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ALPHA RET (Alpha Reticuli). Though shining at relatively prominentthird magnitude (3.35), and the luminary of the modernconstellationReticulum (the Net), AlphaReticuli is largely ignored by the research community since thegreat majority of astronomers are in the northern hemisphere wherethey cannot see it, the star easily visible only from south of theTropic of Cancer. If in the northern hemisphere, Alpha Ret wouldbe a common star within most statistical data bases (and probablywould have had an "ancient" proper name). Lying at a distance of163 light years, Alpha Ret is a yellow class G (G8) "brightgiant," that is, is somewhat onthe bright side even for a giant star. Radiating at a luminosityof 237 Suns from its coolish 4940 Kelvin surface, the star has agiant's radius 21 times that of theSun, andhas a rotation period slow enough that it has never been measured(with an upper limit of 130 days). It does, however, radiate X-rays, which shows magnetic activity likely induced by rotation. Alpha Ret's temperature and luminosity together with the theory ofstellar structure suggest a mass 3.5 times that of the Sun. Arather standard "clump giant" (a star that quietly fuses its heliuminto carbon and oxygen), only 300 million years ago it was aluminous blue class B star. Upon burning up the rest of itsinternal helium, it will undergo a great brightening phase and thenpop its external envelope as it prepares to become awhite dwarf. Unless it istorn away by the gravity of passing stars, all this action willcontinue to be witnessed by a small twelfth magnitude class M0dwarf companion. Over the past 150 years, the little one has keptthe same motion as the big one, showing that the two really aremated and not just a line of sight coincidence. (Technically, theyare a called a "common proper motion" pair, "proper motion" beingthe movement of the star against the distant background.) Theseparation of 49 seconds of arc translates into a minimum physicalseparation of 2450 Astronomical Units and an orbital period of atleast 60,000 years. At this distance, from Alpha Ret proper thecompanion would glow 4 or so times our Venus at maximum, while fromthe companion, Alpha Ret would shine with the light of 15 fullMoons.
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