February: February nights are cold, crisp, and clear. Don't miss some of the year's best celestial sights.
Our February chart shows that the Hunter doesn't march alone. He and his celestial friends--Taurus, Auriga, Gemini, Canis Major, and Canis Minor--make a natural grouping simply because they are all attention grabbing. Together they boast eight stars of 1st magnitude or brighter. And if that isn't enough to have you reaching for your coat and hat, consider that Mercury and Saturn are at their best this month too.
A Rare Crescent and a Golden Ring
Two "evening stars" grace our sky this month. The first to appear at the onset of evening twilight is Venus. A veritable beacon glaring at magnitude -3.9, at midmonth Venus stands more than 20[degrees] above the southwest horizon at sunset and sets more than two hours later. Unfortunately, the planet isn't much to look at in a telescope. Its 11-arcsecond-diameter disk is nearly full but featureless. However, Venus will swell in size in the coming months. Watch for the thin crescent Moon floating a few degrees above Venus on the 19th.
Mercury is definitely worth scoping. Although just 7 arcseconds wide when it's most favorably placed this month, the planet's disk is in the shape of a miniature first-quarter Moon. By mid-month, it will be dimming rapidly but will display a striking crescent nearly 10 arcseconds wide--almost the same angular size as Venus. That's because even though Mercury is less than half as big as Venus, on the 15th little Mercury is only half as far from Earth.
Nothing beats Saturn in a telescope. The celebrated rings, which have been closing since 2003, are currently tilted 14[degrees] (with the south face visible) and appear 45 arcseconds wide. A small scope will show the ring system in two parts: the broad, bright B ring and the narrower A ring outside it, separated by the razorthin Cassini Division.
During February, Jupiter and Mars continue to be planetary underachievers in Ophiuchus and Sagittarius, respectively. Jupiter is plenty bright at magnitude -1.9 and rises in the southeast a couple of hours before dawn. Much dimmer Mars (magnitude 1.3) emerges during morning twilight. Look for the crescent Moon 7[degrees] directly below Jupiter at daybreak on the 12th. Two mornings later keep an eye out for an even thinner Moon slipping southwest of Mars in bright twilight.
The East Coast of North America will see the Moon skim the northeast edge of the Pleiades as darkness falls on the 23rd. The Moon is still within 2[degrees] of the cluster by the time the sky darkens on the West Coast.
Sampling the February Deep Sky
That we have so many brilliant stars to admire at this time of year is no accident. Our solar system is located on the inner edge of the Orion Arm of the Milky Way Galaxy. Facing south on a moonless winter's night, rural observers can trace this portion of the Milky Way coursing past Orion and Canis Major to the south horizon. The most dazzling winter stars are galactic neighbors that are bright chiefly because they're close. They're colorful, too. Look up and you'll find that red Aldebaran (in Taurus), yellow Capella (Auriga), orange Pollux (Gemini), white Sirius (Canis Major), and blue Adhara (Epsilon Canis Majoris, below Sirius) are just a few of the winter luminaries whose subtle colors are discernible with binoculars, if not with your bare eyes.
Orion has more. Winter's marquee constellation boasts stars of all colors, sizes, and ages. Betelgeuse, for example, is a cool red supergiant much older than our 5-billion-year-old Sun. Rigel is a hot blue-white supergiant that's been shining for less than 100 million years. Mintaka, the upper-right star in Orion's Belt, is a fantastically hot blue giant that's been around less than 50 million years. Most amazing of all is a tiny cluster called the Trapezium, an easy telescopic target located in the heart of the magnificent Orion Nebula, M42. The Trapezium comprises white-hot stars that may be as little as 10,000 years old! The Orion Nebula itself is a prime example of an emission nebula: a vast cloud of hydrogen gas heated to incandescence by the hot, young stars inside it. When we gaze at this famous nebula we behold a stellar nursery incubating not only new suns but entire solar systems.
M42 is visible to the naked eye as blurry, 4th-magnitude patch in the vertical row of faint stars marking the Hunter's Sword. The nebula should appear in your telescope's finder as a mist enveloping a close pair of 5th-magnitude stars called [Theta.sup.1] and [Theta.sup.2] ([[theta].sup.1] and [[theta].sup.2]) Orionis. A small scope armed with a 50x eyepiece will show that [Theta.sup.1] is the brightest of the quartet of stars forming the 20-arcsecond-wide Trapezium. If the sky is sufficiently dark, the surrounding mist blossoms into an intricate weave of nebulosity about 1[degrees] wide.
Observing with my 4-inch short-focus reflector from my backyard, I can see that the bright core of nebulosity around the Trapezium is a rectangle with two remarkably straight sides. A dark "bay," called the Fish's Mouth, bites deeply into this mottled mist, right up to the Trapezium. A narrow rift of dusty material at the base (just north) of the Fish's Mouth separates M42 from M43, a faint little companion nebula enveloping a 7th-magnitude star. My 10-inch scope shows that M43 is shaped like a fat apostrophe or comma.
Viewed in the 10-inch under a rural sky, the tandem of M42 and M43 is simply mind-boggling. Long threads of nebulosity extend on either side of the Trapezium and transform the Great Nebula into a celestial gull. Its wispy wings curl back, forming a tenuous loop that entangles many dim stars. The bird's round head is marked by M43, and its body is delineated by the rectangular cloud enclosing the Trapezium. The brightest parts in this central region glow greenish gray with tinges of red. Not many deep-sky objects show color, but the Orion Nebula is exceptional in every way.
In contrast to the genesis cloud of M42, a stellar tombstone lies in nearby Taurus. It's the Crab Nebula, M1. The Crab Nebula is a supernova remnant: the shredded remains of an exploded star. Light from that cataclysmic explosion reached the skies of Earth at dawn July 4, 1054. Records from Chinese skywatchers tell us that a brilliant "guest star" appeared in eastern Taurus that morning and remained visible in broad daylight for three weeks. It shone for months before fading from view.
In 1731 English amateur astronomer John Bevis discovered an obscure nebula the same part of Taurus. It was, it turns out, the expanding debris cloud from the same supernova seen seven centuries earlier. French comet hunter Charles Messier chanced upon the object in 1758 and made it the first entry his now-famous catalog of deep-sky objects. The nickname "Crab" surfaced the mid-19th century when Irish astronomer William Parsons made a sketch of the object showing ragged filaments--the luminous shrapnel from the explosion--that vaguely suggested the legs of a crab.
However, the 8th-magnitude Crab isn't in the same league as M42. It's small (about 8 by 4 arcminutes in extent) and presents a pallid face to small scopes. In my 4-inch reflector, M1 is an egg-shaped smudge that barely survives suburban skyglow. My 10-inch does better and shows the oval cloud being narrower and dimmer at one end. When observing M1 in dark skies with the larger scope, I can detect a patchy texture and occasionally hints of the filaments. Alas, the tiny, energetic pulsar (the surviving core of the exploded star) that lies at the heart of the Crab and powers the entire nebula is well beyond the range of amateur instruments.
I wouldn't blame anyone who feels the Crab Nebula is more shadow than showpiece. That said, the payoff with faint nebulae (and bright ones too) is not so much what your eye detects as what your mind's eye perceives. In the case of the Crab, you have in your telescope the ashen aftermath of a violent stellar death witnessed by our ancestors nearly a millennium ago. Definitely worth a trip into the chilly night, I'd say.
The showstopper this month is Saturn. The golden-colored planet comes to opposition (lies 180[degrees] from the Sun's position on the ecliptic) on the 10th, when it rises at sunset and is visible all night. Located just west of the familiar Sickle in Leo, zero-magnitude Saturn is noticeably brighter than Regulus, the 1.4-magnitude star at the Sickle's base. Throughout February, Saturn slowly retrogrades westward toward neighboring Cancer. Watch the planet over a period of weeks and you'll notice its motion as it creeps away from the Sickle.
As February opens, Mercury, the elusive inner planet, is nearly magnitude -1 and slowly gaining altitude above the west-southwest horizon. Mercury reaches greatest elongation (largest angular separation from the Sun) on the 7th, when it hovers about 15[degrees] above the horizon at sunset and sets 1 1/2 hours later. The best time to look is between 30 and 40 minutes after sunset. If you're having trouble locating the planet in bright twilight, try sweeping the horizon with binoculars. Or you can use Venus as a steppingstone--it shines 7[degrees] (about one binocular field) to the upper left of Mercury on the 7th.
Feb 2 Full Moon
Feb 10 Last Quarter
Feb 17 New Moon
Feb 24 First Quarter
FEB 2 The Moon passes 10 arcminutes north of Saturn (as seen from Western Europe).
FEB 3 Observers in Western Canada and Alaska can see the Moon occult Regulus (6:43 PST; the exact time depends on your location) in morning twilight.
FEB 7 Moon at apogee (404,992 km).
FEB 7 Venus and Uranus close together (40' apart at 19h UT).
FEB 7 Mercury at greatest elongation.
FEB 8 Neptune in conjunction with the Sun.
FEB 10 Saturn at opposition.
FEB 19 Moon at perigee (361,436 km).
FEB 23 Moon passes just north of the Pleiades at dusk.
FEB 28 Moon passes 1 1/2[degrees] north of M44, the Beehive cluster.
THE ORION NEBULA
The crimson glow that's dominant in pictures of the Orion Nebula is the spectral hue emitted by energized hydrogen. M42 also contains superheated oxygen atoms that produce a greenish light. At low light levels our eyes aren't very sensitive to color--especially red--so the nebula appears a greenish gray in small telescopes.
BINOCULAR HIGHLIGHT Orion's Sword
Orion's Sword is really three highlights in one. Of course the center of attention is M42 itself. Even under poor conditions, this nebular mist can be seen enshrouding three points of light. These are the Trapezium (its four main stars reduced to a single 4thmagnitude blip by the low magnification of binoculars), 5th-magnitude [[theta].sup.2] ([Theta.sup.2]) Orionis, and its 6th-magnitude neighbor to the east. Together they are an arresting sight worthy of the accolades heaped upon them.
Due south of M42 lies Iota ([iota]) Orionis. At magnitude 2.7 it is the brightest star in the field of view, but look carefully at the star lying 8 arcminutes southwest. Notice anything? This is the double star Struve 747. In my 10 x 50 binoculars I can just split this pair of 4.7- and 5.5-magnitude suns--but only when I use a tripod to steady the view. My 15 x 45 image-stabilized binos have an easy time resolving the double.
The northernmost attraction in Orion's Sword is the loose open cluster NGC 1981. Even under bright suburban skies, steadily held 10 x 50 binoculars show a handful of cluster stars. Although this grouping is often overlooked because of its showier neighbor, it's an attractive cluster worth a look.
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|Date:||Jan 1, 2007|
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