To the reader:
The Skywatcher's Diary for September 2005 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
Skywatchers Diary: September 2005
- The brilliant planetary duo, Venus and Jupiter, makes an exquisite sight low in the
west-southwest after sunset. If you've been following their motion, tonight they
appear closest, a little more than 2 moon diameters apart. The 1st-magnitude
star Spica, 5 degrees or half a fist to the pair's left, pales in comparison to the two
most luminous planets. With diligence you'll be able to watch the two planets
through the rest of this month as they separate.
- If you have access to a telescope, examine both Venus and Jupiter some night
soon. If the air is steady, you may be able to discern a difference in the shape of
the two planets. Jupiter's at full phase while Venus is currently about three-
quarters full. Notice also that Jupiter's disk appears about twice as large as
Venus'. Venus is brighter, however, because its cloud cover is more reflective.
- New Moon occurs this afternoon at 2:45 p.m. EDT. Observers in southern states
may get a glimpse of the young crescent tomorrow evening, although the rest of
the U.S. will wait until Monday. Notice how Venus, Jupiter, and Spica appear in
nearly a straight line tonight. Venus holds the center position with Jupiter to the
right and Spica slightly farther left.
- This morning, before sunrise, Mercury passes slightly more than a degree to the
upper left of the star Regulus. Mercury is in descent, heading back toward the
sun, and brightening slightly as it does. The planet reaches superior conjunction
(behind the sun on the far side of its orbit) on the 17th. Look low in the east-
northeast 45 minutes ahead of sunrise over the next several days if you wish to
catch the planet before it is lost in the solar glare.
- The first crack at sighting the young crescent Moon occurs this evening for most
of the U.S. About 30 minutes after sunset look just to the left (south) of due west.
The Moon sits 4 degrees (less than half a fist width) above the horizon. Venus
and Jupiter reside to the upper left of Luna, 15 and 11 degrees, respectively.
Notice the star Spica, less than 2 degrees to the lower left of Venus.
- Celestial Scenery Alert. Four bright objects perch within 5 degrees of one another
in tonight's early evening sky. The event is best observed about 45 minutes after
sunset. Look low in the west-southwest. Venus and Jupiter appear almost
horizontal, about 5 degrees apart. Below and between them sits a stunning
crescent Moon. Faintest of the quartet, Spica hangs 4 moon diameters directly
below Venus, the leftmost and brightest planet.
- Tonight, for your observing pleasure, the Moon, Venus, and Jupiter align. If you
have lost track of who's who in the shell game of moving planets, Venus is
brightest and centermost. Jupiter appears 6 degrees (half a fist) to the right, and
the crescent 8 degrees left. Can you spot Spica? Look 2 degrees to the lower
right of Venus.
- Mars watching is now becoming convenient. The planet rises less than 3 hours
after sunset, so it is visible before most people's bedtime. The brilliant red-
orange point of light is easy to find in the eastern sky. Mars is almost as bright as
Jupiter, and nothing in its immediate vicinity compares. The Pleiades star cluster
rises about the same time as Mars, 12 degrees to the planet's left (north).
- Perhaps you came across a hoax email regarding Mars that circulated throughout
the summer. It described an incident in late August when Mars was to appear as
bright and big as the full moon. No such event occurred, nor is it even possible.
Mars will be passing relatively close to Earth this year, but in early September. It is
already a pleasing naked-eye object and will become a reasonable telescope
target for experienced observers. More on that topic next month.
- The Moon, almost First Quarter, perches near Antares tonight. Look for the star 3
degrees (6 moon diameters) to Luna's right. Antares marks the heart of the
constellation Scorpius. Earlier in the day the Moon occulted (passed in front of)
Antares for locations in the southeastern U.S. Daytime occultations such as this
one are for experienced telescopic observers.
- The Moon reaches First Quarter at 7:37 a.m. EDT, so tonight look for it to appear
slightly more than half full. Near the time of sunset the Moon passes due south.
Take note of how low the Moon sits. Each day as celestial objects travel across
the sky they reach their highest point when they cross due south. Now watch
southern passages of Luna over subsequent nights and confirm that this
month's "lowest south" Moon occurs tonight.
- Early risers can track Saturn's progress near the Beehive star cluster over the
next few mornings. One-and-a-half hours before sunrise Saturn sits a quarter
way up in the east. The cluster will probably not be visible to the naked eye under
these conditions, so use binoculars. Tomorrow morning the sprinkling of stars
comprising the cluster sits about a degree (much less than a binocular field of
view) to Saturn's upper left.
- With the Moon waxing brighter each evening, the best dark-sky star watching now
occurs in the morning before dawn begins. The bright wintertime stars of Orion
and surrounding constellations display their allure in the southeast. The Milky
Way galaxy flows from southeast to northwest, crossing through the top of the sky.
The great Andromeda Galaxy sits high in the west.
- The spread between the evening planets Venus and Jupiter now extends to 13
degrees (more than a fist width). Forty-five minutes after sunset Venus is easiest
to locate low in the west-southwest. Jupiter stands only 4 degrees above the
horizon to Venus' lower right. The bright star Spica is still observable but only for a
few more nights. Look for it 4 degrees to Jupiter's lower left and 10 degrees to
Venus' lower right. Spica is easiest from southern states.
- About an hour after sunset the bright star Vega, part of the Summer Triangle, sits
almost exactly at the sky's zenith (overhead) for latitude 40 degrees north, and
close to the apex for the entire contiguous 48 states. If you have never tried
looking straight up, from a standing position, it's not as easy as you might think.
Try it by sighting Vega. Human anatomy, it seems, is better suited to scanning the
horizon.
- The Moon rises shortly before sunrise tonight. It sits among the stars of the
constellation Aquarius, about 3 degrees (six moon diameters) from Uranus. Alas,
the brilliance of the almost-full Moon destroys any chance of seeing much of the
faint constellation or the 6th-magnitude planet. If you wish to locate Uranus, wait
until Luna moves on and use a good finder chart.
- The Moon is exactly full tonight at 10:01 p.m. EDT. Because this is the Full Moon
that occurs closest to the Autumnal Equinox, tradition has labeled it the Harvest
Moon. Because the Moon's orbit tilts more horizontally along the eastern horizon
this time of year, the Moon rises during dusk for several nights in a row, providing
additional light to extend farmer's daily harvest time.
- The Great Square of Pegasus, stalwart of autumn night skies, sits "squarely" in
the east at the end of evening twilight. Actually, the shape might better be
described as a "diamond" this time of year because the pattern appears rotated
so that a corner of the square points downward. Each side of the square
measures about 1 1/2 fist widths. The stars are similar in brightness to those in
the Big Dipper.
- The top star in the square of Pegasus is known as Scheat (SHEE-at) or the Beta
star in Pegasus. The star is relatively cool, which can be deciphered from its color
Scheat is decidedly reddish in binoculars or telescopes. It's also quite large,
almost 100 times the diameter of our sun. Perhaps most interesting to the
amateur astronomer, Scheat varies in brightness by about half a magnitude but
not in a regular fashion a not uncommon trait among red giant stars.
- If you are looking for the Big Dipper, it's low in the northwest at nightfall. As the
night continues, the well-known pattern drops even lower, reaching its nadir after
midnight, local daylight time. All seven stars are circumpolar (never rise or set) for
about latitude 40 degrees and farther north. Alkaid, the star at the end of the
handle, is the first to lose visibility as you travel south.
- Tonight the Moon rises in the east-northeast about 2 hours after sunset. Twenty
minutes later Mars appears 5 degrees (10 moon diameters) to Luna's lower
right. The ruddy planet glimmers at a respectable magnitude 1.4. If you were to
follow the pair across the sky, by dawn the two sit high in the west-southwest 7
degrees apart. Use binoculars to pick out the Pleiades star cluster 6 degrees to
the Moon's lower left (evening), or 3 degrees upper left of Luna (morning).
- The Autumnal Equinox, first day of fall for the Northern Hemisphere, occurs at
6:23 p.m. EDT. At that moment the sun stands directly above the Earth's equator
at a point in the Pacific Ocean just south of Christmas Island. Back in the U.S., the
daily arc of the sun across the sky becomes progressively lower and shorter. We
are headed for the dark season.
- Jupiter continues to slowly fade into the sunset glow. Not many more evenings
and the giant planet will surrender to sunlight. Begin looking for it about 30
minutes after sundown low in the west-southwest. Venus will be more obvious,
21 degrees (2 fists) to the upper left of Jupiter. Forty-five minutes after sunset
Jupiter perches not quite 2 degrees above the horizon.
- You may recall that the lowest south-passing moon of the month occurred 2
weeks ago. The Moon reaches its highest perch tomorrow morning around
sunrise. The Last Quarter Moon climbs near overhead. Meanwhile, tonight's
rising Moon breaks the horizon at the northernmost spot for the month, almost
due northeast. Look for it to come up about 4 hours after sunset.
- The Moon reaches Last Quarter phase at 2:41 a.m. EDT this morning. Since this
phase rises in the middle of the night and sets around midday, it's most often
seen by people on their way to work in the morning. The position that the Last
Quarter Moon occupies in the sky marks the direction the Earth is traveling as it
orbits the sun. So when you glance at the Moon this morning, you are looking out
the "windshield" of Spaceship Earth.
- Venus, Jupiter, and the star Spica nearly align in the early evening sky. First locate
Venus 30 to 40 minutes after sunset. Next find Jupiter 24 degrees (2 1/2 fists) to
Venus' lower right. Jupiter sits very low above the western horizon. Finally, look for
Spica, 22 degrees to the upper left of Venus. The 1st-magnitude star may be
difficult to see so soon after sunset without binoculars.
- This morning before sunrise the crescent Moon sits below the Gemini Twins,
marked by bright stars Pollux and Castor, 6 degrees (half a fist) and 10 degrees
above Luna, respectively. Ten degrees below the Moon look for Saturn. Tomorrow
morning Luna slips 5 degrees to the planet's left.
- Over the next two mornings the thinning crescent Moon straddles Regulus, the
bright star that marks the heart of Leo, the Lion. Tomorrow morning the star
hangs 8 degrees below Luna. The following dawn the Moon sits 6 degrees to the
lower left of the star. While moon watching be sure to take in Orion and the
brilliant star Sirius in the southern sky. Be alert to the twinkling colors of Sirius.
- The 4th-magnitude star Eta in Cassiopeia is noteworthy. It's similar in color and
size to our Sun. So if we were to visit Eta, a relatively close 19 light years away,
and looked back in the direction of home, Sol would appear much like Eta. Where
is Eta? The star is not part of the traditional "W" pattern that we associate with
Cassiopeia, but it is easy to locate. Start with the bright end of the "W" and move
to the second star (known as Alpha or Schedar). Between the second and third
star, about one-third the way, is Eta.
- The Milky Way galaxy is nicely spread across the sky through most of the night. In
the evening it stretches from the northeast, through the zenith, and settles in the
southwest where the center of the galaxy then lies. In the morning, the
shimmering band extends from northwest to southeast. With only a sliver of a
moon appearing just before sunrise, it's a perfect opportunity to take in the
majesty of our home galaxy from a dark-sky site.
Please send any comments, suggestions, or questions to
Thomas G. Ferguson:
fergus52@msu.edu
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