Abrams Planetarium Skywatcher's 
Diary
September
2003

To the reader:

The Skywatcher's Diary for September 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 September issue, please send a long, self-addressed stamped envelope to:

September 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/

Monday, September 1

If you regret missing Mars on August 27, its day of closest approach, thereıs still time to see Mars in its glory. Although Earth is now pulling away from Mars, we are still closer to the Red Planet than weıll be for almost 50 years. Observers with moderate amateur telescopes will continue to get nice views of Mars through the end of the month, as atmospheric conditions permit. Mars will persist as a beautiful sight to unaided eyes throughout the autumn evening skies.

Tuesday, September 2

The Moon is just shy of First Quarter this evening. It sits in the head of the scorpion. The bright star 7 degrees (almost a fist width) to Lunaıs left is Antares, heart of Scorpius. The fainter star about two moon diameters to the right of the Moon is Dschubba or Delta in Scorpius. Dschubba usually shines at magnitude 2.3. In recent years the star has brightened to almost 1st magnitude. The star spins rapidly, and the brightening is possibly associated with material being flung off the whirling sphere.

Wednesday, September 3

The Moon passes First Quarter phase this morning at 8:34 a.m. EDT, so tonight it should appear slightly more than half full. The reason the term "quarter" is used for this shape rather than "half" is because the Moon has traveled one quarter of the way through its cycle of phases. Tonight the Moon sits within the boundaries of the constellation Ophiuchus (off-ee-YOU-kuss), the Serpent Charmer. This pattern is part of the modern astronomical zodiac, although not usually recognized by astrologers.

Thursday, September 4

Around mid morning the Moon crosses the boundary from Ophiuchus to Sagittarius, the Archer. It will stand among the stars of this constellation for the next two nights, sliding approximately one moon diameter eastward against the starry background each hour. About the time Luna rises two nights from now, an hour before sunset, it passes into Capricornus, next constellation in the zodiac pathway.

Friday, September 5

An hour before sunrise, Saturn is the lone planet in the morning sky. Look for it halfway up the east-southeast. Although the planet shines at zero magnitude and is easy to spot, it is not the most luminous object up at that moment. Since the sun hasnıt yet risen and the Moon already set, the brightest object must be a star. Can you guess which one? An hour before sunrise it perches 15 degrees above the southeastern horizon. Itıs in the constellation of Canis Major. Thatıs it, the brightest nighttime star, Sirius.

Saturday, September 6

Jupiter is beginning to climb out of the sunıs glare. If youıd like to be the first on your block to witness Jupiterıs return to the morning sky, arm yourself with a pair of binoculars and venture to a locale with a flat eastern horizon. Youıll need to be in place 45 minutes before sunrise. At that time Jupiter appears only 2 degrees above the east-northeast horizon (more precisely, 14 degrees to the north (left) of due east). The star Regulus sits 2 degrees to the upper right of the planet. If you donıt have any luck at first, keep at it each clear morning. Jupiter rises 3 minutes earlier while the sun rises a minute later each day, so soon you will succeed.

Sunday, September 7

How soon after sundown can you spot Vega, the brightest of the three stars that comprise the Summer Triangle pattern? As evening twilight descends, Vega appears very near overhead. Once youıve captured Vega, watch for the other two tips of the triangle to emerge. Altair is second brightest and will appear almost halfway between Vega and the Moon, which is low in the southeast. Deneb, the faintest of the trio, lies about 2 fist widths from Vega toward the east-northeast.

Monday, September 8

The gibbous Moon rises just before sunset tonight, followed shortly by Mars to its lower left (use binoculars). Once the pair gets above the tree line, an hour or so later, youıll be able to more easily verify that the planet sits 6 degrees (12 moon diameters) away from Luna. These two solar system objects form a nearly equilateral triangle with a third -- the planet Uranus. This faint giant lies above Mars and to the upper left of Luna but will require optical aid. If you wish to locate Uranus, use a finder chart once the Moon leaves the vicinity in a few days.

Tuesday, September 9

If you were up this morning in the wee hours, you may have noticed the Moon and Mars within about 5 moon diameters of each other. The show ended not too long after 5 a.m. when the pair set in the west-southwest. Tonight during dusk you can look low in the east-northeast and verify that the Moon has traveled farther east of Mars during the daylight hours. The two bodies are separated by 8 degrees (16 moon diameters) at the end of twilight.

Wednesday, September 10

The Moon becomes exactly full today at 12:36 p.m. EDT. Since this Full Moon occurs closest to the first day of autumn, it is traditionally known as the Harvest Moon. Contrary to common understanding, the Moon will not appear larger or more red than usual when it rises around sunset tonight. The primary observable effect related to the Harvest Moon is the fact that it rises only shortly later each night -- 20 to 25 minutes later at mid northern latitudes -- for the next several nights.

Thursday, September 11

Mercury has just passed inferior conjunction, as the speedy planet slipped unnoticed about 3 degrees under the sun. The term "inferior" denotes that the planet traveled between the sun and Earth. Mercury currently lies 59 million miles (5 light minutes) from us and 35 million miles (3 light minutes) from the sun. The planet is moving toward the morning sky and will reappear before sunrise in a little more than a week.

Friday, September 12

The sun rotates on an axis, taking about 25 days to complete one spin at its equator. (Near the poles the rate is about 10 days longer.) The rotation rate has been roughly known since the time of Galileo when observers recorded the motion of sunspots across the sunıs face. The sunıs rotational axis is not perfectly straight up and down, compared to the Earthıs orbital plane, but rather tilted about 7 degrees. Around this date the tilt of the sunıs north pole is most inclined toward Earth.

Saturday, September 13

The bright star you see in the west as dusk settles is Arcturus. At the end of evening twilight Arcturus stands about 20 degrees (two fists) up in the west. Perhaps you recall seeing the star in the east or south earlier in the year. Itıs often thought of as a springtime star, since thatıs when it shines most of the night. Soon Arcturus will move from the evening to the morning sky. Near the end of October a keen-eyed observer will be able to spot it both just after sunset and before sunrise.

Sunday, September 14

Fomalhaut is a 1st-magnitude star that doesnıt get much recognition, probably because it never climbs very high as seen from mid northern latitudes. If youıd like to add it to your observing list, Mars provides a convenient pointer to the star. Two or three hours after sunset, once Mars and the star have gotten to a convenient height, locate the planet in the southeast. Fomalhaut sits 15 degrees below and slightly left of Mars. The star is the brightest object in that part of the sky, aside from Mars, which is significantly brighter and tinted orange.

Monday, September 15

Tomorrow morning before sunrise, while the sky is fairly dark, locate the Pleiades star cluster. It sits 5 degrees (10 moon diameters) above Luna. Use binoculars to get a better view of the cluster, particularly if moonlight glare makes the group difficult to see with unaided eye. Aldebaran, orange eye of Taurus, the Bull, is the star 14 degrees to the Moonıs left.

Tuesday, September 16

The gibbous Moon rises well before midnight in the east-northeastern sky. By dawn tomorrow it stands high in the southern sky. The star Aldebaran hangs 7 degrees (14 moon diameters) below it and the Pleiades cluster is found 10 degrees to the upper right of Luna. Tomorrow night the Moon comes up about 30 minutes later and by the following morning it sits almost between the stars that mark the horn tips of Taurus the Bull. Second-magnitude Elnath, the brighter horn, is perched 3 degrees to the Moonıs upper left, while 3rd-magnitude Zeta is almost twice that distance to the lower left.

Wednesday, September 17

Capella rises in the north-northeast as dusk settles in. The bright star is part of the constellation Auriga (aw-RYE-ga), the Chariot Driver. If your northern horizon is unobstructed, watch for the star to appear. The star twinkles and flashes colors at you when itıs low to the horizon -- a light show thatıs created by the Earthıs turbulent atmosphere when the starlight passes through it. Binoculars enhance the effect.

Thursday, September 18

The Moon reaches Last Quarter at 3:03 p.m. EDT. It rises about 5 hours after sunset tonight. In the early evening, before the Moon comes up, try to find a dark spot from which to view the Milky Way. If a short trip will get you to a darker site, you should consider traveling. Currently the Milky Way is almost perfectly situated for best naked eye viewing at the end of dusk. The faint, billowing star clouds of our galaxy rise up out of the southwest, pass overhead through the Summer Triangle, and descend into the northeast.

Friday, September 19

Before sunrise this morning, the fat crescent Moon stands 9 degrees (a fist) to the upper right of Saturn. Tomorrow morning look for the Moon 6 degrees to the left of Saturn. The planet now shines at a respectable magnitude zero and should reveal the hint of yellow to your gaze. Both objects, Moon and Saturn, remain in the constellation Gemini. The Twinıs two brightest stars stand vertically, 7 degrees to the Moonıs left.

Saturday, September 20

Jupiterıs becoming easier to spot low in the eastern dawn. An hour before sunup the giant planet sits 9 degrees (a fist) above the horizon. The planet Mercury begins its best morning appearance of the year. Once youıve picked out Jupiter, direct your gaze 7 degrees lower, barely above the horizon. Although Mercury will be brightening rapidly, itıs now only 1st-magnitude, so use binoculars if you donıt see it in the twilight.

Sunday, September 21

Early risers have been treated to a beautiful display of the "winter stars" for some time now. Magnificent Orion stands at attention near south. His faithful dogs, Canis Major, marked by star Sirius, and Canis Minor, with Procyon, sit to the east (left) of their master, obediently waiting a command. Those two stars, Sirius and Procyon, form an equilateral triangle with the right shoulder of Orion, the famous red giant Betelgeuse.

Monday, September 22

Autumn officially begins for the Northern Hemisphere tomorrow morning at 6:47 a.m. EDT, while spring commences for our southern cousins. At that moment the sun crosses overhead at the equator passing from north of the imaginary line to south of it. The place on Earth directly below the sun during the critical time is in Africa. For that instant the sun will shine straight down on the inhabitants of western Congo.

Tuesday, September 23

Look for the thinning crescent Moon in the east tomorrow morning before sunrise. Bright Jupiter hangs 15 degrees (1 1/2 fists) to the lower left of Luna. Fainter Mercury sits another 7 degrees below and left of Jupiter. The following morning the Moon slides down between Jupiter and Mercury and to the left. Itıs the last easy opportunity you have to see the sliver of Moon before it turns New.

Wednesday, September 24

Although the Moon becomes New tomorrow night, you have a chance to observe it tomorrow morning, about 16 hours before it turns that phase, in the eastern U.S., and 13 hours for the west coast. Optimum time to spot the hairline crescent is about 30 minutes before sunrise. Since the Moon will hang just a few degrees above the horizon, pick an observing location with a level view. The Moon will appear a few degrees to the north (left) of due east. Search with binoculars, and then once you find it, try to confirm the sighting with unaided eye.

Thursday, September 25

Although itıs been almost a month since Marsı closest approach, the planet still gleams at magnitude ­2.3. It continues to dazzle naked eye observers with its brilliant yellow-orange presence and offers good views to observers with moderate telescopes. Since it now rises an hour before sunset, the planet reaches its highest point due south before midnight -- more reasonable than the 2 a.m. transit time observers faced last month.

Friday, September 26

The Moon and Venus present an observing challenge this evening. The two objects are slightly more than a degree (2 moon widths) apart but extremely close to the sunıs direction. To have a chance to spot them, youıll need to look just after sunset -- 15 minutes after is probably optimum. At that time Venus sits 1 1/2 degrees above the horizon 7 degrees to the south (left) of due west. A pencil line crescent Moon perches just above the planet.

Saturday, September 27

Mercury reached greatest eastern elongation yesterday, that is, itıs "rounding the bend" in its orbit as seen from Earth. The elusive planet has now reached magnitude ­0.3. It is bright enough and high enough in the morning sky that anyone who has a low eastern skyline and is willing to get up early will be able to find it. An hour before sunrise Mercury sits 5 degrees above the horizon 4 degrees to the north (left) of due east and 9 degrees (a fist) to the lower left of brighter Jupiter.

Sunday, September 28

The crescent Moon is a splendid sight the next few evenings. Tonight 30 minutes after sundown look for it 9 degrees (a fist) above the southwestern horizon. It sits among the faint stars of the constellation Libra, the Scales. As the sky darkens you might wish to try finding Alpha in Libra. The star is only 3rd magnitude and would normally be challenging. Tonight the Moon sits less than a degree below Alpha, so it points the way to the fainter companion.

Monday, September 29

Today the Winter Solstice occurs for the Northern Hemisphere -- of Mars. The event is noteworthy to telescopic observers because many of them have been carefully watching the planetıs south polar cap, the white dot most prominent during the close approach. Winter in the north means summer in the south, so that cap has been significantly shrinking. Mars also reaches its stationary point today, coincidentally. That means the Red Planet has completed its retrograde motion for this opposition. Mars henceforth travels direct (eastward) until 2005 when it next approaches close to Earth.

Tuesday, September 30

The crescent Moon sits in the southwest near the end of dusk. As the sky darkens, locate the bright star 4 degrees (8 moon diameters) to the lower right of Luna. An hour after sunset is a good time to look; much later and the star gets lost in the thick atmosphere of Earth near the horizon. The star is Antares, heart of Scorpius, a red giant beauty. If the night is clear, you will likely be drawn to Antares by its orange hue and rapid twinkling. It reminds some of a flashing gemstone.

Please send any comments, suggestions, or questions to
Thomas G. Ferguson: fergus52@msu.edu