To the reader:
The Skywatcher's Diary for September 2003 has been prepared by
David Batch. Credit to the author and to
Department of Physics and Astronomy at
Michigan State University, and mention of
Sky Calendar, would be
A sample issue of the Sky Calendar is available over the Internet. It
can be viewed via the World-Wide Web at
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
Current and back-issues of the Skywatcher's Diary are available in our
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.
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.
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.
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
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.
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.
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.
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.
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.
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
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.
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.
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
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.
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.
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.
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 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.
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.
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.
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.
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
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.
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.
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.
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.
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
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.
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.
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: