The Skywatcher's Diary for September 2006 has been prepared by Robert C. Victor, formerly Staff Astronomer (now retired). 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
(a back issue for May 2006, with the star chart May Evening Skies, is now on line.)
If you would like a printed sample of the September issue, please send a long, self-addressed stamped envelope to:
September Sky Calendar
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
Prelude to this month's Diary: What's special about the Moon in 2006?
Every year, the Sun ranges far north and south, in step with the seasons. In June the Sun rises far north of east, climbs nearly overhead at midday, and sets far north of west. In December the Sun is noticeably lower in the south at midday, and the rising and setting places are shifted well to the south of east and west. The Moon's path through the sky undergoes similar changes, but within 27 to 28 days instead of 365. And this year, the Moon ranges as far north and south as it ever does — and noticeably farther than the Sun. The Moon's journey through the northernmost constellations of the zodiac, Taurus and Gemini, is about 5 degrees north of the Sun's path, bringing the Moon unusually close to stars such as Pollux and Beta Tauri. Even the Pleiades cluster, 4 degrees north of the ecliptic, is occulted by the Moon this year. The current path of the Moon through the southern constellations of the zodiac is 5 or 6 degrees south of the Sun's, causing the Moon to track south of Antares for North American observers and through the stars of the Teapot of Sagittarius instead of well above them.
Even casual observers not familiar with constellations may notice, frequently this year, the Moon rising and setting far to the north or south of east and west, or passing unusually high or low across the southern sky. At about 27-day intervals the Moon completes a circuit among the stars, from northernmost extreme to southernmost two weeks later, and around to the northern extreme again. These special dates are noted in the Skywatcher's Diary, with suggestions of what to look for, relating to the Moon's position in the sky. Observers can get rising, transit, and setting times of the Sun and Moon for their own locations conveniently from the Astronomical Applications Department of the U.S. Naval Observatory, at http://aa.usno.navy.mil/data/
The regression of the nodes of the Moon's orbit carries the nodes (N to S and S to N ecliptic crossing points) westward completely around the zodiac in 18.6 years. Currently the ascending node of the Moon's orbit is near the Vernal Equinox in Pisces, maximizing the inclination of the orbit to Earth's equatorial plane and the Moon's wanderings north and south. But about 9 years from now, in 2015, the ascending node will be near the autumnal equinox in Virgo, and the Moon's orbit will be inclined at a shallow 18 degrees to Earth's equator instead of this year's nearly 29 degrees. That will cause the Moon to track well south of the ecliptic through Taurus and Gemini, occulting Aldebaran instead of the Pleiades, and even to go through stars of northern Orion. The Moon will also track well north of the ecliptic through Scorpius-Ophiuchus-Sagittarius, passing widely north of Antares and the stars of the Teapot. But by 2025, the Moon's orbit will return to this year's orientation.
Pay careful attention to the Moon's position in the sky now and in the years to come, and enjoy the cycle!
The Moon is unusually low — almost 6 degrees lower than the Winter solstice (Dec. 21) midday Sun — as it passes due south shortly after sunset today, and again about an hour later on Saturday. From latitude 40 degrees north, the Moon passes less than 21 degrees up in the south on September 1 and 2. Farther north, from East Lansing, MI, the Moon climbs only 18 degrees above the southern horizon those two nights. There, the Moon reaches its high point in the south at 8:18 p.m. tonight, and from all locations almost exactly one hour later nightly through Sept. 4. An hour after sunset on Sept. 1, find the star Antares 13 degrees right of the waxing gibbous Moon, then look for bright Jupiter 27 degrees right of Antares. The Teapot of eight bright stars of 2nd and 3rd magnitude in the constellation Sagittarius appears to the left of the Moon tonight and will surround the Moon tomorrow night. Using binoculars, look for the star Spica very low in WSW 20 degrees lower right of Jupiter, and for the 3rd-mag. star Alpha in Libra just 1.7 degrees left of Jupiter. On Sept. 11 and 12, Jupiter will pass about 0.5 degree (about a moon's width) above Alpha.
On Saturday an hour before sunrise (or just after 6:00 a.m. in East Lansing), look low, north of east, for Saturn, with Venus rising just 7 degrees to its lower left.
Tonight the Moon passes due south, again unusually low, just a few minutes over an hour after sunset (18 degrees up when due south at 9:17 p.m. in East Lansing). Use binoculars to see the 3rd-mag. star Delta in Sagittarius about one degree to the lower right of the Moon's bright edge. It marks the middle star of the Archer's bow, and is also one of three stars in the spout of the Teapot. The other two are Epsilon below Delta, and Gamma to Delta's right. The four stars of the handle of the Teapot are all to the left of the Moon, and the top of the lid is above the Moon.
Tonight all eight stars of the Teapot appear to the right of the Moon. The four stars of the handle lie about 5 to 10 degrees right of the Moon, as seen from Michigan as darkness falls.
On Monday an hour before sunrise, look low between ENE and E to find Saturn with bright Venus rising just over 9 degrees to its lower left. Within the next 15 minutes, if the sky is very clear, use binoculars to look for the star Regulus, heart of Leo, just 2.3 degrees below Venus.
Tonight, as Earth passes between Uranus and the Sun, Sun-Earth-Uranus lie in a straight line. As we look toward the planet Uranus, we are facing directly away from the Sun, and the planet is said to be at opposition. The 5.7-magnitude planet can be seen with the aid of binoculars if you know where to look: 1.2 degrees east (lower left in the late evening) of the 3.8-mag. star Lambda in Aquarius. You'll need a detailed star map with Greek letter labels or a star atlas to locate this star.
On Tuesday an hour before sunrise, find Venus rising 10.5 degrees lower left of Saturn, then within 15 minutes later look for Regulus 1.2 degrees to Venus' lower right. Each morning, Saturn and Regulus appear higher, owing to Earth's revolution around the Sun. However, Venus orbits even faster than Earth, and so it appears lower each morning, and will pass on the far side of the Sun in late October. Try to catch the close conjunction of Venus and Regulus on Wednesday morning.
As the sky darkens, use binoculars to look for the 3rd-mag. star Delta in Capricornus (marking the tail of the Sea Goat) about 3 degrees to the Moon's upper left.
An hour before sunrise on Wednesday, look low in ENE to E for Saturn, then within the next quarter-hour, watch for the Venus-Regulus pair rising within 12 degrees to Saturn's lower left. They are closest this morning, with Regulus 0.8 degrees to Venus' right. Forty-five minutes before sunrise this morning, or at 6:23 a.m. in East Lansing, the Venus-Regulus pair is only 4 degrees up. Find the pair before then if you can. Binoculars will help you pick out Regulus for a few minutes until it disappears in the brightening twilight glow.
From East Lansing and other locations at similar latitudes, the nearly full Moon rises about 19 minutes before sunset, and so from places with unobstructed views toward the sunset and moonrise directions, the Sun and Moon can be seen simultaneously for a few minutes until the Sun drops below the western horizon. From East Lansing tonight, the Moon rises 17 degrees south of east at 7:45 p.m. EDT.
On Thursday low in ENE to E about 45 minutes before sunrise, Venus is nearly 13 degrees lower left of Saturn, and Regulus now appears 1.7 degrees upper right of Venus.
Full Moon occurs today at 2:42 p.m. EDT, but the Moon doesn't rise until about 7 minutes after sunset as seen from East Lansing. There, the Moon rises 7 degrees south of east at 8:09 p.m. EDT. (The calculation of the time of moonrise is for when the top of the Moon's disk begins to appear above an ideal, unobstructed horizon, so you may have to wait several minutes before you actually observe the Moon.) Does the Moon seem unusually large tonight when it first rises? The Moon always seems big when it first rises, but carefully measured photographs will show the Moon actually has a smaller angular size when it rises compared to when it's highest in the sky on the same night, when Earth's rotation can bring us nearly 4,000 miles closer to the Moon. The effect of mistaken perception is called the Moon Illusion. But the Moon does appear larger in angular size on this particular night, because at about 11 p.m. EDT the Moon is at perigee, nearest to Earth, with a distance of 221,938 miles between the centers of the two bodies.
Tonight the Moon rises shortly after sunset, and then not much later and farther north each night through Sept. 14. From the latitude of East Lansing, the Moon rises only 23 to 30 minutes later each night through Sept. 11. This succession of early evening moonrise times for several days after Full is called the Harvest Moon effect, and is the result of the moon moving farther north each evening, shortening the daily delay. (Over a very large number of days, the average daily delay in the time of moonrise is 50 minutes.)
On Friday about 45 minutes before sunup, the star Regulus can be spotted in binoculars 3 degrees to the upper right of Venus. Their separation is widening by just over one degree daily.
Tonight from East Lansing, the Moon rises at 8:32 p.m. EDT, just over half an hour after sunset. Note the Moon now comes up north of east, tonight by just 3 degrees.
This evening in East Lansing, the Moon rises 13 degrees north of east, at 8:55 p.m., still in twilight, within an hour after sunset. The Moon's rising in twilight for a few nights after Full provides light for late-working farmers to bring in the Harvest. In late winter and early spring, the Moon by two nights after Full rises well after twilight ends. The large delay in moonrise time after a Full Moon at that time of year occurs because the Moon then rises farther south each evening.
Tonight the waning gibbous Moon, 85 percent full, rises 22 degrees north of east (in ENE) at 9:21 p.m., as seen from East Lansing. That's still a little before the last glow of evening twilight has faded from the WNW horizon. Look for the 2nd-mag. star Alpha in Aries 8 degrees upper left of the rising Moon.
As the sky darkens, about an hour after sunset, look for bright Jupiter low in SW to WSW, and reddish twinkling Antares, heart of the Scorpion, 25 degrees to the planet's upper left. Tonight use binoculars to find the 3rd-mag. star Alpha in Libra about half a degree below Jupiter. This is the third time Jupiter passed this star this year. Next year, in January and August, you'll find Jupiter about 5 degrees from Antares.
Tonight in East Lansing, the waning gibbous Moon rises 30 degrees north of east at 9:50 p.m. That's nearly two hours after sunset, after twilight ends. Now the 2nd-mag. star Alpha in Aries is 13 degrees upper right of the rising Moon.
On Tuesday 1½ hours before sunrise, the Moon will be high in the southern sky, with the Pleiades star cluster 7 degrees to its upper left, and the reddish first-magnitude star Aldebaran, eye of Taurus and follower of the Pleiades, 14 degrees to the cluster's lower left.
Tonight from East Lansing, the Moon rises 36 degrees north of east at 10:26 p.m.. Use binoculars to find the Pleiades cluster 3 or 4 degrees to the Moon's upper right. By 1½ hours before sunrise on Wednesday, the Pleiades will be 7 degrees right of the Moon, and bright Aldebaran will be 11 degrees below.
Tonight, the Moon still 54 percent full and approaching its Last Quarter phase, rises nearly 40 degrees north of east at 11:11 p.m. as seen from East Lansing. Look for the Pleiades 17 degrees to the Moon's upper right, and bright zero-magnitude Capella 19 degrees to Moon's upper left. By 90 minutes before sunrise on Thursday, the Moon will be very high in ESE and just over half full. Look for the 2nd-mag. star Beta Tauri, tip of the Bull's northern horn, just 1.5 degrees lower left of the Moon's illuminated edge, and first-mag. Aldebaran 15 degrees to the Moon's lower right. From southern California, the Moon covers Beta Tauri as dawn brightens. It is rare for the Moon to be far enough north to cover that star.
Today into tomorrow the Moon is unusually far north. From East Lansing it sets nearly 41 degrees north of west today at 3:46 p.m. EDT. (If the sky is clear, the nearly half-full Moon should be easy to spot in daylight until at least 3:00 p.m.) Then the Moon rises again a few minutes after 12 midnight tonight, nearly 41 degrees north of east, at 12:04 a.m. Friday morning. The Moon then rises as a crescent, 43 percent full. It's unusual to see a waning crescent so long before the middle of the night, which occurs in East Lansing that night (because of daylight saving time and our position far west within our time zone) at 1:33 a.m. EDT.
The Moon's orbit precesses in relation to the plane of Earth's orbit and changes its inclination to Earth's equator, in an 18- to 19-year cycle. In this year of the cycle, and next in 2025, the Moon ranges extremely far north to south and back again every 27 or 28 days. Tonight's moonrise at 12:04 a.m. in East Lansing is the farthest north of any for 18-19 years past and future. The Moon will climb highest, nearly 76 degrees above the southern horizon, or just over 14 degrees south of overhead, at 8:24 a.m. Friday, just over an hour after sunrise. In a dark sky 90 minutes before sunrise on Friday, note the two 3rd-mag. stars Eta and Mu Geminorum in Castor's foot 6 degrees lower right of the Moon. The "Twin" stars Pollux and Castor are within 20 degrees to Moon's lower left. The Moon sets Friday, 40 degrees north of west, at 4:40 p.m. From rising to setting on Friday, the Moon is up for 16 hours 36 minutes. (This will be exceeded by 3 minutes on October 11-12.)
One and a half hours before sunup on Saturday, look for the crescent Moon halfway up the eastern sky, with the Gemini Twins stars Pollux and Castor about 6 degrees to the Moon's lower left and left.
The Moon's extreme north and south wanderings will be one of the phenomena demonstrated in the Abrams Planetarium show Sky Preview 2006-2007, to be presented one weekend only, Sept. 29-Oct. 1. See Sept. 29 in this diary for more information.
About 90 minutes before sunrise on Sunday, the waning crescent Moon is nearly due east, 35 degrees up, with the Twin stars 7 to 11 degrees above, and Saturn 21 degrees to the Moon's lower left. Regulus, heart of Leo, is 10 degrees to Saturn's lower left. In another 45 minutes, watch for Venus rising 14 degrees lower left of Regulus.
On Monday an hour before sunrise, the crescent Moon is in the east, 30 degrees up, with Saturn 8 degrees below and Regulus 10 degrees lower left of Saturn. Within 20 minutes, watch for Venus rising 14 degrees lower left of Saturn.
An hour before sunrise on Tuesday, a beautiful thin crescent Moon with earthshine on its dark side is nearly 20 degrees up in the east. Saturn is 4 degrees to the Moon's upper right, while Regulus is 6 degrees below the crescent. Within 20 minutes, look for Venus rising 22 degrees to Moon's lower left.
On Wednesday one hour before sunrise, look for a very slender crescent Moon only 9 degrees above the horizon, 7 degrees north of due east. Saturn is 16 degrees, and fainter Regulus 6 degrees, to Moon's upper right. Within 20 minutes, look for Venus rising 11 degrees to Moon's lower left.
If you look for the Moon one hour before sunrise on Thursday, you won't see it -- it's not quite up yet! Almost directly east at that time, locate bright Saturn with Regulus within 10 degrees to its lower left. Extend the line connecting them down toward the horizon, and keep watch for the rising of a very thin crescent Moon and Venus just over a degree to the Moon's lower left.
Tonight, at 1 a.m. EDT on Friday, the Moon is at its most distant apogee of the year, at a distance of 252,587 miles from Earth. But an illuminated Moon won't be seen at all tonight or tomorrow, because it's New at 7:45 a.m. EDT on Friday. An annular solar eclipse, in which the Moon passes in front of the Sun but allows a bright ring of sunlight to show around the Moon's limb, is observable from within a track across the three Guyanas of South America, across the Atlantic, through the waters south of southernmost Africa.
The equinox at 9:03 p.m. PDT tonight (12:03 a.m. EDT on Saturday morning) marks the beginning of autumn for Earth's northern hemisphere.
Because of the timing of the New Moon and the Moon's motion steeply southward as it goes east from the Sun, the first naked-eye sighting of the evening crescent marking the start of Ramadan will likely be from Australia on September 23, where the 20-23 hour crescent will be directly above the Sun at dusk. In contrast, from East Lansing this evening, even though the Moon is 36 hours old and 16 degrees from the Sun, it is just one degree up at 7:44 p.m. EDT just 10 minutes after sunset, and will be impossible to observe. Observers across the southern U.S. from Florida to southern California have a better chance. (Using binoculars starting 15 minutes after sunset, look about 30 degrees lower right of Jupiter and 2 or 3 degrees below or lower left of Mercury.) Sightings will be easier from places farther south or west, such as Mexico, Central and South America, Hawaii, and best of all, Australia.
From East Lansing, tonight's 2½-day old Moon is a real horizon-hugger! Twenty minutes after sunset, it's only 3 degrees up in WSW. Choose a place with an unobstructed view of the horizon, and look 19 degrees lower right of Jupiter, if you can find the planet that early. Observers in southern states, where the Moon starts out higher at sunset and sets later, will have an easier time. From mid-northern latitudes, the Moon's orbit at sunset in early autumn annually reaches its minimum angle above the southern horizon, and this year (in the 18- to 19-year cycle of changes in the orientation of the Moon's orbit) the inclination of the moon's path is even worse.
Thirty minutes after sunset tonight, the Moon is just 5 degrees up in SW to WSW as seen from East Lansing, where the time is 8:00 p.m. EDT. Look 9 degrees lower right of Jupiter. Again, observers farther south will catch the Moon higher in the sky, but viewers farther north will see it even lower.
Thirty minutes after sunset, the Moon is 8 degrees up in SW as seen from East Lansing. Notice Jupiter 8 degrees to the Moon's upper right.
This afternoon just over two hours before sunset, the crescent Moon, 25 percent full, passes due south, only 21 degrees above the horizon at 5:16 p.m. as seen from East Lansing. (It'll be even lower the next three evenings.) An hour after sunset tonight, the Moon is only 8 degrees up in SW as seen from the same location. Bright Jupiter is 19 degrees to the Moon's right, while Antares, heart of the Scorpion, is just 4 or 5 degrees to the Moon's upper left. Check again tomorrow.
Today 1¼ hours before sunset, the crescent Moon one-third full passes due south, just over 18 degrees up at 6:10 p.m. as seen from East Lansing. An hour after sunset from the same place (at 8:25 p.m.), the Moon is just 12 degrees up in SSW, with Antares 8 degrees lower right.
This afternoon and evening the Moon makes a low arc across the sky which is extremely far to the south. From East Lansing, the fat crescent Moon rises 41 degrees south of east at 2:59 p.m. EDT, its southernmost rising in the 18- to 19-year cycle of variation in the orientation of the Moon's orbit. (If the sky is clear, the Moon should be easy to see very low in the SE within half an hour later.) The Moon reaches its high point in the south just over four hours later, at 7:06 p.m., when it passes not quite 18 degrees above the horizon from East Lansing. This is also the lowest Moon when directly south for the current 18-19 year cycle. Sunset occurs only 17 minutes later, at 7:23 p.m. EDT. When darkness falls about 1½ hours later, the Moon is only 14 degrees up in SSW, and the star Gamma in Sagittarius, the tip of the Archer's arrow and tip of the spout of the Teapot, is visible in binoculars just 0.6 degree (about one moon-diameter) south or lower left of the Moon's lower cusp. Finally, the Moon sets 41 degrees south of west at 11:14 p.m., the southernmost nighttime moonset of the 18-19-year cycle. From rising to setting in E. Lansing, the Moon is above the horizon only about 8-1/4 hours.
This weekend, we have scheduled public observing nights at the MSU Observatory on Friday and Saturday evenings, from 9:00 p.m. until 11:00 p.m. But since the Moon is so low and sets early, we are providing a chance to observe the unusually low Moon from in front of Abrams Planetarium those nights beginning at 7:30 p.m. and continuing until just before the 8:00 p.m. planetarium show. (On Friday, on your way here, be sure to catch the Moon as it passes due south at 7:06 p.m.) The planetarium show this weekend, Sky Preview 2006-2007, is a demonstration of the Moon's unusual wanderings in the coming months, and a preview of lunar and planetary gatherings until mid-2007, including two total lunar eclipses and a spectacular midyear evening conjunction of Venus and Saturn. Bob Victor, author of the planetarium's Sky Calendar and of the Skywatcher's Diary (on the Abrams Planetarium web site) has offered to come out of retirement for just the one weekend of Sept. 29-Oct. 1 to give the presentations. Show times for Sky Preview that weekend are, as usual, Friday and Saturday at 8:00 p.m., and Sunday at 4:00 p.m. The new Family Show, The Sky Above Mister Rogers' Neighborhood, will be presented on Sunday at 2:30 p.m. Regular Feature Shows will open the new season with the Isaac Asimov science-fiction tale, The Last Question, on Friday, October 6.
From East Lansing this evening, the Moon passes due south, less than 19 degrees up, at 8:05 p.m., nearly 45 minutes after sunset. Again, special just for this weekend of the low Moon, lunar observing will begin in front of Abrams Planetarium at 7:30 p.m. and continue until just before the 8:00 p.m. showing of Sky Preview 2006-2007. (The final showing of Sky Preview will be on Sunday Oct. 1 at 4:00 p.m.) At nightfall Saturday, the 3rd-mag. star Tau Sagittarii, in the handle of the Teapot, is visible in binoculars just above the Moon.
Please send any comments, suggestions, or questions to
Shane Horvatin: firstname.lastname@example.org