To the reader:
The Skywatcher's Diary for October 2001 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 October issue, please send a long,
self-addressed stamped envelope to:
October 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
at
http://www.pa.msu.edu/abrams/SkyWatchersDiary/Archives.html
ftp://www.pa.msu.edu/pub/swd/
Skywatcher's Diary: October 2001
The Moon rises within a few minutes of sunset, just to the south of due east. It is approaching Full tonight -- that phase officially arrives tomorrow morning. Tomorrow night the Moon rises only 23 minutes later than tonight. All week the Moon comes up less than half an hour later each night than the previous night, about the minimum possible. The average delay of moonrise from night to night over the year is about 50 minutes. Every autumn, however, the daily delay is minimal when the Moon is near full. The phenomenon is known as the "harvest moon effect." Its explanation is covered in nearly every introductory astronomy class as a way to illustrate the changing tilt of the Moon's orbit relative to our horizon.
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The Moon is Full at 9:49 a.m. EDT. Because this Full Moon is closest to the date of the Autumnal Equinox, it is known as the "harvest moon." In an earlier time, to gauge the year's passage, each full moon carried a designation indicating what events should be occurring during that time of year. The March moon, for example, was called the Sap Moon, and the Thunder Moon occurred in July. The Harvest Moon is so labeled because it rises shortly after sunset for several nights running. The light from the Full Moon allowed the harvest to continue through twilight and long into the night.
At dusk, Mars sits about 20 degrees (two fist widths) above the southern horizon. For most of the month it remains the brightest star-like object in the early evening sky. During the first part of the month, Jupiter rises as Mars sets, 4 to 5 hours after sunset, to take over as brightest. By mid month, Mars falls below Saturn's luminosity, so then you only need wait until Saturn rises, 2 1/2 hours after sunset, for Mars to be displaced as the brightest planet.
The collection of stars surrounding Mars, and particularly to its lower right, in the southern sky, belong to the zodiac constellation Sagittarius, the Archer. Faster moving Earth is pulling away from Mars, accounting for the Red Planet's slow fade. The two planets' orbital motions combine to make Mars appear to be sliding eastward (to the left) against the star patterns. Mars currently hustles along at a quarter degree per day, so if you compare its position to the surrounding stars over several days, its motion is clearly apparent. Look soon, though. Mars is entering a realm of faint zodiac constellations that will make its tracking relative to the background stars more difficult.
The waning gibbous Moon rises 2 hours after sunset, followed by Saturn an hour later. The Pleiades, or Seven Sisters, star cluster can be found 10 degrees (one fist) to the upper left of the Moon. Luna's bright glow may cause the casual observer to miss this splendid group. Binoculars are the best optical aid for gaining the cluster's full impact. The view with unaided eye is nice but not detailed enough. A telescope is too powerful -- it dilutes the sight, revealing only part of the cluster at a time.
The Moon rises 2 1/2 hours after sunset and Saturn pops up half an hour later. Once both objects are above the treeline, notice the Moon sits an equal distance (one fist) from Saturn, to the lower left, and the Pleiades, directly above. See how soon you can spot Aldebaran, the eye of Taurus, and a 1st-magnitude star, 5 degrees (half a fist) below the Moon. The sprinkling of stars between the Moon and Aldebaran comprise the Hyades star cluster which helps define the "face" of the Bull. Look for the "V" shape in a few days when the Moon is out of the picture.
Tonight Luna is 5 moon diameters to the lower left of Saturn. To see it you will need to wait 3 hours after sunset for the Moon to rise. Last night the Moon was to the upper right of the planet. During the ensuing 24 hours the Moon passed in front of Saturn, covering, or occulting, it. The event happened when neither body was visible from anywhere in the U.S. The closest place from which the occultation could be seen was western Canada.
If you are under the impression that the Moon always rises near due east, watch it come up the next two nights. Both times the Moon rises farthest north for the month, just over 30 degrees (3 fists) to the north of east. The rising direction is actually closer to NE than east. The Moon rises around 11 p.m. EDT tonight and about an hour later the following night. Jupiter is a fist width to the lower left of the Moon tonight. It rises very close to the same place the Moon does, but an hour later.
The Moon reaches Last Quarter tonight at 12:20 a.m. EDT. Technically, the date is October 10th, since the clock has crossed over by 20 minutes. The Moon rises just before then, close to midnight. Jupiter leads the show, rising about 10 minutes ahead of the Moon. The pair makes a pretty sight through daybreak. By dawn's first light the duo is two-thirds of the way up in the SE. The separation between the bodies has grown by then. The Moon pulls farther away from the giant planet by its own diameter every hour.
Observe the Moon and three planets tomorrow morning during twilight. They spread two-thirds of the way across the sky. Venus gleams brilliantly low in the east. The Moon is 50 degrees (5 fists) to the planet's upper right. Another 2 fists higher shines Jupiter, in the SE. Saturn hangs farther to the SW at about the same height as Jupiter. In your mind's eye image a great arc connecting all four objects. You are tracing the zodiac path, the plane of the solar system.
Tomorrow morning the crescent Moon is perched 11 degrees (a fist) above the star Regulus, the heart of Leo, the Lion. The head and mane of the beast are formed by a semicircle of fainter stars to the lower left of the Moon and upper left of Regulus. On some star maps, the shape, with Regulus attached, is labeled "The Sickle." To many younger stargazers who are unfamiliar with that farm implement, a backward question mark pattern is what comes to mind. The following morning (Saturday) the crescent sits below the sickle, and Regulus is 6 degrees to the Moon's upper right.
Mars reaches perihelion today. The planet's orbit is somewhat elongated and the sun is not located dead center, so one point on the path is closer to the sun than any other. Mars passes through the spot today, pulling to about 128 million miles from the sun. Halfway around the orbit is aphelion, the point farthest from the sun. Mars will be 155 million miles from the sun when it reaches that point on September 21, 2002. Earth also goes through perihelion (in January) and aphelion (in July), but the variation in sun-Earth distance is much less than for the Red Planet.
Mercury is at inferior conjunction today, which means its orbit carries the planet between us and the sun. If Earth and Mercury were in precisely the same plane, at inferior conjunction, with proper equipment, we would be able to view Mercury silhouetted against the sun's disk. Mercury's orbit, however, is tilted 7 degrees to ours, so most of the time the planet passes above or below the sun, unobserved. Today Mercury slides 1.6 degrees below the sun. Mercury travels rapidly, and in about a week the planet emerges in the morning twilight to play tag with Venus.
This morning at dawn a beautiful crescent Moon perches 10 degrees (a fist) overtop brilliant Venus. Tomorrow morning at the same time the thin Moon slips 5 degrees to the lower left of the planet and stands only 7 degrees above the eastern horizon. The Moon is then about 32 hours from New phase. The sun sits about 20 degrees directly underneath the Moon, and 12 degrees below the horizon an hour before sunup. Remember the trick to predict the sun's position: imagine using the crescent Moon as a bow to shoot an arrow at the sun. Employ this technique just before sunrise to tell precisely where the sun will rise.
With the Moon now passing out of the morning sky, the time is ideal for hunting the zodiacal light, that faint glow now seen before the start of dawn. It is created by sunlight scattered off dust particles in the plane of the solar system. Two hours before sunrise look for the ghostly pyramid rising above the eastern horizon. The vertical axis of the triangle shape will be tilted slightly toward the right (south). The zodiacal light is sometimes known as the "false dawn" because the beginning of morning twilight can easily be mistaken for the zodiacal light, and vice versa. Timing is key. For mid-northern latitudes dawn now begins 1 1/2 hours before sunrise.
The Moon is New this afternoon at 3:23 p.m. EDT. With the Moon out of the way, tonight is a good time to search for Uranus and Neptune. Both planets are among the stars of Capricornus. The faint constellation is due south at the end of dusk, about an hour and a half after sunset. Take your binoculars to a dark location with a flat southern horizon. Since Uranus is magnitude 5.8 (around the unaided-eye limit) and Neptune is 2 magnitudes fainter, you will need a good finder chart to show the way. One example of such a chart can be found at:
http://www.skypub.com/sights/moonplanets/outerplanets01.html
along with tips for "star hopping" to the planets.
The young crescent Moon will be a challenge tonight, but the sight is ample reward for the effort. Look in the WSW 30 minutes after sunset. The Moon is then only 3 degrees (6 moon diameters) above the horizon. The tips of the crescent point to the upper left. Use binoculars to help you distinguish the Moon from bright twilight background. Timing is critical, since the Moon sets an hour after sunset. A 28-hour old Moon, the age of tonight's, would be much easier to see 6 months from now. Then the tilt of the Moon's orbit is more steeply inclined to the evening horizon, so the Moon would be much higher 30 minutes after sunset.
The crescent Moon is much easier to spot than last night. It is higher at sunset, sets half and hour later, and hangs against a darker twilight. Plan to watch it long enough to enjoy the changing pallet of background colors. Tomorrow night the Moon sits 6 degrees (half a fist or 12 moon diameters) to the upper right of Antares, heart of Scorpius. So much of the scorpion has set that identifying the remaining pieces requires experience. The following night (Saturday) the Moon skips to the other side of Antares, 12 degrees (a fist) to the star's upper left.
How soon can you spot Mercury after its conjunction with the sun last Saturday? Start the quest tomorrow morning. Look just to the south of due east, 45 minutes before sunrise. Using binoculars, search 9 degrees (a fist) to the lower left of Venus. Mercury is scarcely 3 degrees above the horizon. The planet is faint -- magnitude +1.7 -- but will brighten considerably in the next week. It also sidles close to Venus, coming within a moon diameter by October 29. Plan to venture outside early enough every clear morning to catch the show. You will be rewarded with a fascinating, changing pattern.
The Orionid meteor shower reaches its peak the morning of the 22nd, but the falloff of meteor activity is slow, so the show should be near peak tomorrow morning and last through the weekend. The shower is not robust -- a meteor every few minutes on the average -- but the meteors are relatively fast, interfering moonlight is absent, and it is the weekend! Look after midnight until the approach of dawn. If you prefer a shorter viewing period, make it close to, but before, the start of morning twilight. Rather than staring in one direction, scan as much of the sky as possible, from a comfortable position.
Since June 13th, Earth has been gradually pulling away from Mars, and the planet has slowly faded in brightness. Today a milestone, of sorts, is reached. Mars is now farther from us than is the sun. The Red Planet is still brighter than any star in the current evening sky, but not for long. That waypost is passed in 3 days. Mars keeps fading through most of 2002, reaching its minimum (magnitude +1.8) in autumn of next year.
At dusk the Moon is 10 degrees (a fist) to the right of Mars. By the time the Moon sets, around 11 p.m., it will be a degree closer to the planet. As the hours pass, the Moon's orbital motion will continue carrying it nearer to Mars. The two objects pass below our horizon, but skygazers farther west around the globe will be able to watch the progress. Mid afternoon tomorrow, our time, the Moon slides less than a degree below Mars, although we cannot observe it. Planet watchers in parts of Africa and South America are treated to an occultation -- the Moon slides in front of Mars. By the time dusk approaches here tomorrow night and we can again glimpse the pair, the Moon sits 2 degrees to the planet's left.
First Quarter Moon occurs at 10:58 p.m. EDT. Mars reached its peak brightness in mid June when Earth passed closest to the Red Planet. Since then Mars has gradually faded but still remained brighter than any of the stars simultaneously visible. That record now falls. Today the planet drops below Arcturus, the brightest star visible while Mars is up and the second brightest nighttime star seen from mid-northern latitudes. (What is the brightest?)
Turn your attention to the morning skies for the next couple of weeks. Look low in the east an hour before sunrise. Venus has dominated that region for the last two months, gradually settling toward the horizon. This brightest of the planets now has a guest. Swift-moving Mercury virtually leaps out of the dawn glow to greet its brighter sibling. This morning Mercury is 3 degrees below Venus. It draws nearer by a degree per day, meeting up with Venus this weekend. There it hangs for more than a week before beginning its plunge toward the horizon. All this time Mercury continues to brighten, remaining an easy object for unaided eye until mid November.
The bright star low in the west as dusk settles in is Arcturus. Verify the star's identity by locating the Big Dipper low in the NW and using that constellation's handle to trace a curved path to the star: "Follow the arc to Arcturus." As dawn brightens, the same star can be found low in the ENE. Again, use the Big Dipper to verify it. The Dipper is now higher up in the NE, standing on its handle. Venus and Mercury, 30 degrees (3 fists) to the star's right, sit at about the same height above the horizon.
To obtain a star map showing this and other sky events, send a self-addressed, stamped envelope to Sky Calendar, Abrams Planetarium, Michigan State University, East Lansing, MI 48824.
If you have access to a telescope, you might wish to check out Jupiter tonight, particularly between 12:05 a.m. and 2:18 a.m. During that time span, the shadows of Jupiter's two closest bright moons, Io and Europa, are visible on the planet's disk. The show begins when Europa's shadow appears around 11:43 p.m., followed 22 minutes later by Io's. The two moons themselves also cross Jupiter, but they are much more difficult to see than the high-contrast shadows. Io's shadow leaves the disk at 2:18 a.m., followed by Europa's at 2:29 a.m.
Question: How can you relive an hour of your life? Answer: Stay up until 2 a.m. tonight, dutifully set your clock back to 1 a.m. at the official moment that most of the U.S. reverts to Standard Time, then do something frivolous to celebrate the opportunity of an hour regained. Never mind that you will lose the hour next April. Carpe diem.
Not to be misses: Mercury and Venus dance the tango in the morning sky. The two planets hover within a degree (two moon diameters) of one another for the next 11 days, closing to within six-tenths of a degree (1 moon diameter) for the next two days. Mercury climbs just slightly higher than Venus by tomorrow morning and remains higher until November 5. Follow the cavorting pair with unaided eye and binoculars. Look every morning you are able, an hour to 45 minutes before sunrise.
Today Mercury stands at greatest elongation (19 degrees west). To grasp the significance of this event on the planet's visibility, picture the sun in the south at midday and imagine we can see both Mercury and its orbit along with the sun. The orbit would be approximately centered on the sun and appear as a slender oval, since we see it nearly edge on. Mercury is found on the right, or west, of the sun, at the farthest extent of its orbit -- "rounding the bend" you might say. Now rotate the entire sky scene backwards toward the east, until the sun, with Mercury's orbit still centered, is on the eastern horizon. The orbit now runs more nearly up and down, with Mercury still sitting at the bend of its orbit but now above the sun and, therefore, nicely visible before sunrise.
With Mercury easy to spot, four of the five classic "naked-eye" planets are simultaneously visible 45 minutes to an hour before sunrise -- from now until Mercury drops out of sight in mid November. Start near the eastern horizon to locate Mercury and Venus together, about 10 degrees (a fist) to the south of due east and 5 degrees up. Venus is the brighter of the pair. Jupiter, brighter than Mercury but fainter than Venus, is more than two-thirds of the way up in the SW. Saturn the faintest of the group, is halfway up in the west. Orion stands about 20 degrees to the Ringed Planet's left and Aldebaran, the star marking the eye of Taurus, is perched 5 degrees below Saturn.
Halloween is one of the cross quarter days that mark the midpoints between the equinoxes and solstices. Appropriately, the Moon is Full tonight. The exact moment is 12:41 a.m. EST -- technically tomorrow morning, November 1. For timezones west of the eastern region, however, the instant of Full Moon regresses to before midnight (11:41 p.m. CST, 9:41 p.m. PST, for example), placing the Full Moon back in October and making it the second Full Moon of this month. In some circles the second Full Moon is known as a "blue moon." The origin and meaning of this designation has been of some debate. For a discussion see:
http://www.skypub.com/sights/moonplanets/mar99bluemoon.html
and
http://www.skypub.com/sights/moonplanets/9905bluemoonfever.html
Please send any comments, suggestions, or questions to
Thomas G. Ferguson:
fergus52@msu.edu
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