They're Twins, By Jiminy!
As twilight fades about
7 p.m. on February 1, Capella is low on the horizon. It travels
around from east to north, but does not climb high into the northern
sky. Just rising are twin stars (Castor and Pollux). They seem
to pursue the mighty kangaroo Purra (Capella) as it skirts around
the horizon. The hunters take a shortcut by crossing higher into
the heavens in their chase, but by midnight Purra has hidden below
the northwestern edge of the Earth out of reach. But each year
as the weather changes to the hot, dry climate of the “great
heat” the twin stars overtake, kill, and roast their quarry.
Smoke from the fire—the original Australian “barbie”
perhaps—causes the mirages seen in summers. At least this
is what the aborigines of Queensland say.
In ancient China the twin stars of our modern constellation Gemini
were the twin symbols of the eternal contrasts throughout life,
Yin and Yang. Elements of mystery, Yin is the feminine principle,
water, cold and dark, winter and the Moon; while Yang is masculine,
fire, heat and light, summer and the Sun. They complement each
other, and together they constitute the power of the seasons,
the elements, the world above and the world below, and all of
humanity.
The heroes of Greece and Rome, Castor and Pollux, enter into many
of the myths and fables, including the adventures of the Argonauts
in search of the Golden Fleece. On this voyage a fierce storm
arose, and although the ship was sturdy and all the crew brave
and fearless, still this was a storm such as none had experienced
before. In the midst of the great peril as the fury of the sea
was at its height, Orpheus took up his harp and began to play
the melodies that only he could play to calm the storm. And as
the winds died down and the clouds disappeared, suddenly there
were two stars shining over the heads of the twins Castor and
Pollux. From that time forward, the twins of Gemini have been
the patron gods of sailors and of fishermen.
It was here in Gemini, a zodiacal constellation which lies between
Taurus and Cancer, where both Uranus and Pluto were found. In
1781, William Herschel, then 42 years of age and a church organist,
composer, and music teacher, was a dedicated amateur astronomer
whose habit was to “unbend the mind” from his daily
business by grinding telescope mirrors, or by using the telescopes
he had made to see the heavens and the planets. On March 13, using
one of his telescopes with a mirror 6½ inches in diameter,
he noticed a “curious either nebulous star or perhaps a planet.”
On the next clear night he found it to have changed location and
so reported it to be a comet. Uranus, now to be seen among the
stars of Capricornus, orbits the Sun once in 84 years. It will
return to Gemini for only the third time since it was first seen
about the year 2033. Meanwhile, from its discovery in 1930, Pluto
has progressed only as far as from Gemini to Sagittarius in its
trip around the Sun. It will not return “home” to Gemini
until the year 2177. In mid-January, 1999, Pluto will recross
the orbit of Neptune and again take its place as the most distant
of the planets.
Gemini claims one of the finest open star clusters, M35. This
is a nice object for viewing with binoculars during the evening
hours in February. Another interesting feature of the constellation
is the Eskimo Nebula, a planetary nebula (NGC 2392) with a hot
white dwarf star in its center. In photographs taken with large
telescopes, one can easily imagine the face of an Eskimo peering
out from his seal-fur parka. The illusion comes from a series
of nova explosions that resulted in concentric shells of luminous
material, the outermost being half a light year in diameter.
Aside from their fame as the twin stars of Gemini, Castor and
Pollux are interesting in other ways. Castor, Alpha Geminorum,
is a twin of another sort. A binary star system, it is a pair
of stars, Castor A and Castor B, revolving about their combined
center of mass. And each of these is a spectroscopic binary. In
fact, the entire system is comprised of six stars, including twin
red dwarfs, Castor C (YY Gem), which slowly revolve around both
A and B. Castor shines at magnitude 1.6, but it is outranked by
Pollux at 1.2. Pollux has a diameter of from 12 to 20 times that
of the Sun; it is the closest giant to us, about 35 light years
away.