Looking straight up at 9:00 p.m. on February 15.
North is at the
top of the chart. Image generated by Cartes du Ciel, Version 3.0.
Save our skies
Be a considerate neighbor:
Reduce nighttime glare.
Shield all your outside
(or turn them off completely)
and enjoy the beautiful,
starry night sky.
TWINS OF TWINS OF TWINS
This month, we will return to the Zodiac and explore one of its
members—the Twins. Gemini is above and to the northeast of
Orion, and is easily visible in the winter nighttime sky. February
is a great time to brave the cold and admire this grouping of stars.
This constellation lies right along the Milky Way and the ecliptic,
the region in which the Sun and planets roam.
The heads of the Twins are the bright stars Pollux, which is yellowish,
and Castor, white and a bit dimmer than Pollux. Pollux is the sixteenth-brightest
star in the sky; Castor is the twentieth-brightest. But if you take
a closer look at Castor, it is actually a grouping of six stars
all bound to one another by gravity, forming one of the most remarkable
examples of a multiple-star system in the heavens. Even at fifty
light-years away, a modest telescope will show a pair of similar
stars only a couple seconds of arc apart. The brighter, Castor A,
is mid-second magnitude (1.9), the fainter, Castor B, mid-third
(2.9). About an arc minute away to the south lies a third companion,
Castor C, at a faint ninth magnitude. The bright pair are in elliptical
orbit about each other with a four-hundred-year period, and are
now about as close in the sky as they can get. The dim companion
is relatively far away from the bright pair, about one thousand
times the distance between the Earth and the Sun.
With a larger telescope and spectrographic equipment, astronomers
have found that the two bright components, Castor A and Castor B,
are both double stars. Castor A’s stars are almost identical
to each other. Both are about two solar masses, and circle each
other every 9.2 days. That makes them about a tenth of Mercury's
distance from the Sun apart. Castor B's twin stars are real speed
demons, making their circuit around each other in a mere 2.9 days.
And, as a last hurrah for Castor, the faint distant member, Castor
C, is also double. It, too, consists of two much cooler low-mass
dwarfs. These two are only about two sun diameters apart and orbit
each other every twenty hours. It seems ironic that one of the Gemini
Twins is itself three sets of twins, or should I say sextuple.
Pollux is the sixteenth-brightest star in the sky and is about
thirty-four light-years away from Earth. This star is a typical
red giant that is quietly fusing helium into carbon and oxygen in
its deep core. Perhaps Pollux's greatest claim to fame is an orbiting
planet. This is unusual because it is one of the very few red giants
with a planet, and it is the brightest star with a planet. The planet’s
mass is at least 2.9 times that of Jupiter and orbits in near-circular
orbit at a average distance of 1.69 astronomical units in a 1.6-year
orbit. That would place it just outside of Mars’s orbit if
the planet were in our solar system. From the planet, Pollux would
seem to be 5.7 times bigger than the Sun in our sky.
One other interesting object located in Gemini is its Zeta star.
Zeta Gemini is the most distant star in the constellation, about
twelve hundred light-years from Earth. It is a Cepheid variable
star that pulsates, expanding and contracting with a regular period.
Every ten days, Zeta’s brightness changes between its dimmest
magnitude, of 4.2, to its brightest magnitude, of 3.6.
According to mythology, the Twins were the sons of Zeus and Leda
and brothers of Helen, whose face launched a thousand ships and
caused the Trojan War. Ancient mariners regarded Pollux and Castor
as the patrons of seafarers, and in Elizabethan times they were
also considered the protectors of all at sea. In astrology, Gemini
is the third sign of the Zodiac and is associated with storytellers,
communicators, and youth.
The middle of January held a surprise visit by Comet McNaught. It
turned the corner around the Sun on January 15 inside the orbit
of Mercury. The heating from the Sun made the comet burst to life
and become visible in the evening sky if you had a clear view of
the horizon. Even now, if you were extremely careful, you could
use binoculars to see the comet in daylight—that is a bright
comet! Warning: never look directly at the Sun with your naked eyes
and especially not with binoculars. Unfortunately, as the comet
rounds the sun, it will be great viewing for the Southern Hemisphere.
All we New Mexicans can do is look at the pictures. A great gallery
of pictures can be found at www.spaceweather.com.
THE PLANETS AND THE MOON
• Mercury may just peak above the eastern horizon before sunrise
the last week of the month.
• Venus will be easy to locate in the west after sunset; it
will be the brightest thing in the sky.
• You will need to be an early riser to see Mars late this
month. It will rise just ahead of the Sun starting around February
21, but you will need a clear view of the horizon.
• Look for Jupiter to rise after midnight in the east. The
Moon will rise with Jupiter about 3:00 a.m. on February 12.
• Saturn rises about 8:00 p.m., with the Moon just above it
on February 2. On March 1, you can find the Moon and Saturn almost
overlapping about 9:00 p.m.
• The Moon is full on February 2 and new on February 17.
If you have a question or comment for Charlie,
you may e-mail him, at