This month we
venture into the realm of the Zodiac, the so-called "birth signs"
of astrology. The constellations of the
Zodiac are bisected by the Ecliptic (on this map the orange line
that runs through Gemini). The Ecliptic is the path that the Sun, Moon,
and planets follow across the sky.
The constellation Gemini has many different origins from different cultures. One such myth derives from ancient Rome. The twins in Gemini are represented by Remus and Romulus, the legendary brothers who built Rome. The bright stars Castor and Pollux are also associated with boxers, and Gemini is sometimes depicted as a pair of sparring partners. (Trivia: In what action movie are two brothers named Castor and Pollux? Click here for the answer.)
To find Gemini in March, go outside between 8 and 9 p.m. local time and face southwest. Find the super-bright, twinkling star Sirius, not very far from the horizon. Then move up and to the right to the unmistakable hourglass shape of Orion. Find the bright orange giant star Betelguese (Orion's left shoulder) and follow his arm up to the feet of Gemini. You'll notice the Twins are standing in the white river of the wispy Winter Milky Way. At locations near 38° N latitude, Gemini stands nearly overhead, and sets feet first in the west as the night wears on.
In this more detailed view, (adapted from Norton's Sky Atlas 2000.0)
we'll take a closer look at some of the
interesting sights in and around Gemini. We're going to go in order
of right ascension, which is right to left on this map. The vertical
lines are the right ascension lines. Also, the symbols at left show how
an object is best viewed:
with your naked eye;
with binoculars,
and
with a telescope.
M 35 and NGC
2168. M35 is one of the grandest of all open clusters. Visible to the
naked eye at a dark sky site, this large cluster explodes into hundreds
of stars with a pair of binoculars or a telescope at low power. A fascinating
deep sky object is the much smaller open cluster NGC 2168, just off the
southwest edge of M 35. At first glance it looks nebulous, like an elongated
galaxy or globular cluster. If you have an 8-inch or larger scope, bump
up the power, and this dense little cluster will begin to show individual
stars.
NGC 2395. This
8th magnitude, medium sized open cluster is interesting because it has
a bar shaped row of stars of identical brightness. In the very center of
this cluster is a lone bright star.
NGC 2392, The
Eskimo Nebula. This bright little planetary has been a target of the
powerful Nordic Optical
Telescope. In amateur telescopes, it appears as a small fuzzy patch
right next to an 8th magnitude star. Larger instruments will show some
detail, including the hooded shape of an "eskimo", which gives the planetary
its name. Use a nebula filter for better contrast.
NGC 2420. This
is a very pretty 8th magnitude open cluster. It's a compact, dense cluster,
surrounded by a diamond of 4 brighter stars. Info
and link to a Picture.
(Note: I observed these double stars on March 1, 1999, between 8:30 and 9 p.m. EST, with an 8-inch f/6 reflector at 88x. The descriptions below are based on these views. Keep in mind a reflector produces an upside down image, and the positions are based on the time at which I observed.)
Castor and
Pollux. The "twin" stars are actually not equal. Pollux is magnitude
1.14, while Castor is 1.98. Remember, in magnitude, like golf, the lower
the number, the brighter the star! Were these two stars equally bright
in ancient times? Castor is actually a multiple star system; 3 stars can
be seen with a good telescope. The two main stars lie only 3.9 arcseconds
apart, while the third star, Castor C, is 70 arcseconds away and shines
at magnitude 9. This is a beautiful trio. Of the two main stars, the lower one
is brighter, while the upper one appears to have a yellowish-orange tint.
Castor C is positioned at 10 o'clock and is much fainter. Pollux is a double star also,
but it cannot be resolved with an optical telescope.
mGem. This double star is a much wider pair, 121 arcseconds apart, and its components shine at magnitudes 3.2 and 9.4. The primary (the brighter star) is yellow-orange in color. The dimmer star (which is very faint!) is itself another double, but only separated by a scant 0.8 arcseconds. (I was not able to resolve it.) It will take a tack sharp optical system to split this pair!
20 Gem. Magnitudes 6.3 and 6.9, separation 20 arcseconds. A nice yellow and blue pair.
l Gem. Magnitudes 3.6 and 10.7, separation 9.6 arcseconds. The primary is whitish, while the secondary appears orange-red and is positioned at 4 o'clock.
d Gem. Magnitudes 3.5 and 8.2, separation 5.8 arcseconds. The primary is yellow-white, and the secondary is at 9 o'clock.
k Gem. Magnitudes 3.6 and 8.1, separation 7.1 arcseconds. The primary has a beautiful lemon-yellow hue, and the secondary is at 7 o'clock.
l, d, and k are
very similar in appearance. Do you see the same colors or other details?
Please send us your observations!
While you're in Gemini's neighborhood, check out these other deep sky treasures:
M44, The Beehive.
Located in nearby Cancer (use the map at the very top to find
its position), the Beehive is impressive using any type of optical
aid, or just your eye. From a dark sky site it's visible as a fuzzy patch
slightly smaller than the full moon, nestled between two stars of 4th and
5th magnitude, respectively. Picture.
NGC 2244, The
Rosette Nebula. Located below Pollux's left foot in the Winter Milky
Way (and labeled on the top map as 2244), the Rosette is a combination
nebula and open cluster. Small telescopes will only show the cluster, while
larger instruments start to bring out hints of nebulosity. Use a nebula
filter. Picture.