To the reader:
The Skywatcher's Diary for July 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 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
http://www.pa.msu.edu/abrams/SkyWatchersDiary/Archives.html
ftp://www.pa.msu.edu/pub/swd/
Skywatcher's Diary: July 2004
The Moon makes its second closest approach to Earth for the year around 11
p.m. tonight. It is only 125 miles farther away than last month's nearest perigee.
About eight hours later the Moon turns Full. The coincidence of close approach
and Full Moon will produce relatively high tides in areas of the world affected by
the ebb and flow. As well, the Moon will appear larger, technically speaking. In
practice, the Moon's apparent size involves ample subjectivity.
The Moon is exactly Full at 7:09 a.m. this morning. Its designation in colonial
times was Thunder Moon or Hay Moon. Because the Full Moon occurs so early in
July, there's enough time left in the month for an encore performance. The interval
between repeating phases is 29 1/2 days. Today also marks the midpoint of the
year. Beginning now, 2004 is all downhill.
Mercury sits low in evening twilight all month. Look for it tonight 3 degrees above
the west-northwestern horizon 45 minutes after sunset. See if you can pick out the
bright star Pollux 7 degrees (less than a fist width) to the right of Mercury and faint
Mars the same distance to the upper left of the planet. You will probably need
binoculars to pluck these objects from the bright twilight. Mercury is brightest at
the start of July and fades throughout the month, so look sooner rather than later.
In keeping with the Red, White, and Blue theme of the day, let's look for bright
stars that radiate these colors. The epitome of a red summer star is Antares,
heart of Scorpius, and due south near the end of evening twilight. For white, use
Vega, brightest of the Summer Triangle, although any of the Triangle stars will do.
Locate Vega two-thirds of the way up in the east. The best we can do for blue is
blue-white Spica, of Virgo, a little more than two fists above the southwest horizon.
Venus appears about a degree from the star Aldebaran, currently in the morning
sky. An hour before sunup, look for the pair 10 degrees (a fist) above the horizon
and slightly north of due east. The brighter planet is to the upper left of the star.
Continue watching on clear mornings as the two objects climb higher out of
twilight but also separate. Note the crescent shape of Venus in binoculars or
telescope.
Earth just passed aphelion in its orbit. That's astronomer lingo for greatest
distance from the sun. In round numbers, ninety-four and a half million miles now
separate us from our parent star. For those who may think our seasonal
temperature changes are due to the sun's relative distance, how do you reconcile
that we are farthest from the sun during the hottest part of the year?
Mars, only 2nd magnitude, appears 3 degrees (about the width of two fingers) to
the upper right of brighter Mercury low in the evening sky. Over the next several
evenings the planet pair draws ever nearer, closing to within a mere 0.2 degrees
of one another on the evening of the 10th. Observe the two every clear evening to
witness the dramatic change. Look 45 minutes after sunset, about 3 degrees
above the west-northwest horizon.
Jupiter is the planetary ruler of the evening sky, but not for much longer. The giant
planet now sets 3 hours after sunset. By the end of the month, that interlude
reduces to 1 1/2 hours. Tonight, with the planet only 20 degrees up an hour after
sunset, it's already becoming difficult to obtain a good telescopic view. Savor the
observing opportunities that remain. Jupiter won't return to the evening sky until
early next year.
The Moon reached Last Quarter early this morning, at 3:34 a.m. EDT. It rises a
couple hours before that time, about 4 hours after sunset, near the middle of the
night. The Moon is also readily visible during early daylight hours tomorrow. Look
for it due south and more than halfway up in the sky an hour after sunrise, or
about the time of that morning commute. During the lunch break you may still
catch a peek, if you have an unobstructed view to the west.
You may still have a chance to see fleeting Mars, with help from Mercury. The two
planets sit within two-tenths of a degree tonight. Mars is at its faintest and sinking
in the west. Without brighter Mercury to show the way, the Red Planet would surely
be lost in the twilight haze. Look for the pair 45 minutes after sunset 5 degrees
(half a fist) above the west-northwest. Mars hangs directly below Mercury.
The magnificent summer constellation of Scorpius now straddles the southern
horizon at nightfall. Gleaming Antares is the luminary and heart of the scorpion.
To that star's upper right lies the head region, and to the lower left flow the body
and tail. Pay particular note to the two stars at the tip of the tail, the stinger, which
curves upward. The Navajo Indians view that pair of stars as part of a rabbit track
created by the rabbit's hind legs. The two stars immediately below the pair
represent the tracks from the forelegs.
At dawn tomorrow, the waning crescent Moon perches between two star clusters
-- the Pleiades (above and right) and Hyades (below). Seasoned observers will
recognize the Hyades also as the "face" of Taurus, the Bull. The brilliant object 9
degrees (a fist) directly below the Moon is Venus. Notice, also, the bright star 3
degrees to the planet's upper right. That's Aldebaran, the eye of Taurus.
Venus is now at greatest brilliancy, and it is something to behold. Too bad most
people will miss the show because the planet performs at such an inconveniently
early hour. Tomorrow morning look for Venus in the east-northeast 10 degrees (a
fist width) to the right of the Moon. If you enjoy a leisurely morning schedule, try
following the Moon and Venus through sunrise. How long beyond sunup can you
locate the planet?
Tomorrow morning is the last easy opportunity to observe the thin crescent Moon
before it fades into New. An hour before sunrise Luna sits 9 degrees above the
horizon and slightly north (left) of east-northeast. If you crave more of a challenge,
the following morning (Friday, the 16th), 45 minutes before sunrise, the hairline
crescent rests only 3 degrees up and also to the north of east-northeast. Its age,
then, is about 26 hours before New.
The direction toward the center of our Milky Way lies due south and highest (about
20 degrees up) at the end of evening twilight this time of year. With the Moon out
of the way, take the opportunity to inspect this part of the sky from a dark location.
It is rich in "star clouds," dense clumps of stars. Leisurely scan the region with
unaided eye and binoculars. Take along a lounge chair that can support your
neck and a blanket to stifle a potential chill.
To most observers, Cassiopeia is the second most recognizable constellation in
the northern sky. Some even put it ahead of the Big Dipper. Look for the familiar
"W" shape, not yet halfway up in the northeast as darkness descends.
Cassiopeia is similar in brightness to the Dipper but shorter in length. The
rightmost star of the "W" pattern is known as Caph, an Arabic name that means
"stained hand," which in ancient times referred to the entire pattern.
New Moon occurs at 7:24 a.m. EDT. Observers in Hawaii and farther west may
have a chance to catch a glimpse of a very young Moon tonight, but those of us in
the continental U.S. (except, perhaps, the extreme Southwest) must wait another
24 hours. Tomorrow night, look 45 minutes after sunset in the west-northwest.
The Moon will perch 4 degrees (half a fist) above the horizon. Mercury sits 9
degrees to Luna's left. The real test is to find faint Mars 3 degrees to the Moon's
lower left and 6 degrees to Mercury's lower right.
Caph, the star farthest right (east) in Cassiopeia's "W" shape, lies almost exactly
on the zero point of the sky's coordinate system -- the astronomical prime
meridian, so to speak. By comparing the star's position to Polaris, the North Star,
a serious observer can estimate the sidereal (star) time and, thereby, the
orientation of the sky for that particular moment.
Tonight the young crescent Moon is still rather low and slightly north of west. If you
look early enough, you may be able to detect the nearly equal-sided triangle
created by the Moon, Mercury (5 degrees below Luna) and Regulus, the 1st-
magnitude star in Leo that's 5 degrees to the Moon's lower left. Forty-five minutes
to an hour after sunset is the best time to look. The bright "star" 20 degrees (2
fists) to the upper left of the crescent is Jupiter.
Where were you 35 years ago today? If you were grade school age or older, you
probably were close to a television or radio at 4:17 p.m. EDT hoping to hear that
Neil Armstrong and Buzz Aldrin had become the first humans to safely land on the
Moon's surface. Three and a half decades later, some individuals insist that the
landing never happened. How utterly silly, and sad.
Tonight the crescent Moon and Jupiter make a nice pair. Their separation
matches the distance between the Pointer Stars, the two stars in the end of the
Big Dipper's bowl. Speaking of the Pointers, Comet NEAT is still in the sky and
passes between the Pointer Stars tonight. By now the comet is quite faint, but
should be visible in good binoculars from a dark location. Look for a dim out-of-
focus "star" positioned slightly closer to the lower Pointer Star.
Venus now rises almost 3 hours ahead of the sun, so it dominates the predawn
scene. The planet is still at its brightest. Venus is also close enough to Earth to
show a crescent shape in binoculars and telescopes. The crescent has widened
noticeably since the beginning of the month, about doubling in size. If you have
the time to monitor Venus for 45 minutes or an hour, find it in twilight, say 30
minutes before sunrise, and continue following it after the sun is up for as long as
you can.
Look for Jupiter's moons with your telescope tonight. Observe as soon after
sunset as you can, since Jupiter will then be higher and the eyepiece image
appears sharper. Three of the planet's four major moons are visible, two on one
side of the disk and one on the other. The single moon is Europa. Opposite
Europa, look for Ganymede, closer to Jupiter, and Callisto farther out. A fourth
moon, Io, emerges out of Jupiter's shadow only 30 minutes before the planet
sets.
The Moon turns First Quarter at 11:37 p.m. EDT. Also tonight Mercury passes
nearest to the bright star Regulus. The separation is a little more than a degree (2
moon diameters). Look 45 minutes after sunset, 8 degrees (about a fist) to the
right (north) of due west and 8 degrees above the horizon. Mercury is the brighter
object; Regulus is above and slightly right. Since the planet and star appear in
bright twilight, bring binoculars to locate them.
The constellation Sagittarius, a favorite of summertime sky watchers, sits low at
nightfall and just to the left (east) of due south. Experienced observers usually
think of it as the "teapot" because the outline traced by its brighter stars bears a
resemblance to that piece of tableware. Sagittarius hosts a number of well known
"deep sky objects" within reach of small telescopes and binoculars. Look before
the middle of next week when the bright Moon arrives in that area.
While known to most observers as the "teapot," the classical representation for
Sagittarius is the Archer. The names of several of the constellation's stars allude
to this ancient centaur figure armed with bow and arrow. The star at the top of the
"lid" is Kaus Borealis, which literally means "northern (part of) bow." At the bottom
of the spout is Kaus Australis, or "southern bow." Between the two, resides Kaus
Meridionalis, "middle bow." And the spout's tip, Nasl or Nash, translates as "the
point" (of the arrow).
Mercury "rounded the bend" in its orbit late last night. Astronomers call this event
a "greatest elongation." The angular distance between Mercury and the sun is at a
relative maximum -- it's 27 degrees at this elongation. Mercury was easier to
locate earlier in the month, but the planet is still visible low in the western sky 16
degrees to the lower right of Jupiter. Look 45 minutes after sunset. Also tonight
notice the star Antares, heart of Scorpius, 5 degrees (10 moon diameters) to the
Moon's right.
The Moon passes through the "teapot" shape of Sagittarius over the next two
nights. Tonight Luna is in line with the leading edge of the spout. Third-magnitude
Nasl (or Nash) sits 3 degrees (6 moon diameters) to the Moon's lower left, and
2nd-magnitude Kaus Australis is 6 degrees to Nasl's lower left. Tomorrow night
Luna jumps to the teapot's handle. Third-magnitude Tau, the handle's bottom left
corner, is then 1 moon diameter to Luna's upper left.
Saturn emerges out of the glow of dawn this week. An hour before sunrise the
planet sits only 3 degrees (about 2 finger widths) above the east-northeast
horizon. Brilliant Venus is 27 degrees (almost 3 fists) to Saturn's upper right. The
Gemini Twins, Pollux and Castor, are about a fist to the planet's upper left. Rising
about 4 minutes earlier each day, Saturn will soon pull free of the morning glow.
On what morning will you first see it?
Arcturus, the brilliant star sitting about halfway up in the west at nightfall, resides
in the constellation of Bootes (boh OH teez), the Herdsman. When searching for
Bootes this time of year, most sky watchers look for the kite shape pattern of stars
that flows to the upper right of Arcturus. The constellation name "Bootes" is very
old -- its origin is lost in the dim past. Other common meanings associated with
the name include the Ploughman and the Bear Driver, the latter appellation
alluding to the proximity of Bootes to Ursa Major, the Great Bear.
The Moon turns Full this afternoon at 2:05 p.m. EDT. It's the second time this
month that the Moon has reached full phase. In popular usage, the second full
moon is called a "Blue Moon," although historically, other definitions have been
used. Astronomically speaking, there's nothing special about two full moons
occurring in the same month. It's simply a by-product of the way we define our
calendar year.
Please send any comments, suggestions, or questions to
Thomas G. Ferguson:
fergus52@msu.edu
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