(Aired on the SWAOG Astronomy Net on 2/13/03)
Gemini is located just up and to the left of Orion during the
early evening hours of February and March. Gemini is one of the
constellations of the zodiac. Our Sun transits through Gemini
starting at the end of June through the end of July.
The two principle stars of Gemini are Castor and Pollux, two of
the most recognizable stars in the heavens. Castor is the alpha
star and is made up of two blue-white spectroscopic double-stars
and a red dwarf double, so Castor is actually a total of six
stars, two of which can be seen by small telescopes! Pollux, the
beta star, is a magnitude 1.1 yellow giant, 10 times the size of
our Sun, and is actually brighter than Castor, even though
Castor, at magnitude 1.6, is listed as the alpha star. The
methods used for measuring magnitude in the early days were not
as accurate as today’s methods, so sometimes the brightest
star of a constellation may not necessarily be the alpha star.
Castor is about 45 light-years away, and Pollux is 35 light-years
from us.
The best way to remember which one is which is to remember that
Castor faces the star Capella (2-Cs), and Pollux faces the star
Procyon (2-Ps).
Pollux is one of seven 1st magnitude stars that make up the
“Winter Circle” of stars. The others are Capella,
Aldebaran, Rigel, Sirius, Procyon, and in the center of the
Circle, Betelguese.
The constellation represents the twins Castor and Pollux. The
Twins are really only half-brothers. They share the same mother
Leda, but have different fathers. Castor's father, and
Leda’s husband, was Tyndareus, the king of Sparta. The
father of Pollux was none other than Zeus. Zeus visited Leda on
her wedding night disguised as a swan. Castor was mortal and
Pollux was not. When Castor was killed in battle, Pollux asked if
he could share his immortality with his brother. His wish was
granted and they were placed in the sky together. Pollux had a
sister, the beautiful Helen of Troy, who would become Queen of
Sparta, and whose abduction lead to the Trojan War.
The twins were very close to each other. Together they joined the
Argonauts' expedition with Jason and his quest for the Golden
Fleece. Apollonius Rodius, the author of the Argonauts'
story, tells that the twins saved the ship Argus during a storm.
For this reason they became protectors of the sailors, who
believed that they saw them as flames leaping from their masts
during the storms. This phenomenon is known today as St.
Elmo's fire.
The constellation of Gemini contains several interesting deep sky
objects.
M35 is an open cluster at the feet of Castor, near the border
with Taurus. It consists of over 100 stars, scattered in an area
about the same size as the full Moon and is easily seen in small
scopes. M35 is approximately 2800 light-years away from us and is
sometimes known as the Kermit Cluster (by FVAS members).
The next interesting DSO is NGC 2392, a planetary nebula that
appears as an 8th magnitude bluish disk with a 10th magnitude
central star. In large telescopes, this nebula has the shape of a
face surrounded by a fringe or fur collar. For this reason it is
called the Eskimo Nebula or the Clown Face Nebula. It is
estimated to be approximately 10,000 light-years away.
There are several other interesting Deep Sky Objects in Gemini.
The list includes open clusters NGC 2158, NGC 2157, NGC 2129, NGC
2266, NGC 2355, NGC 2395, & NGC 2420 and planetary nebula NGC
2371. Consult your favorite star atlas to locate and view these
objects.
Besides Castor, one of the best doubles in Gemini is Mu, containing a magnitude 2.9 star and a magnitude 9.8 companion. At a separation of 73 arc-seconds, it should be a pretty easy target for smaller scopes.
Epsilon Geminorum contains a 3rd magnitude star with a 9th
magnitude companion. At a separation of 110 arc-seconds, it
should also be an easy target for smaller scopes.
There are also several variable stars in Gemini. Zeta & Eta
are naked-eye variables.
Go out on the next clear night and view some of the wonderful
objects in this constellation, and let us know what you think!
Copyright © 2003 by Jeff Benuzzi