To the reader:
The Skywatcher's Diary for February 2003 has been prepared by
David Batch. Credit to the author and to
Abrams Planetarium,
Department of Physics and Astronomy at
Michigan State University, and mention of
our
Sky Calendar, would be
appreciated.
A sample issue of the Sky Calendar is available over the Internet. It
can be viewed via the World-Wide Web at
http://www.pa.msu.edu/abrams/SkyCalendar/Index.html
If you would like a printed sample of the February issue, please send a long,
self-addressed stamped envelope to:
February Sky Calendar
Abrams Planetarium
Michigan State University
East Lansing, MI 48824
Each month, the Department of Physics and Astronomy at Michigan State
University makes the Skywatcher's Diary available over the Internet. It can
be accessed at
http://www.pa.msu.edu/abrams/SkyWatchersDiary/Diary.html
Current and back-issues of the Skywatcher's Diary are available in our
archives
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ftp://www.pa.msu.edu/pub/swd/
Skywatcher's Diary: February 2003
New Moon occurs at 5:48 a.m. EST or 18:48 in the time zone for China. The reason the latter is significant is that this new moon marks the beginning of the Chinese New Year. The traditional Chinese calendar is luni-solar, that is, based on movements of the sun and Moon. The start of the year is determined by the second new moon that follows the winter solstice, as reckoned from China. Welcome to the year 4700, the year of the Sheep.
Look for the young Moon tonight shortly after sunset. The thin, fragile arc of moon will sit 5 degrees (about 10 moon diameters) above the west-southwest horizon 45 minutes after sundown. It's a wonderful sight. You may initially need binoculars to help pull the image out of the twilight glow. Jupiter reaches opposition (to the sun) this morning, so it rises at sunset and sets at sunrise. In other words, the giant planet is visible all night long. It is also closest to Earth for the year. That distinction is particularly significant to telescope observers. Jupiter now appears about 50% larger than when farthest from Earth.
The exquisite crescent Moon is easy to spot tonight as long as you look within an hour and a half after sunset. The Moon perches 13 degrees (a fist) above the west-southwestern horizon an hour after sundown and sets about one and a half hours later. Tomorrow night the Moon is nearly twice as high and closer to southwest at the same time. It sets an hour later than tonight.
Mercury, the most elusive of the naked-eye planets, now appears in the morning sky, rising about 1 1/2 hours before the sun. An hour before sunrise it sits only 3 degrees up between east-southeast and southeast. The planet shines at magnitude zero but may not be obvious because of its low altitude and the glow of dawn. Mercury just "rounded the bend" in its orbit (greatest elongation) and is heading back toward the sun, so if you want to see it, be sure to look in the next several days.
Some morning soon compare Mars to Antares. The planet and star can be found in the east-southeast about 20 degrees (2 fists) up an hour before sunrise. Mars and Antares are close to the same magnitude, near 1.0. The bodies are separated by 6 degrees, with Mars sitting to the upper left. Look closely at the objects' colors. Most people, with patience, can detect a slight red or orange hue to the planet. Antares has nearly the same color, as it turns out. In fact, its name means "rival of Mars," referring to this coincidence.
Four planets now inhabit the dawn. An hour before sunrise Mercury peeks 2 degrees above the east-southeast horizon. Bold Venus is 15 degrees up in the southeast and 20 degrees (2 fists) to the upper right of Mercury. Look for fainter Mars another 20 degrees to the upper right of Venus. The three planets are nearly aligned with the brightest one centered. The fourth planet is also brilliant but sits on the other side of the sky, low in the west-northwest. Can you guess its identity? In the paragraph describing events several days ago, it was portrayed as visible all night. That's it, Jupiter, king of planets.
The Moon, between 5 and 6 days old, makes a fine subject for binocular viewing tonight. The lower half of the terminator (left side of the Moon) appears quite rough. Several individual craters may be visible, depending on the clarity of the night, the quality of your binoculars, and how steady you can hold them. Look for the three prominent ones near the center of the terminator. The most conspicuous is Theophilus, a crater 65 miles in diameter and about 5 miles deep. In a telescope it reveals a large central mountain peak.
The winter stars, the most brilliant of the year, are spread across a large portion of the southeastern sky and stretch almost from horizon to overhead. Catch Sirius some night in twilight when this brightest of stars is low in the southeast. Look carefully for the flashes of color emitted by this beauty. The prismatic effect results when the beam of light from Sirius headed toward your eye is bent, or refracted, into the rainbow colors. The sensation is enhanced through binoculars.
The Moon passed Last Quarter phase at 6:11 a.m. EST. Careful observers tonight will be able to tell that the Moon is slightly more than half illuminated. Luna approaches the collection of bright winter stars sometimes known as Orion and Friends. It will remain in the vicinity of the group for the next 5 nights. This evening the Pleiades star cluster sits 6 degrees (12 moon diameters or half a fist) above and slightly left of Luna while the bright star Aldebaran appears 14 degrees to the left and a little below it.
The Moon perches about 5 degrees above Aldebaran, the brightest star in Taurus, the Bull. Several fainter stars in the vicinity, plus Aldebaran, form a V-shaped group usually associated with the bull's head. Most of those faint stars belong to another star cluster known as the Hyades, whose members appear much more widely spaced than the Pleiades. In fact, a number of fainter stars, lying as far as 20 degrees away from the V shape, are part of the cluster. All of these stars are attached to one another by gravity and share a common motion through space.
A treat tonight: the gibbous Moon passes near Saturn. Minimum separation, about 2 degrees (4 moon diameters), occurs this evening but even by the time the pair sets tomorrow morning, the distance between them only increases by 1 degree. Today the Equation of Time reaches 14 minutes, its maximum for the year. That number expresses the difference between Apparent Solar Time (time told by a sundial) and Mean Solar Time (clock time).
Mercury is getting more difficult to see. Look for it some morning soon. Tomorrow morning the planet sits only 2 degrees above the horizon 45 minutes before sunrise, so you'll need an unobstructed horizon. It's between southeast and east-southeast and 20 degrees (2 fists) to the lower left of brilliant Venus. Even though Mercury is currently zero magnitude, the same as Saturn in the evening sky, you may need binoculars to assist in locating it. The thicker haze and brighter twilight glow near the horizon could make Mercury a challenge.
Tonight the Moon hangs near the two bright stars that mark the heads of the Gemini twins. This evening the pair sits 7 degrees (less than a fist) to the left of the Moon. Pollux is the lower and more luminous of the siblings. Castor perches 4 degrees above his brother. If you catch them before moonset tomorrow morning, say 2 hours before sunrise, you will notice the orientation of the three objects has changed. The Twins then sit above the Moon and only 4 degrees separate Pollux and Luna.
The Moon slips between the Gemini Twins and Jupiter tonight, but clearly closer (about 3 degrees) to Pollux than the planet. Tomorrow night watch for the Moon to appear 5 degrees (half a fist) to the left of Jupiter. The following night (Sunday) Luna skips to the vicinity of Regulus, heart of Leo. It then sits 4 degrees to the upper left of that star.
If you've ever watched the Full Moon rise, you probably witnessed the famous "moon illusion." The Moon typically appears significantly larger when it's near the horizon than after it has climbed high in the sky. "Appears" is the important word here, since the Moon's size does not change; only our estimation of it does. The illusion is so strong you might not be convinced it's your mind playing tricks. Measure the Moon's size for yourself. Take an empty paper towel tube and sight the Moon through it at rising and again when the Moon's high. The Moon takes up the same space in the tube both times. The next several nights provide a good time to test the effect.
The Moon reaches Full phase tonight at 6:51 p.m. EST, about the same time it rises in the prairie states. In colonial America the full Moon of February was known as the Snow Moon. Many of the Native American tribes also had names for full moons that were linked to circumstances in nature. The eastern Algonquin Indians, for example, called this the Hunger Moon. The Osage, a semi nomadic tribe of Missouri and Arkansas knew it as the Light of Day Returns Moon.
What's the brightest star in Orion? Betelgeuse is probably the best known of the mighty hunter's stars, but Rigel is brighter. This blue supergiant marks one of Orion's feet. Its blue-white color contrasts well with the red supergiant Betelgeuse. Rigel's color comes from its sizzling 20,000-degree-Fahrenheit surface temperature, about twice as hot as our yellow sun. The star's name derives from Arabic "rijl" meaning "foot."
Betelgeuse, the shoulder of Orion, is a dying star, which probably accounts for its irregular brightness. The variable star's magnitude ranges from about +0.2 to +1.2 over a span of hundreds to thousands of days. Try your hand at determining its brightness by using comparison stars Aldebaran (+0.87) and Procyon (+0.41). Check your results against the American Association of Variable Star Observers' database at www.aavso.org/vstar/vsotm/1200.stm.
Now that the Moon rises several hours after sunset, we are in the two-week period of moonless evenings, the time to observe faint objects. This is also the time of year when the zodiacal light is best seen in evening. The zodiacal light is a faint wedge of light visible at the end of astronomical twilight, currently about 1 1/2 hours after sunset for mid northern latitudes. It follows the zodiac (hence the name) because its source is sunlight reflecting off of dust particles in the plane of the solar system. Look for the dim pyramid shape in the west and west-southwest.
Like the zodiacal light, the Gegenschein is another faint shimmering of sunlight reflected off of interplanetary dust. The soft oval glow appears exactly opposite the sun in the sky (gegenschein means "counter glow" in German), so you need to observe near the middle of the night when the glow, currently near Leo, is highest. The sky must be exceedingly clear and dark. The Gegenschein is so faint many experienced observers have never seen it.
Saturn is approaching the point in its orbit where it momentarily appears stationary to us. The Ringed Planet has been retrograding (moving westward) against the background stars, an effect created when we pass Saturn in its orbit. The relative motions of the two planets make it seem to us that Saturn is traveling backwards for a time. Now it resumes its normal eastward trek until retrograding again in late October.
Tomorrow morning the Moon enters the boundary of Scorpius. It appears among the stars of the scorpion's head. Antares, the heart of the arachnid, hangs 9 degrees (a fist) to the Moon's lower left. The star Delta in Scorpius (also known as Dschubba) sits closer, only 1 1/2 degrees (3 moon diameters) to the lower left of Luna. Normally magnitude 2.3, Dschubba has unexpectedly brightened in the last several years. It now shines at almost 1st magnitude. Look for it before dawn.
Tomorrow morning the Moon perches almost between Mars, on the left, and the planet's rival Antares, on the right. The colors and luminosities of Mars and the star are similar, although Mars will soon outshine Antares. The next morning (Tuesday) the Moon slips 5 degrees below Mars and to the left. It has also crossed the boundary into Sagittarius, the Archer, commonly nicknamed the "Teapot" for the shape of its major stars. The Moon sits above the "spout," buoyed up by the steam rising out of the teapot, perhaps.
Cassiopeia, the Queen, is one of the basic constellations, a pattern you should learn if you are not familiar with it. The queen sits on her throne, about halfway up in the northwest toward the end of dusk. Although some people try to imagine a queen, the usual shape that comes to mind is a lopsided "W." Three 2nd-magnitude and two 3rd-magnitude stars comprise the form. The W is standing on its broader end these evenings, with the open part of the figure facing right, toward north. The W is about a fist width long, from top to bottom.
Tomorrow morning before sunrise the Moon sits among the stars of the teapot's handle, part of Sagittarius. The brightest star of the handle, Nunki, or Sigma, is only half a degree (1 moon diameter) above the Moon. Venus gleams 14 degrees (more than a fist) to the left and slightly lower. The next morning (Thursday) you can spot the last easy-to-find crescent Moon before it reaches New phase 6 degrees below and slightly right of Venus.
A great celestial joke plays out beneath the feet of Orion each evening. There lies a smattering of faint stars (the brightest is 3rd magnitude) that make up the constellation of Lepus, the Hare. The quarry of the mighty hunter is right there in plain sight, and next to his formidable great dog, Canis Major, but neither dog nor master seem to notice. Their attention is focused on Taurus, the Bull.
If you would like a star map that can help you identify these and other interesting objects in the current sky, send a stamped, self-addressed envelope to Sky Calendar, Abrams Planetarium, Michigan State University, East Lansing, MI 48824.
A thin crescent Moon awaits early risers tomorrow, but you'll need to be alert to spot it. Although still 2 1/2 days away from New phase, the Moon sits quite low in dawn glow. Look 30 minutes before sunrise between southeast and east-southeast. The Moon appears 2 degrees above the horizon, so you'll need a flat landscape. Binoculars will help if you initially have trouble locating the crescent. Timing is important. Fifteen minutes earlier and the Moon will just be rising. Fifteen minutes later and sunlight dominates.
Most mid northerners don't suspect what beauty lurks only a few degrees below their southern horizon, 2 hours after sunset. Canopus, the second brightest nighttime star, hides there, never quite able to climb into view. Observers below a line running across the U.S. approximately from Nashville to Las Vegas do see the dazzler for a brief time, low in the south. For every degree of latitude you travel farther south, the star climbs a degree higher in the sky. The star belongs to the constellation of Carina, the Keel, originally part of Argo, the ship used in the quest for the Golden Fleece.
Please send any comments, suggestions, or questions to
Thomas G. Ferguson:
fergus52@msu.edu
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