ZETA RET (Zeta Reticuli). For observers of the skies south of about 35 degrees south latitude, the modern constellation of Reticulum (the Net) is circumpolar and perpetually visible, its brightest star, Alpha Reticuli, shining at a modest third magnitude. At the extreme western edge of the constellation lies one of the few genuine naked-eye double stars, a two-for-one combination named Zeta Reticuli. Separated by 310 seconds (a bit over five minutes) of arc (0.09 degrees), the sixth magnitude (5.54) western one (Zeta-1) keeps exact pace with the somewhat brighter fifth magnitude (5,24) eastern component (Zeta-2), showing that they are a real gravitational pair (but so far apart that no orbit is detectable). In that sense it is a fine southern hemisphere counterpart to the Big Dipper's Mizar and Alcor and to Epsilon Lyrae. Unlike these, however, it is a quite-remarkable pairing of two SOLAR type stars, Zeta-1 listed as a G3-5 dwarf, Zeta-2 as very-solar G2. (The classification is uncertain, Zeta-1 sometimes given as G2, Zeta-2 as G0). Close to us, the Zeta-pair is only 39.5 light years away. From that and a temperature of 5795 Kelvin, Zeta-2 shines with luminosity almost exactly the solar luminosity, while Zeta-1 (at 5675 Kelvin) comes in at 0.9 Suns, which yield respective radii of 0.9 and 1.0 times solar and subsolar masses of 0.9 and 0.96 solar masses. Given the angular separation and distance, the two are at least 3750 Astronomical Units apart, which with the total system mass of 1.86 solar, gives an orbital period of at least 170,000 years. As if a solar-type double is not enough, what truly sets these stars apart is a bizarre story of an alien abduction in the early 1960s in which one of the abductees spotted a map in the alien spaceship that was later traced back to the home base of Zeta Reticuli! Which of the two stars was not said. Seems unlikely. And it's even more unlikely, since no planets have yet been discovered (though Earth-like ones would be undetectable). Moreover, stars with planets tend to be metal-rich, whereas Zeta Ret is mildly metal deficient, with an iron abundance about 60 percent solar, consistent with a relatively high velocity compared to the Sun (about five times normal). Too bad, as any residents of either Zeta-1 or Zeta-2 could in principle travel back and forth from one star to the other (real star travel being unlikely outside of such pairs). From either, the other would be brilliantly obvious, shining roughly as brightly as 30 times our Venus does in Earthly skies, about the same as a mid-crescent Moon. (Thanks to Jerry Diekmann and Tim De Benedictis who suggested this star.)
Written by Jim Kaler 9/26/08. Return to STARS.