To the reader:
The Skywatcher's Diary for July 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 July issue, please send a long,
self-addressed stamped envelope to:
July 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: July 2003
A striking two-day old Moon greets observers this evening. The fragile crescent
sets only 2 hours after the sun, so don't expect to find it after twilight. An hour after
sunset the Moon perches 11 degrees (a fist width) above the western horizon and
12 degrees to the lower right of brilliant Jupiter. Tomorrow evening the slightly
larger crescent slides above Jupiter. Four degrees (8 moon diameters) will
separate the two bodies.
It's "over-the-hump" day, the 183rd rotation of planet Earth during 2003. The exact
midpoint of the year occurs today at 1 p.m. local daylight time. Although there's no
astronomical reason for noting this date, humans often find such divisions of time
helpful in organizing activities and assessing progress. For better or worse, the
year is half over. It's time to enjoy the downhill ride.
The Moon spends the next two nights within the constellation of Leo, the Lion. The
star 5 degrees (half a fist or 10 moon diameters) below Luna is Regulus, heart of
Leo. The semi-circle of fainter stars to the Moon's right represents the lion's
head. The brightest star of that group is 2nd-magnitude Gamma or Algieba, 6
degrees to Luna's upper right. To be certain you are looking at Algieba, try to spot
the 5th-magnitude star less than a moon's width to Algieba's lower left. Binoculars
will help.
Coinciding with the country's birthday, Earth reaches aphelion, its farthest point
from the sun. While our Independence Day celebration is locked on the same
calendar date, aphelion can vary up to a couple of days either side of this date.
Today we sit 94,510,779 miles away from the sun. That's 3,105,431 miles or 3.4
% farther than last January 4, when we stood closest to Sol. Don't expect today's
more distant sun to provide any relief from summertime temperatures, however.
The Earth's tilted axis is the primary cause of our seasonal temperature shifts.
Mercury travels in back of the sun today, a configuration known as "superior
conjunction" to astronomers. Because the planet's orbit is tilted 7 degrees to the
Earth's orbital plane, Mercury usually doesn't pass directly behind the sun but
rather above or below it. Today Mercury invisibly slides 1 1/2 degrees north of Sol.
Mercury hereafter passes into the evening sky and will become visible near
Jupiter after mid month.
The Moon reaches First Quarter at 10:32 p.m. EDT, so you have the opportunity to
observe it at that exact moment. If you consider doing this, be aware that you have
no life and need to develop some other interests. Recall that the First Quarter
Moon, by definition, is 90 degrees away from the sun. It, therefore, follows the sun
across the sky by about a quarter day. When, then, does the Moon rise today?
Approximately 1/4 day after the sun, or around midday.
Venus and Saturn pass within a degree of each other tomorrow before sunup.
Venus has been ever so slowly disappearing into the morning twilight while
Saturn's just emerging from the glow. To catch sight of the duo, a flat,
unobstructed east-northeast horizon is a must. Look 40 to 30 minutes before
sunrise. Use binoculars to separate the planets from the sky glare. Fainter Saturn
will appear 0.8 degrees to Venus' lower right.
Gleaming Mars reaches its highest point (34 degrees) due south as the glow of
dawn begins. For those observers who are night owls rather than morning larks,
Mars now rises around midnight local time, so you can catch it in the east-
southeast before turning in. The planet is conspicuously bright, now more brilliant
than Sirius, the brightest star. Radiating at magnitude Ð1.6, Mars is still a pale
image of what it will become in late August when the Red Planet reaches
magnitude Ð2.9.
Tonight the gibbous Moon crosses the boundary from the constellation of Libra,
the Scales, into Scorpius. The bright star 13 degrees (more than a fist) to Luna's
lower left is Antares, heart of the scorpion. The Moon travels about 13 degrees in
its orbit per 24-hour period. Tomorrow night observe that the Moon appears close
to Antares, only 3 degrees to the star's upper left. The following night Luna travels
another 13 degrees, ending up near the tail of Scorpius.
Tomorrow night try to note the Moon's position relative to the starfield. Although no
stars brighter than 2nd magnitude are in the vicinity, with some persistence you
should be able to trace the tail of the scorpion and the spout of the teapot to the
Moon's lower right and lower left, respectively. The purpose of this exercise is to
roughly locate the direction toward the center of our Milky Way Galaxy. In 4 or 5
days, once the Moon has left the region, come back to it and explore with
binoculars.
If you observed Venus and Saturn when they were closest on July 8th, be sure to
take another look tomorrow morning. Comparing the two views will leave no
doubt that Venus is leaving the morning sky while Saturn is entering. Forty
minutes before sunrise tomorrow, the two planets stand more than 4 degrees
apart, with Saturn to the upper right. Look low between east-northeast and
northeast. Use binoculars. If you don't see Venus immediately, keep looking. Give
it more time to climb above the horizon.
Tonight the almost Full Moon appears among the stars of Sagittarius. Although
the constellation name refers to a centaur archer figure, most observers look for a
teapot shape. Near the end of evening twilight the Moon sits at the top end of the
"handle." Try to pick out 2nd and 3rd-magnitude stars to the left and upper right of
the Moon, respectively. They lie between 2 and 3 moon diameters away. Because
of the bright moonlight, you may need binoculars to initially find the stars.
The Moon turns Full at 3:21 p.m. EDT. After dark, can you tell that the Moon is
more than full? Use binoculars or telescope to examine the upper right limb for
indications the Moon is slightly "out of round." In colonial America the Full Moon of
July was known as the Thunder Moon or Hay Moon. The path that the Moon takes
across the sky tonight is close to the sun's trek across the daytime sky 6 months
earlier. Like the sun in January, tonight's Moon follows a low arc from roughly
southeast to southwest.
This time of year the magnificent summer constellation Scorpius reaches its
highest point in the south near the end of evening twilight. A graceful curve of
stars stretches from the scorpion's head, on the right, through its bright heart,
Antares, and on to the tip of its tail. The flowing pattern seems to relax the eye as
your vision wanders down that string of stars. Seek out Scorpius some night
before the Moon rises so you can better examine its details. What a pity for
northern observers that Scorpius doesn't climb higher above the horizon. The
summer haze that frequently lingers near the horizon can obscure all but the
brightest part of the scorpion.
If you haven't been paying attention to the gradual westward march of the sky from
night to night, you may have lost track of Spica, the 1st-magnitude star in Virgo.
Locate it one quarter of the way up in the southwest an hour after sunset. With the
lengthy twilight this time of year, you might have difficulty recognizing the star at
first. Recall the old rule, "Follow the arc to Arcturus and speed on to Spica." That
is, use the Big Dipper's handle to draw an imaginary curve through Arcturus and
then Spica.
The Moon rises more than 2 hours after sunset, not too long before midnight.
Once the Moon climbs high enough, notice brilliant Mars 2 degrees (4 moon
diameters) to Luna's left. As the night proceeds, the Moon edges ever closer to
the planet, passing spectacularly close in early dawn tomorrow (Eastern time
zone). Observers in extreme southeastern Florida can watch the Moon pass in
front of (occult) Mars.
The glowing arc of the Milky Way Galaxy passes directly overhead about 3 hours
before sunrise. Some early morning, take in the wondrous vista of billowing star
clouds and dark dust lanes. Scan the length of the galaxy with binoculars,
pausing at sights that catch your eye. If the early morning hour seems an unlikely
time for you to be observing, just wait. The Milky Way crosses overhead 2 hours
earlier per month, so eventually a time will arrive that's more to your liking.
Pop Quiz: What faint constellation is passing overhead near the end of evening
twilight. It lies between the bright stars Arcturus, in the southwest, and Vega, in
the east, but closer to Vega. It's a name most everyone will recognize, even if they
no nothing of the constellation. Stop and think about it or go outside and observe
before reading further. The constellation is named after a hero of Greek
mythology. Hercules is the answer.
Jupiter is not long for the evening sky. Have you seen it recently? It sets in the
west-northwest a little more than an hour after sunset. Before disappearing,
Jupiter is due to have one last fling with Mercury. Look not later than 40 minutes
after sunset. Jupiter glistens at magnitude Ð1.7. Mercury is a magnitude fainter
and 9 degrees (a fist width) to Jupiter's lower right. Watch the changing
configuration of these two planets each night after sunset. Their closest approach
occurs on the 25th.
The Moon reaches Last Quarter tomorrow morning at 3:01 a.m. EDT. Two weeks
ago we mentioned that the First Quarter Moon trails the sun across the sky by
approximately one-quarter day. Similarly, the Last Quarter Moon leads the sun by
that amount. About what time should tomorrow's Moon set, therefore? Roughly
midday is the answer. By the way, noon (12 o'clock) and midday (the middle of the
day, the sun is due south) are not the same thing. Midday depends on location as
well as other factors. For example, in mid Michigan, midday currently occurs at
1:44 p.m. EDT.
The bright star 17 degrees (almost 2 fists) up in the eastern morning sky 1 1/2
hours before sunrise is Aldebaran, yellow-orange eye of Taurus, the Bull. If you
recognize that constellation, you probably know it as a wintertime pattern
associated with Orion. The appearance of Aldebaran before dawn tells us that the
winter stars are now emerging as morning stars. Night by night they will slowly
drift across the sky, eventually to become evening stars again this winter.
The bright star in the northeast during dawn is Capella, in the constellation
Auriga, the Charioteer. Celestial objects that never rise and set are called
circumpolar because they endlessly pivot around the North Celestial Pole. The
latitude of the observer on Earth determines if an object is circumpolar. Capella,
for example, becomes circumpolar near latitude 44 degrees north and higher.
(That's about the latitude of Michigan's Houghton Lake.) Anyone positioned at 44
degrees north should see Capella just skim the northern horizon about 1 hour
and 45 minutes after sunset.
The distance between Earth and Mars continues to shrink, and today a milestone
is reached. The Red Planet now sits less than 42 million miles from us in the
direction of the constellation Aquarius. That's the closest we've been since 1988.
Consequently, Mars now appears largest since that year. The planet's apparent
diameter is 20.7 seconds of arc and growing. When closest in late August, Mars
reaches 25.1 seconds of arc.
Look for Jupiter and Mercury tonight, shortly after sunset. The two planets appear
1.4 degrees (3 moon diameters) apart. Forty minutes after sundown they sit only
3 degrees off the west-northwest horizon. Mercury, the fainter of the two, appears
on the right and slightly lower than Jupiter. Over the next several nights Mercury
slides to the upper left, above Jupiter. Compare tonight's view to tomorrow night,
when less than half a degree separates the planets.
Saturn now rises 2 hours before sunup, so the ringed beauty is becoming easier
to pick out from the east-northeast morning twilight. Today the planet reaches its
nearest point to the sun (perihelion), 839 million miles. That's about 50 million
miles closer than average. The event is noteworthy for the fact that it happens only
once each Saturnian orbit, so it will be 2033 before you'll once again bear
witness. The Moon is near Saturn the next two mornings.
Take another look at Jupiter and Mercury this evening, low in the west-northwest
40 minutes after sunset. Mercury has changed sides. It now sits 1.4 degrees to
the upper left of Venus. Regulus, the brightest star in Leo but fainter than Mercury,
appears 5 degrees to that planet's upper left. As nights proceed, Jupiter sinks
lower and Mercury climbs toward Regulus.
Tomorrow morning the very old (thin) crescent Moon appears only 3 degrees (6
moon diameters) above the east-northeast horizon 40 minutes before sunrise.
The Gemini stars, Pollux and Castor, align with the Moon. Pollux lies about 3
degrees to Luna's upper left. Castor perches another 5 degrees beyond that.
Here's a chance to add a morning crescent that's within 24 hours of New to your
collection. New Moon occurs in about 21 hours. Use binoculars.
The south Delta Aquarid meteor shower reaches its peak in a moonless sky
tomorrow morning before daybreak. Although it's considered a major shower, the
event is one of the lesser outbursts for that category. At maximum, expect to see
not more than one meteor every 5 minutes on the average. The peak is broad,
however, so the display should not dip much below maximum for several days.
The Moon reaches New phase at 2:53 a.m. EDT this morning. Tonight observers
in Michigan have a crack at a less than 19-hour-old Moon. That's only about 3
hours older than the record naked-eye sighting. Thirty minutes after sunset the
Moon sits about 2 degrees above the west-northwest horizon. A little preplanning
will make you more likely to succeed. Go out just before sunset and watch
carefully as the sun disappears below the horizon. Memorize the location by
sighting along a natural feature or post. Thirty minutes after sunset the Moon
appears 2 degrees above that spot.
The Moon, two planets, and a star create an interesting grouping tonight just after
sundown. Unfortunately, all of the objects are quite low, so the casual observer
may not see them. The crescent Moon is easiest. Forty minutes after sunset it
hangs 6 degrees above the west-northwest. Jupiter sits on the horizon, 9 degrees
to Luna's lower right. Mercury and Regulus, less than a degree apart, are 4
degrees to the Moon's lower left.
An exquisite Moon shines in the west after sunset. For attractive background sky
coloring, look about 30 minutes after sunset. Mars has just begun its retrograde,
an apparent reversal of its usual eastward motion against the more distant starry
background. Mars won't return to "normal" motion until September 29th. In
between, near the end of August, the Red Planet passes closer to Earth than it
has for tens of thousands of years. Stay tuned.
Please send any comments, suggestions, or questions to
Thomas G. Ferguson:
fergus52@msu.edu
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