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.