To the reader:
The Skywatcher's Diary for February 2002 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
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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
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Current and back-issues of the Skywatcher's Diary are available in our
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Skywatcher's Diary: February 2002
The three bright outer planets span just less than 90 degrees in the evening sky. Look south an hour after sunset. From left to right, they align brightest to faintest. Jupiter is the dazzling object about halfway up in the east. Saturn is two-thirds of the way up in the southeast, and Mars will be found just under halfway up in the southwest. Both Jupiter and Saturn are in bright zodiac constellations, Gemini and Taurus, respectively, while Mars sits among the faint stars of Pisces.
Groundhog Day has made a media celebrity out of a furry rodent most of us couldn't otherwise recognize. Long before groundhog predictions, the celebration was known in Europe as Candlemas, the time when clergy blessed candles and distributed them to the people. It was the point midway between the winter solstice and vernal equinox, a "cross-quarter" day. Early on it became associated with weather forecasting. From an old Scottish couplet: "If Candlemas Day be bright and clear, There'll be two winters in the year."
Mr. Groundhog may have cornered the market on weather forecasting, but the stars reliably predict the seasons. Regulus, the 1st-magnitude star in Leo, the Lion, rises about an hour after sunset in the east-northeast. To some, the lion heralds spring, so the appearance of Regulus announces that warmer days are on the way. This approach to seasonal forecasting is as reliable as any calendar. The lion sits in the same place on the same date and time, year after year after year. Wait until dark, gaze at Leo, and think spring.
The Moon passes Last Quarter phase this morning at 8:33 a.m. EST. You will find the orb about 25 degrees above the horizon in the southwest at that time. Catch it before dawn and you will see that the Moon perches about halfway between Spica, in Virgo, and Antares, in Scorpius. The faint zodiac constellation between those two, where the Moon currently resides, is Libra, the Scales. Look carefully for a 3rd-magnitude star about 5 moon diameters below Luna. It is Alpha in Libra, known to its friends as Zubenelgenubi, an ancient Arabic name indicating the star was once considered part of the scorpion's claw. Alpha is also a double star.
This morning the waning crescent Moon lies 13 degrees (a fist width) to the upper right of the ruddy 1st-magnitude star, Antares, heart of Scorpius. Tomorrow morning the Moon sits 6 degrees to the upper left of the star. By Thursday morning the Moon slides 15 degrees to the left of, and slightly below, Antares. Although it seems as though the Moon must be among the stars of the scorpion these three mornings, it is instead in Libra this morning and then Ophiuchus, the "13th" constellation of the zodiac.
Mars trudges steadily eastward relative to the background stars. And yet night after night we see it standing in nearly the same place in the southwestern sky. How can this be so? The answer is that the background stars also appear to move, but in the opposite direction. Their apparent motion is that of the Earth. As we orbit the sun, the stars slowly drift toward the west, week after week, month after month. Currently, the two motions - that of Mars and the Earth - nearly cancel each other out from out vantage point, producing an apparently stationary Mars.
Tomorrow morning a slim crescent Moon hovers just above the southeastern horizon an hour before sunup. It sits atop the "Teapot" of Sagittarius, although the stars of that pattern are too dim to easily see, then. Mercury begins a brief morning appearance, too. An hour before sunrise tomorrow, the elusive planet sits almost on the east-southeast horizon, 22 degrees (two fists) to the lower left of the Moon. The following morning (Saturday) the Moon is almost horizontal to Mercury, 11 degrees to the planet's right. That morning is the last opportunity to easily find the thin crescent before New Moon.
Today Mercury becomes stationary, relative to the background stars. It approaches the "turning point" in its orbit (known to astronomers as "greatest elongation") later in the month. The two points don't have to coincide. Remember that Mercury's movement, as seen from Earth, is a combination of the planet's and our motion. The critical adjective is apparent. We observe Mercury's apparent motion. The planet appears to reach a stationary point. Coincidentally, Saturn also reaches its stationary point today.
If tomorrow morning is crystal clear, try to sight the "old" Moon less than 2 days before New. Timing is critical. Twenty-five minutes before sunrise is optimal. At that moment the hairline crescent sits less than a degree above the horizon. Look 9 degrees (a fist width) to the north (left) of due southeast. You will need binoculars to initially detect the Moon in such bright twilight. Mercury can help guide you to the right spot since it hangs 7 degrees directly above the Moon.
Astronomers frequently use Sidereal Time, or "star time," to pinpoint objects of interest in the sky. Unlike clock time, which loosely follows the sun, sidereal time is rigidly aligned with the starry framework. If we know, for example, that the sidereal time is 5 hours, we also know Orion is in the south. Near zero hours sidereal time the Big Dipper is low on the horizon, and so forth. A sidereal clock gains 4 minutes per day on a conventional clock. The two clocks are in sync every year near the autumnal equinox. The U.S. Naval Observatory, at http://tycho.usno.navy.mil/sidereal2.html, provides a web-based sidereal time calculator.
Conventional time historically arose from the motion of the sun across the sky - when the sun was highest, it was "high noon." Sundials were used to keep track of this "apparent solar" time. As society became more complex, the sundial proved too imprecise, so the sundial gave way to the mechanical clock that provided a "mean solar" time based on a fictitious "mean sun." The difference between these two ways of telling time is often referred to as the "Equation of Time." Today the Equation of Time is at a minimum for the year, which means the apparent sun is farthest behind the mean sun, about 14 minutes. For those people living on one of the standard time longitudes, at noon, as indicated by a normal clock, the apparent sun would not yet be due south. It would arrive there 14 minutes later.
The Moon passes New phase at 2:41 a.m. EST. Most people in the U.S. will have to wait until tomorrow night to see the Moon, but those in extreme southern California may catch it tonight with binoculars, and those in Hawaii have a chance at a naked-eye glimpse. The Moon is easiest of all just below the equator - if you'd like to plan a quick tropical vacation. The bright "star" 3 degrees to the right of the Moon is the planet Venus, beginning its return to the evening sky.
Ash Wednesday marks the beginning of Lent, the Christian fast of 40 days. The word "lent" derives from Anglo-Saxon meaning "spring," referring to the season. It is also the basis for the word "long," meant to indicate the lengthening of the days during spring. At 40 degrees north latitude the length of daylight is now increasing by 2 to 3 minutes per day. Over the course of the Lenten period, the days gain almost two hours in length.
Last night was the first time the young Moon was easy to see in the evening sky, setting just before the end of twilight. Tonight the Moon stays up an additional hour. Look for the beautiful crescent in the west-southwest. Use binoculars to carefully examine the Moon over the next several nights. Tonight the largest feature is part of Mare Crisium, Sea of Crisis. It is the smooth, slightly darkened semicircular area just above the center of the crescent.
Tonight the Moon sits 15 1/2 degrees (a fist and a half) below Mars. Tomorrow night the Moon slides closer to the Red Planet. Look for it 6 degrees (12 moon diameters) to the planet's lower left. The following night (Sunday) Luna is 10 degrees to Mars' upper left. Tonight binoculars reveal all of Mare Crisium, the large oval area slightly above the crescent's center. The feature is a huge crater we are seeing greatly foreshortened. It is actually wider than it is tall.
Tonight binoculars reveal Mare Crisium well. The large oval, above center on the crescent, is now clearly darker than the surrounding area. The larger dark area below it is Mare Fecunditatis, Sea of Fertility. Notice its outline is not as regular as Mare Crisium, and it is connected to another sea, Mare Tranquilitatis, only partially visible at its upper left. Mare Tranquilitatis, Sea of Tranquility, should be familiar to anyone who lived through the Apollo missions. It is the place where Neil Armstrong and Buzz Aldrin became the first humans to set down on the lunar surface. The actual landing site is still in darkness tonight.
The second brightest object in the sky tonight - outshone only by the Moon - is Jupiter. An hour after sunset it is two-thirds of the way up in the southeast. The giant planet is currently "retrograding," that is, moving westward relative to the distant stars. Track the planet's motion against the starry background as it scoots toward its "turnaround" point on March 1, and beyond. Every few days note its position compared to the two 3rd-magnitude stars to the west (right) of the planet. They are Mu and Eta in the "feet" of Gemini.
For a star map to help you locate these and other interesting sights, send a self-addressed, stamped envelope to Sky Calendar, Abrams Planetarium, Michigan State University, East Lansing, MI 48824.
The Moon sits almost halfway between Saturn and Mars tonight. It is 21 degrees (2 fists) to the upper left of the Red Planet, and 26 degrees to the lower left of the Ringed Planet. The star Regulus, in Leo, is currently in opposition, which means we (the Earth) are directly between, and in line with, the sun and that star. It also means that Regulus rises at sunset, sets at sunrise, and is above the horizon all night long. And because stars' oppositions, unlike planets', occur on the same date every year, the event can be used as a calendar marker.
The Moon is 13 degrees to the lower right of Saturn this evening. As the Moon orbits the Earth, it travels 13 degrees per day eastward through the zodiac. Therefore, tomorrow night the Moon should be in the vicinity of Saturn. Because the Moon and Saturn's orbits are slightly tilted relative to each other, most of the time the Moon passes above or below the planet. Occasionally Luna's orbit carries it right in front of Saturn and the planet is "occulted." Tomorrow evening is such a time. Don't miss it.
The Moon occults, or covers, Saturn this evening. The event will be visible in darkness for most of the eastern half of North America. Saturn disappears behind the dark edge of the Moon and reappears from the sunlit edge. The event is best viewed with a telescope but binoculars or unaided eye are also worthwhile. Experienced telescopic observers may be interested in attempting to detect the "lost ring." See the article at http://www.lunar-occultations.com/iota/planets2002/0221ring.htm. Specific times for disappearance and reappearance for various cities can be found at http://www.lunar-occultations.com/iota/planets2002/planets2002.htm.
(Lansing: disappearance 7:11 p.m.; reappearance 8:20 p.m.)
The Moon is one day past First Quarter. It splits the two giant planets tonight, 13 degrees (about a fist width) to the upper left of Saturn and 15 degrees to the lower right of Jupiter. Mercury now stands at its greatest angular separation (27 degrees) west of the sun during this morning appearance. Known to astronomers as "greatest elongations," these events generally signal favorable times to locate Mercury. Although Mercury's appearance is relatively poor for northern observers, you should find the planet with a bit of effort. Look 45 minutes before sunrise in the east-southeast. The planet will be low - 3 degrees above the horizon.
The Moon passes within a degree of Jupiter this evening, about 3 hours after sunset. Begin watching early - in twilight. Take a peek every half hour with unaided eye and binoculars to track the Moon's progress. See if you can determine when minimum separation occurs. A telescope is not particularly useful other than to get nice views of Luna and Jupiter and its moons. The Moon does occult (cover) Jupiter from parts of Alaska, northern Canada, western Europe, and Siberia.
Tonight the Moon has slipped 13 degrees (about a fist width) to the lower left of Jupiter. Notice the two bright Gemini Twin stars sitting 6 degrees to Luna's left. Pollux is the lower brother and Castor perches above. If you have the opportunity to view the sky before the start of dawn tomorrow, find the Moon low in the west-northwest. The twins appear slightly closer to the Moon, but now to the upper right, and oriented nearly horizontal.
At the end of evening twilight, notice that the Moon sits between the Gemini Twins, 11 degrees above, and Regulus, in Leo, 25 degrees to the lower left. The zodiac constellation between these two is Cancer, the Crab. Although rather well known, it is one of the faintest constellations. Its brightest star is 4th-magnitude Delta, which sits 5 1/2 degrees (11 moon diameters) below the Moon. Try using binoculars to follow from the Moon to Delta. About two-thirds of the way (4 degrees), and slightly to the left, look for a "swarm of bees" - the Praesepe, or "Beehive" star cluster.
An hour after sunset, the Moon perches 12 degrees overtop Regulus, the star that marks the heart of Leo. A partial circle of fainter stars, to Luna's left, outlines the great beast's head. Tomorrow night the Moon will be found 6 degrees (12 moon diameters) to the left of Regulus. See if you can establish that the Moon is not full tonight. Use binoculars if you have difficulty. Try the same exercise tomorrow night. Full Moon does not occur until Wednesday morning.
You may recall that at the beginning of this month, the three bright planets, Mars, Jupiter, and Saturn were spread 90 degrees across the sky. If so, you will also notice that the angle between Jupiter, high in the south-southeast at the end of twilight, and Mars, in the west-southwest, has shrunk considerably. Those two planets are now separated by 68 degrees. Continue watching every week or so, right into late April when the show gets exciting.
The Moon is Full this morning at 4:17 a.m. EST. In times past it was known at the Snow, Hunger, or Wolf Moon. By coincidence, half a day later the Moon is also closest to Earth for the year - 221,766 miles. Some claim they can detect that the Moon appears larger and brighter at such times, but without instruments to measure the Moon's size or luminance the observation is difficult to make objectively. The real significance of this happenstance comes to those living near a seacoast. They will experience significantly higher than normal tides, a potentially dangerous circumstance if combined with stormy weather.
Venus has been emerging ever so slowly into the evening sky. If you haven't found it yet, look not later than 30 minutes after sunset, near the horizon between west and west-southwest. Binoculars may aid in picking out Venus from its bright twilight surroundings, particularly if you attempt to catch the planet even earlier. Once you've found Venus, try on successive evenings to find it still earlier. How soon can you see it with naked eye? With binoculars?
Please send any comments, suggestions, or questions to
Thomas G. Ferguson:
fergus52@msu.edu
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