To the reader:
The Skywatcher's Diary for September 2004 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
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ftp://www.pa.msu.edu/pub/swd/
Skywatcher's Diary: September 2004
Follow Venus as it continues past Saturn over the next several mornings. The
change in separation of the planets is obvious from day to day as Venus drops
lower. This morning the siblings stand 2 degrees apart. In 3 days the spread
doubles to 4 degrees. Properly constructed and aligned sundials agree with
accurately set clocks today. The offset between these two modes of timekeeping,
known as the "Equation of Time," is now zero.
Be the first on your block to sight Mercury as it climbs out of the sunrise glare. The
planet comes up an hour before the sun between east and east-northeast.
Mercury shines at only 1st magnitude but brightens nearly two magnitudes (6
fold) over the next week. The planet also passes within a quarter degree of the
star Regulus a week from now, but more on that later.
Try to determine which pair of morning objects is closer, Venus and Saturn or
Pollux and Castor. The planets are easy to locate since Venus is so bright and
Saturn is directly above Venus. Look for them about a third of the way up in the
east an hour before sunrise. The star pair sits 8 degrees (less than a fist) to the
upper left of Saturn. Is your answer the same the following morning?
Globular clusters are spherical concentrations of stars that reside in the halos of
galaxies. These massive bodies contain hundreds of thousands of stars. One of
the most accessible globulars to northern observers is M13 or the Hercules
cluster. It is visible in binoculars as a faint out-of-focus spot in the constellation of
Hercules. Telescopes will resolve individual stars in the cluster. One-and-a-half
hours after sunset, the pattern of Hercules lies two-thirds of the way above the
western horizon, between the bright stars Arcturus and Vega.
You should now be watching Mercury and the star Regulus together in the
morning sky. Tomorrow morning an hour before sunrise the planet sits 4 degrees
(half a fist) above the eastern horizon, 12 degrees to the left (north) of due east.
The star, half as bright as the planet, perches 3 degrees to Mercury's lower left.
Over several mornings Regulus will seem to slide to the upper right of the planet,
passing within a quarter degree on September 10th.
The Moon reaches Last Quarter phase at 11:11 a.m. EDT. At that time the Moon
will be visible if you have a clear view of the western sky. The Last Quarter Moon
holds the distinction of being located in the direction that Earth is traveling in
space. If you are able to spot the Moon, pause long enough to image yourself,
and everything about you, hurtling toward that half-lighted orb. You will arrive there
in about three-and-a-half hours, but by then, alas, the Moon has moved on.
Tomorrow the sun's "north pole" (rotational axis) is tipped toward Earth by its
maximum extent. As we orbit around the sun, this event occurs once a year,
alternating with the south pole tilted toward us at the in-between intervals. So we
can conclude that the Earth's orbit is not exactly perpendicular to Sol's spin axis.
That should not surprise us since the other planets' orbits do not lie exactly in the
plane of Earth's orbit.
Look for the crescent Moon tomorrow morning before sunrise. It perches halfway
up in the east. Six degrees (12 moon diameters) to its left are the Gemini Twins,
stars Pollux and Castor. Saturn hangs 8 degrees below and slightly right of Luna.
Another 8 degrees to the lower left of Saturn is brilliant Venus. The following
morning (September 10) the Moon hops between the two planets and to their left.
This morning before the sun rises, Mercury and the star Regulus lie only seven-
tenths of a degree (slightly more than a moon width) apart. Look for them low
near east-northeast an hour before sunup. Brighter Mercury appears to the upper
right of the star. Tomorrow morning you won't want to miss the closest passage
of these two bodies, only two-tenths of a degree (less than half the moon's
diameter) apart. Binoculars will enhance the view.
After Mercury and Regulus' closest approach this morning, watch the pair quickly
separate over the next several mornings. The crescent Moon is dropping toward
them as well. Tomorrow morning Luna perches 10 degrees (a fist) to the lower
left of Venus. The following morning the Moon hangs 8 degrees above Mercury,
and the next morning (September 13) it slides 4 degrees to the lower left of
Mercury.
With all of the focus on planets in the morning sky, you may be wondering about
the evening planets. The sad news is there are none and there won't be any until
around New Years when Saturn begins showing up low in the east a couple
hours after sunset. That's not to suggest that you can't enjoy evening sky
watching. Some of the greatest celestial scenes occur in the autumn and winter
night skies. It's just that this year none of them will include planets.
Venus is currently passing the Beehive, or Praesepe, star cluster in the morning
sky before sunup. This collection of stars is just visible as a smudge to the
unaided eye in a dark sky. Binoculars reveal a "swarm" of dozens of faint stars. To
locate the cluster, put Venus on the right side of the field of view of your
binoculars. This morning the Beehive should appear on the left. Tomorrow the
group sits to the upper left of Venus. It's best to look before dawn, 1 1/2 hours or
earlier before sunrise.
The elusive zodiacal light is a faint shimmering of sunlight reflected off dust
particles in the solar system. It is easiest to observe when the zodiac band of
constellations stands most upright just before dawn or after dusk. This time of
year the zodiacal light appears best in predawn skies during the dark of the Moon,
which begins now. Look for a dim triangular glow rising out of the east and tilted
slightly to the right. Use the planets Mercury, Venus, and Saturn as a guide, since
they appear in the zodiac.
The Moon turns New this morning at 10:29 a.m. EDT. Rosh Hashanah, the
Jewish New Year, begins with the first sighting of the crescent after this New
Moon. Tonight the Moon is too young to be glimpsed. The record for unaided eye
sighting is just over 15 hours. Tomorrow night it will still be somewhat difficult, but
clearly possible with good sky conditions. Look very low just to the south of west
25 to 30 minutes after sunset.
Although Mercury reached its highest point above the eastern horizon for its
current morning appearance a few days ago, the planet continues to brighten and
add interest to the morning dawn. Its pace of descent quickens, however, so look
soon. The planet disappears the last week of the month. Can you spot the star
Regulus, now 7 degrees to the upper right of Mercury?
Tonight the star Spica provides a test of eyesight. Spica is a 1st-magnitude star in
Virgo, so under normal conditions you'd have no difficulty seeing it. The star
currently sets about an hour after sunset, making it hard to spot in the bright
twilight. But tonight the Moon guides you. It sits 2 degrees (4 moon diameters) to
the upper left of the star. Try to locate Spica with just your eyes. Use binoculars
only if you are unsuccessful. About 40 minutes after sunset is the optimal time.
The asteroid Vesta reached opposition a few days ago, which means now is an
ideal time to seek out the 6th-magnitude minor planet. Tonight is particularly
favorable because Vesta passes between two 5th-magnitude stars that sit a little
less than a degree apart. The stars are Omega 1 and Omega 2 in Aquarius. The
pair rises about 30 minutes after sunset, so they'll be up high enough to observe
conveniently 2 to 3 hours after sunset. Consult a detailed star chart to locate the
Omega stars. Binoculars will help locate Vesta, closer to the lower member of the
pair.
An alluring little pattern of stars in the evening sky goes by the nickname "coat
hanger" to most amateur astronomers. The reason for the name becomes
obvious when you observe the group with binoculars. The naked eye shows them
only as indistinct fuzz. A telescope reveals too many stars that obscure the
pattern. As Goldie Locks might say, binoculars are just right. To find the Coat
hanger, scan from Altair toward Vega, both bright stars in the Summer Triangle.
Move slowly, and about a third of the way along that line of sight you will bump into
an unmistakable upside down hanger.
The star 3 1/2 degrees to the left of tonight's Moon is Antares, heart of the
scorpion. Antares is a magnificent red supergiant, similar to Orion's Betelgeuse
although perhaps not as well known. Antares is a massive star nearing the end of
its existence as we currently recognize it. Soon, astronomically speaking, the star
will explode as a supernova, spewing most of its contents into space, which over
time will mix with other gas and dust and create new generations of stars.
Astronomers often talk about seasons on Mars, but they aren't referring to the
change of vegetation that we're familiar with on Earth. After all, we know plant life
does not exist on the Red Planet. Instead, astronomers judge seasons on Mars
by the tilt of its axis. Today marks the summer solstice for Mars' northern
hemisphere. The Martian North Pole is tipped its maximum extent toward the sun.
The two Mars rovers, Spirit and Opportunity, are both situated slightly below the
equator so at those sites it's technically the beginning of winter.
The Moon reaches First Quarter this morning at 11:54 a.m. EDT. By the time you
see Luna tonight, the phase should appear slightly more than half full. If you
haven't examined the Moon with binoculars in a while, take a moment to scan the
surface. Notice how the craters are more prominent near the southern (lower)
end of the terminator, as well as the great circular basins that appear darker gray
to the eastern (right) side of the Moon. To sharpen the image, brace yourself and
arms against a building or attach the binoculars to a tripod.
Welcome to autumn (northern hemisphere). The equinox occurs at 12:30 p.m.
EDT (just after noon). The Earth's axis is now tilted neither toward nor away from
the sun. Day and night are equal in length everywhere on Earth, that is, if you
ignore the refractive effect of our atmosphere. Henceforth the days shorten but the
nights grow longer, providing more time to star watch.
The bright star that's most obvious in the west as the sky darkens is Arcturus in
the constellation of Bootes (boh OH teez), the Herdsman or Bear Driver. Those
designations comes from the constellation's position behind the bear, Ursa
Major, or the Big Dipper. As the Dipper circles the northern sky, Bootes follows.
The star's name, Arcturus, also refers to the animal. It derives from "arktos," the
Greek name for bear.
The constellation low in the south 2 to 3 hours after sunset is one of the faint
zodiac patterns. Although Capricornus contains no stars brighter than 3rd
magnitude and most are 4th, the shape is distinctive and easy to find if the sky is
dark. "Chevron," "bikini bottom," and "Cheshire cat's grin" are among the ways the
outline has been described. Tonight the Moon is in the vicinity, which is good and
bad. It tells you where to look but is too bright to allow you to see the pattern well.
The northern constellation of Cepheus (SEE fee us) stands highest over the
North Star after twilight ends. The primary pattern is composed almost exclusively
of 3rd-magnitude stars. While mythologically it represents the King of Ethiopia,
the shape often suggests a child's drawing of a house. Facing north, the peak of
the roof points down, just to the upper right of the North Star. Cepheus is a
companion to the better-known constellation Cassiopeia, the Queen of Ethiopia.
A "gem" of a star is located in Cepheus. The "Garnet Star" was so named by 18th-
century astronomer William Herschel because of its clear red color. The 4th-
magnitude star is extraordinary. It's a supergiant like Betelgeuse and Antares.
The star's so large that if it took the sun's place, its atmosphere would extend to
Saturn. The star is visible to the unaided eye in a dark sky. On a star chart it may
be labeled as "Mu." Its distinctive color is the best clue for finding it. Binoculars
enhance the color even further.
The Great Square of Pegasus is now placed "squarely" in the eastern sky as
night falls. That means that the Andromeda Galaxy is also favorably located for
viewing. Using binoculars, scan the sky a third or more of the way up in the
direction east-northeast. From the suburbs, you are looking for a smudgy spot
that's slightly oval. In the country, the galaxy can nearly fill the binoculars' field of
view.
No other Moon is as well known, it seems, as the Harvest Moon. To most people
the term suggests a large, orange orb, but size and color have nothing to do with
the name. Around the Autumnal Equinox (in the northern hemisphere), the Moon's
orbital path lies relatively flat along the eastern horizon. As the Moon travels along
the orbit, each night the Moon is only slightly farther below the horizon than the
previous night at the same time. Therefore it rises not much later than the
previous night. The effect produces bright moonlight during darkening twilight for
several nights in a row -- quite a boon for farmers running late gathering in the
harvest.
Do you remember that when the month started we were talking about Mercury and
the star Regulus passing close to one another? Now in the predawn sky, Mercury
has disappeared, but Regulus is easy to spot 24 degrees (2 1/2 fists) up in the
east, and it soon has a close encounter with another planet. Regulus lies only 4
degrees to the lower left of brilliant Venus. These two objects, Venus and
Regulus, continue approaching and pass within half a moon diameter of each
other on the morning of October 3.
As you sneak a quick look at the planets in the eastern morning sky while getting
ready for the day, turn 90 degrees to the right and cast an admiring glance toward
the bright wintertime stars of Orion and friends. It's not necessary to spend much
time to take in the spectacular celestial scenery. This is only a preview. The entire
cast appears at a more convenient evening hour in just a few months.
Please send any comments, suggestions, or questions to
Thomas G. Ferguson:
fergus52@msu.edu
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