GAMMA MIC (Gamma Microscopii). Little Microscopium, the constellation of the Microscope, is one of the most obscure figures of the sky. Lying due south of Capricornus and due west of Piscis Austrinus, its brightest star, Gamma Microscopii (no proper name), is only fifth magnitude (though at 4.67, bright fifth). Alpha is just a bit fainter, though the difference hard to detect. While seemingly ordinary, the star and the constellation have a pair of stories well worth the telling. Gamma Mic is a modest class G (G6) giant with a temperature of 5100 Kelvin, a luminosity 64 times that of the Sun, and a radius just 10 times solar. Its physical conditions fall right between the two stars of the binary that make Capella of Auriga. It is a good representative of the "clump" stars that huddle together at about the same surface temperatures and luminosities and that are quietly fusing their internal helium into carbon and oxygen. Our Gamma comes in at about 2.5 solar masses, and only 620 million years ago began its life as a class B9 dwarf. A faint 14th magnitude companion lies 26 seconds of arc away. Observation suggests that the two are not moving through space together, but are merely a line-of-sight coincidence. If they are indeed a pair, Gamma Mic B is a dim red dwarf at least 1800 Astronomical Units away from its big brother and takes at least 43,000 years to orbit. In the first of the stories, the star tells of the chaotic history of the constellations. Microscopium was invented after John Flamsteed mapped the sky in the latter part of the 1600s, His stars are numbered east to west within their constellations. Greek-lettered stars also carry such Flamsteed numbers. Bright Fomalhaut, the luminary of Pisces Austrinus (and its Alpha star), is also 24 Piscis Austrini (24 PsA). The boundaries of Microscopium later cut into Piscis Austrinus, leaving Gamma Mic also as 1 PsA! 2 PsA and 4 PsA are in the "wrong" constellation as well. Several other examples of this kind of mismatch dot the sky. To begin the second story, though not noticeable to the naked eye, stars move, all of them orbiting the center of our Galaxy. Gamma Mic is now moving away from us at 15 kilometers per second. Plotting the stellar path backwards, astronomers found that 3.8 million years ago, the star made a close pass to the Sun, when it was only 6 light years away and by far the brightest star in our sky, shining at magnitude -3 and rivalling Venus. Sirius, our brightest star now, will someday lose its place to yet another.
Written by Jim Kaler. Return to STARS.