing that the measuredproperties are consistent and correct. In turn, these dataindicate a mass between 3.5 and 4 times that of the Sun and thatthe star is most likely dying and in a state of internal heliumfusion. Only about 250 million years ago it was a hot, blue ClassB star, and in far less time than that, it will turn into a massivewhite dwarf rather likeSirius-B. Spinning with an equatorial velocity of at least 8 kilometers persecond, the giant may take almost half a year to make a full turn. All this activity has been witnessed by a mysterious, relativelydim companion about which nothing is known (and given theuncertainties about it, once might say less than nothing). The"little one" is only a second of arc away from its brightercompanion, making observation difficult. It has been reported tobe as bright as 8th magnitude and as faint as 11th (the result oferror in observation, not of variability). If at 8th, it is ayellow-white class F dwarf, if at 11th, an orange class K dwarf. The companion illustrates a major problem in astronomy, that wecannot see well in three dimensions. If at precisely the samedistance of the bright star, the two are separated by 70 or soastronomical units (1.75 Pluto's distance from the Sun), and wouldhave an orbital period around each other of about 270 years. However, no orbital motion has been seen; that the two are relatedis shown only by the fact that they are moving through spacetogether. Consequently, they must be farther apart, the fainterstar lying somewhat in the foreground or background. There issimply no way to tell.
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