To the reader:
The Skywatcher's Diary for September 2002 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/
Skywatcher's Diary: September 2002
This morning before sunrise the crescent Moon sits 3 degrees (6 moon
diameters) overtop Saturn. Tomorrow morning the Moon drops to 10 degrees (a
fist) to the Ringed Planet's lower left. Today Mercury reaches its maximum
angular distance (greatest elongation) from the sun for this evening appearance.
The elusive planet's showing is poor for northern latitude observers, however. If
you enjoy a challenge, look for it 40 minutes after sunset just above the horizon,
between west and west-southwest. You will need binoculars to pick out the zero-
magnitude planet from the bright twilight. The Moon is in its vicinity next Saturday
and Sunday (September 7 and 8).
Venus passed closest to 1st-magnitude Spica at the end of last month. Forty-five
minutes after sunset tonight look for the brilliant planet only 6 degrees (half a fist)
above the west-southwest horizon. Spica sits 2 degrees to Venus' right. You may
need binoculars to initially locate the star. Follow the relative motion of the two
bodies each night, as they separate by about 1 degree per night. You will also
notice that Venus moves slightly higher than Spica, while both objects appear
lower each night at the same time. See how many days you are able to follow
Spica before it becomes lost in twilight.
The crescent Moon dissolves into dawn this week on its way to New phase on
Friday. This morning an hour before sunup the Moon is due east. The two bright
stars marking the heads of the Gemini Twins sit to its left. Pollux is 4 degrees
(8 moon diameters) due left, and Castor perches 7 degrees to Luna's upper left,
5 degrees above Pollux. Jupiter lies 16 degrees (1 1/2 fists) to the Moon's lower
left. Tomorrow morning the Moon slides to within 4 degrees of the large planet's
upper left. The following morning (Thursday, the 5th) the thin crescent will be
found 13 degrees to Jupiter's lower left.
Jupiter now rises 3 hours ahead of the sun, so it is about 15 degrees above the
horizon at the start of morning twilight. If you look with binoculars to the planet's
upper left at that time, you should be able to pick out the Beehive star cluster. The
object appears as a swarm of faint stars, which accounts for its nickname. The
group's more formal designation is Praesepe (pray-SEP-pee), which means
"manger," alluding to the birthplace of Jesus. Two faint stars flank the Praesepe,
one above and one below. In keeping with the stable theme, they are known as
Asellus Borealis and Asellus Australis, the northern and southern ass.
Experienced skywatchers prepare for an observing challenge tomorrow morning
ahead of sunrise. Thirty-five minutes before sunup the hairline crescent Moon
(less than 17 hours before New) appears 3 degrees above the east-northeast
horizon. Six degrees to its upper right sits Regulus, a 1st-magnitude star in Leo.
Three degrees to the Moon's lower right, 2nd-magnitude Mars is just emerging
from behind the sun. At that moment it stands slightly over 1 degree above the
horizon. To find all three objects, you will need binoculars, a flat horizon, an
exceptionally clear sky, and luck. Are you up for it?
New Moon occurs this evening at 11:10 p.m. EDT. This evening also begins Rosh
Hashanah, the first day of the Jewish Year 5763 A.M. Originally the Jewish year
commenced with the first sighting of the young moon after New Moon, nearest the
Autumnal Equinox. If that method were still in use, the new year would not begin
until tomorrow night -- our first chance to catch the crescent. Even then, Luna
won't be an easy target.
Look 30 minutes after sunset to catch the wisp of Moon, less than a day old (past
New phase). The extremely thin crescent then sits 2 degrees (4 moon diameters)
off the horizon and 4 degrees north of due west. If you've never seen a Moon
younger than 24 hours old, the fragile arc of light extending less than half a circle
will captivate you. Mercury hangs 16 degrees to the Moon's left, and slightly lower.
Use binoculars. Venus is farther to the left (34 degrees) and higher. Today Venus
stands at aphelion, or the farthest point in its orbit from the sun, a distance of
67,690,000 miles. That's about a million miles farther than the nearest point,
perihelion.
If you are out observing soon after sunset, the Moon will be easy tonight. Begin
looking 30 minutes after sundown. The Moon is then 7 degrees up and 9 degrees
(a fist) to the south of due west. Venus is 20 degrees to the Moon's left and at the
same height. Use binoculars to help locate the star Spica, between and slightly
below Venus and the Moon, 8 degrees to the planet's right and 12 degrees from
Luna. Mercury will be tough to spot, 7 degrees to the Moon's lower left and less
than a degree off the horizon.
Tonight the Moon hangs 8 degrees (16 moon diameters) to the upper right of
Venus. Look shortly after sunset, since Venus sets before twilight ends.
Tomorrow night the Moon scoots 12 degrees to the upper left of the planet.
Careful inspection then reveals a 3rd-magnitude star 3 degrees to the Moon's left.
The star Zubenelgenubi (zoo-bin-ell-gih-NOO-bee) belongs to the modern
constellation of Libra, the Scales. Its name, however, divulges a different history.
The name comes from Arabic and means "southern claw." It refers to the
scorpion, which present day sits immediately to the left, but at one time
encompassed Libra.
The Moon makes a wonderful binocular and telescopic object, particularly from
about 3 days after new phase through First Quarter. During this period, sunlight
hits the lunar surface at an angle that enhances the shadows of craters and other
vertical features. They appear more pronounced and easier to pick out with small
optical instruments. If you haven't gazed at the Moon through binoculars recently,
tonight's prime time. Don't limit your moon watching to just one night, though. The
daily changes are also fascinating. To see a preview of what you can expect, visit
www.pa.msu.edu/abrams/ and click on "Moon Photos."
This evening the Moon sets slightly less than 3 hours after sunset. Officially it
resides among the stars of Libra, the Scales. If you recognize any constellation in
that part of the sky, though, it probably will be Scorpius, the Scorpion, since
Libra's brightest star is only 3rd magnitude. Six degrees to the Moon's left sits the
star Delta in Scorpius (also called Dschubba). If you look up the star's magnitude
in a chart, you will probably find it listed as 2.3. Delta currently registers 1.6,
however. We are catching it in the midst of an eruption that started in 2000. Delta
belongs to a class of peculiar stars known as "Be" (pronounced "bee-ee") or
class B emission stars. The extremely hot stars all rotate rapidly, driving material
into a disk surrounding the star. The brightening of Delta is likely tied to such a
mass transfer.
The bright ruddy star 4 degrees (8 moon diameters) below the Moon tonight is
Antares, heart of Scorpius. This 1st-magnitude beauty is a distant 600 light years
from us, one of the most remote stars we can see without optical aid. The fact that
Antares appears so bright to us while at such a distance indicates that the star is
exceptionally luminous, about 17,000 times brighter than the sun, in fact. Its
reddish hue also tells us that Antares is much cooler than our yellow sun. Bright,
but cool, means the star is large Ñ a red supergiant. If placed at the sun's
position, the star's surface would extend beyond Earth, Mars, and the asteroid
belt Ñ almost to Jupiter.
Superstitions relating to both Fridays and the number 13 go back to ancient times
and are spread over several cultures. No wonder that the convergence of these
two bad-luck omens on a single day produced some serious angst among the
credulous. Friday falls on the 13th one, two, or more rarely, three times a year.
2002 harbors two of them, December being the other month. Astronomically, the
Moon attains First Quarter at 2:08 p.m. EDT Ñ nothing foreboding in that. Look for
it this evening, perched 12 degrees above the tip of the scorpion's tail.
The gibbous Moon sits in the "lid" of the "Teapot," classically known as
Sagittarius, the Archer. Look for Nunki (also Sigma) 5 degrees (10 moon
diameters) to the left and Kaus Australis (Epsilon) 9 degrees below. Both
2nd magnitude, these two stars are the brightest of the pattern. Nunki marks the
top of the teapot's handle and Kaus Australis indicates the bottom of the spout.
See if you can determine that Kaus Australis is the brighter of the two. Tomorrow
night the Moon lies 8 degrees to the left of Nunki.
The bright star near overhead as the sky darkens is Vega, the brightest member
of the pseudo-constellation, the Summer Triangle. Vega technically belongs to
Lyra, the Harp, a small, inconspicuous parallelogram shape. Vega is the fifth
brightest star in the sky (ignoring the sun) but the third brightest visible from
northern latitudes. Can you guess which two stars are brighter? Sirius should be
a "gimme," since it is often described as the brightest nighttime star. Arcturus is
the other, a third of the way up in the west during early evening. It barely outshines
Vega by only 0.08 of a magnitude.
For a star map to assist in locating Lyra and other celestial objects, send a
stamped, self-addressed envelope to Sky Calendar, Abrams Planetarium,
Michigan State University, East Lansing, MI 48824.
Twenty-four degrees (2 1/2 fists) to the east of Vega sits Deneb, the faintest of the
Summer Triangle threesome but still of 1st magnitude. The star marks the tail of
Cygnus, the Swan. A nice pair of widely spaced 4th-magnitude stars can be found
5 degrees to the northwest of Deneb. To locate them, start tracing back from
Deneb toward Vega about 5 degrees (half a fist), then look north of the line. The
two stars appear similar in brightness and color, and separated by 1 degree (a
finger width). Omicron1 and Omicron2 are their official designations. Examine the
southernmost component (Omicron1) with binoculars to discover a 5th-magnitude
companion a tenth of a degree away. A small telescope reveals yet a third,
7th-magnitude star closer to Omicron1. The group makes a pleasing sight that's
within the reach of unaided eye and modest equipment.
The Moon is between 10 and 11 days old tonight, so its profile is clearly gibbous.
Full Moon is still more than 3 days away. Although the binocular or telescopic view
reveals fewer craters than earlier in the month, several objects make the sight
worth the effort. On the upper left portion of the Moon's face, look for a bright crater
sitting almost alone amidst a dark surface. The crater is Copernicus, named for
an early renaissance astronomer who promoted a sun-centered rather than
earth-centered solar system. Another prominent crater lies near the bottom 5th of
the Moon and is distinguishable by the bright streaks radiating out from it to great
distances across the surface. This crater Tycho honors another 16th century
astronomer Tycho Brahe. Brahe was a meticulous observer who amassed
accurate data that were later used, most notably, to establish the elliptical orbit of
Mars.
The morning skies are moonlight free for several more days, so if you have
access to a dark observing site, remember to look for the zodiacal light. Observe
before twilight begins, so that you don't confuse the two similar effects. Look not
later than about 5:30 a.m. The zodiacal light is produced when dust particles in
the solar system scatter sunlight. It is most pronounced near the direction of the
sun but can only be seen when the observer is in complete darkness. Hence the
necessity for an early morning wakeup call. If you simply cannot function at that
hour, take heart. Evening opportunities to catch the phenomenon occur each
spring.
Both Saturn and Jupiter are well placed for observing before sunrise. The Ringed
Planet rises just after midnight, so it has plenty of time to climb the eastern sky
before morning. At the beginning of dawn, Saturn sits two-thirds of the way up in
the southeast. By then, brighter Jupiter is about a third of the way up in the east. It
rises 4 hours ahead of Sol. Mars is beginning its return to the morning, but the
now 2nd-magnitude planet fights a tough battle against the bright twilight, since it
rises scarcely an hour before sunup.
The sky just before dawn is ablaze with the magnificent stars many of us love to
observe on a winter's evening. The "Winter Ellipse" encompasses most of these
constellations: Orion, Canis Major, Canis Minor, Gemini, Auriga, and Taurus.
Don't neglect the Hyades and Pleiades star clusters, the famous dust cloud
known as the Orion Nebula, and the Milky Way that stretches from southeast to
northwest. Here's the opportunity for northern skywatchers to welcome these
glorious sights without the need for hats, mittens, and winter coats. Rousing early
out of bed would seem a small price to pay.
Full Moon occurs at 9:59 a.m. EDT. In colonial times, the Full Moon of September
was known as the Fruit Moon. This year it has an additional designation: Harvest
Moon. While we frequently associate October with harvest time, the Harvest Moon
is linked to the first day of autumn. Officially defined as the Full Moon that occurs
closest to the Autumnal Equinox, it can range from the first week of September
through the first week of October. This year the equinox takes place two days from
now, on the 23rd. The Harvest Moon was given its name because for several
nights in a row the moon rises in twilight, and thereby provides continuous
illumination to carry on the harvest after dark. The Harvest Moon is not unusually
large or particularly red!
Saturn now rises before midnight. It comes up about 4 minutes earlier per day, so
a week from now you'll see it peeking above the east-northeastern horizon half an
hour sooner. A month from now it will rise near 10 p.m. The planet officially sits
within the boundaries of the constellation of Orion, but its position is where Orion,
Taurus, and Gemini come together, near the horns of the bull and the feet of the
twins. In early October it begins its westward (retrograde) wandering relative to
the stars, and by the end of the year passes close to one of Taurus' horn tips.
The Autumnal Equinox occurs at 12:56 a.m. EDT, officially marking the start of fall
for the northern hemisphere and spring for our friends below the equator. The
timing, less than an hour after midnight, may cause confusion if you acknowledge
the date with family and friends that live in a time zone west of Eastern. The
equinox is an event that occurs at the same instant all over the globe, so the local
circumstance depends on your time zone, similar to the New Year's celebration.
The moment of equinox is reckoned an hour earlier for each time zone farther
west. For Central Time and zones farther west, therefore, the equinox really
occurs on Sunday night, the 22nd.
Several days ago Mars reached the point in its orbit farthest from the sun
(aphelion), about 155 million miles. Eleven months from now Mars will be closest
to the sun (perihelion, 128 million miles). The orbit of Mars is more elongated
than all of the planets except Mercury and Pluto. Mix that with the planet's extreme
changes in its distance from Earth, and earthlings enjoy dramatic variations in the
Red Planet's appearance. Currently Mars is near its greatest distant from Earth,
so we see the planet at a dim, magnitude 1.8. Next August Mars approaches
within 35 million miles of us, by a statistical quirk closer than it's been in
thousands of years. The planet will reach magnitude Ð2.9, exceptionally bright
and an enormous change in 11 months. Try to catch Mars some morning in the
next few weeks as it emerges out of the dawn twilight. Look low in the east
45 minutes to an hour before sunup. Then file the image away in you memory to
be used for comparing to Mars in August of 2003.
Venus now shines at magnitude Ð4.6, its greatest brilliancy during this evening
appearance. The luminosity of Venus is a playoff of primarily two conditions: its
distance from Earth, and how much of its illuminated surface we can see, that is,
its phase. The larger the phase and the closer to us, the brighter Venus appears.
Venus is currently pulling nearer, but the phase is shrinking. The tradeoff reaches
maximum at this time. Your unaided eye won't notice any difference, but take a
look tonight, anyway. Better yet, find Venus just before sunset when the planet is
higher in the west and you will be better able to see its 25% phase in binoculars
and telescopes. Look in the southwest, about 40 degrees (4 fists) to the left of the
sun and 10 degrees higher.
Tomorrow morning the waning gibbous Moon is found among the stars of
Taurus. The bright star 5 degrees (10 moon diameters) to the Moon's lower left is
Aldebaran, eye of the bull. The fainter star only 2 degrees in the same direction is
Epsilon, the other eye. Falling away to the lower right of those two stars is a
V-shaped pattern usually thought of as the face of Taurus. It is comprised
primarily of stars from the Hyades star cluster. The Pleiades, another, tighter star
cluster, sits 9 degrees to Luna's right. The glare of moonlight may conceal these
clusters at first glance. Notice how high the Moon appears the next several
mornings. It's more than two-thirds of the way up an hour before sunrise.
The Moon hangs 9 degrees (a fist width) to the right of Saturn tomorrow morning.
By Sunday before sunup, Luna slides 5 degrees to the upper left of the Ringed
Planet and advances toward Last Quarter. That phase occurs during midday on
Sunday. If you have access to a telescope, be sure to examine Saturn sometime
soon. Sunlight falling on the planet produces an obvious shadow on the rings.
The dark band creates a visual gap between the rings and planet where the rings
pass behind the planet's disk. The effect is to add depth to the view, giving Saturn
a stunning three-dimensional quality. The effect continues through mid October,
but diminishes the longer you wait.
Tomorrow morning Saturn sits 5 degrees (10 moon diameters) to the right of the
Moon as dawn arrives. The following morning (Monday) look for the Moon within
the constellation of Gemini, near the two bright stars Pollux and Castor. Pollux
can be found 8 degrees to Luna's lower left. His brother Castor is 8 degrees to
the upper left of the Moon. Five degrees separate the stars. Pollux is officially a
1st-magnitude star while his brother is only 2nd magnitude. That description
makes it sound like Pollux is considerably brighter, but if you observe the pair
you'll see the luminosity difference is subtle. The truth lies in number round off.
Pollux is magnitude 1.16, and Castor is 1.58, which rounds to 2nd magnitude. The
actual magnitude difference is only 0.42, which corresponds to a brightness
difference of about 50 percent.
The Moon becomes Last Quarter this afternoon at 1:03 p.m. EDT. If the sky is
quite clear, try to observe the Moon at the moment it turns Last Quarter, for no
reason other than to see if you can find it. The Moon will be 21 degrees (2 fists) up
in the west-northwest. A deep-blue sky will make the Moon easy to spot; the
contrast between moon and sky will be maximum. But if there's a haze, or thin
high level clouds that cast a milky veil over the sky, your task becomes more
difficult. Try first with unaided eye. Use binoculars if you are unsuccessful, but
once you locate the Moon, try again with naked eye.
The bright star Capella, part of Auriga (or-RYE-gah), the Charioteer, and a familiar
component of the "Winter Ellipse," just skims the northern horizon for mid-
northern latitudes. The zero-magnitude object rises during evening twilight in the
north-northeast. It is about 3 degrees (2 finger widths) up an hour after sunset.
First-magnitude Aldebaran, eye of the Bull, is the next bright object to rise. It
comes up about 3 hours after sunset in the east-northeast. An hour later Saturn
breaks the horizon between northeast and east-northeast. How soon after each of
these objects rises can you spot them?
Please send any comments, suggestions, or questions to
Thomas G. Ferguson:
fergus52@msu.edu
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