To the reader:
The Skywatcher's Diary for August 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 August issue, please send a long,
self-addressed stamped envelope to:
August 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
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Skywatcher's Diary: August 2002
The Moon reaches Last Quarter this morning at 6:22 a.m. EDT. It is the first of two
occurrences for the phase in August. Phases repeat every 29 1/2 days, so when a
phase happens early enough in the month, it will recur near month's end.
Folklore labels the second of two full moons in a month as a "blue moon."
Following that lead, perhaps we should coin a term for the second incidence of
the other phases, starting with this month's Last Quarter. ("Blue Last Quarter" just
won't do). So your mission, should you decide to accept it, is to think of a name by
August 30, when the Moon is again Last Quarter.
Neptune, that mysterious blue orb near the edge of our solar system, passed
opposition last night, so our Earth is now between the sun and planet. What
significance is that to you? Not much, unless you want to catch a glimpse of the
distant gas giant. Opposition means Neptune is up all night, reaches its highest
point due south in the middle of the night, and shines at its brightest. That last
point is moot because Neptune is always relatively distant and faint (8th
magnitude). You will need a moderate telescope and a detailed finder chart to be
able to pick it out from the myriad of faint stars in Capricornus.
The crescent Moon welcomes early risers for the next several mornings. Look for
it in the east an hour or so before sunrise. This morning Luna stands 8 degrees
(almost a fist) to the upper right of Aldebaran, bright eye of Taurus. Tomorrow at
dawn look for it 8 degrees to the left of that star and 9 degrees to the upper right of
brighter Saturn. By Monday morning the Moon appears 4 degrees to the lower left
of the planet. The 3rd-magnitude star 1 degree (2 moon diameters) to Saturn's
right is the fainter "horn tip" of Taurus.
Venus continues to radiate its greetings each night at dusk. If you have been
watching the planet through the summer you are aware that it is dropping ever so
gradually and shifting a bit toward the south. The trend continues through this
month and next as Venus and Earth travel along their orbits. Later in August
Venus' phase will become more obvious in telescopes and eventually even in
binoculars. The planet now sets just under 2 hours after sunset.
Jupiter has begun to emerge in morning twilight, but it's still easy to miss. The
planet is only 12 degrees from the sun and rises about an hour before sunup.
Timing becomes critical -- wait long enough for Jupiter to climb above the horizon
but not so late that the bright sky masks your view. Forty-five minutes before
sunrise is a good bet. Look in the east-northeast. Take your binoculars.
Tomorrow morning the thin Moon is 18 degrees (2 fists) to the planet's upper
right. Wednesday morning the hairline crescent sits 5 degrees overtop Jupiter.
Earlier in the summer the Big Dipper hung nearly overhead toward the end of
dusk. Now the well-known star pattern has clearly descended. Look for it halfway
up in the northwest in the evening. Its handle leads to brilliant Arcturus, halfway up
in the west, and bright Spica, about 15 degrees above west-southwest. During
late autumn the Dipper scrapes the northern horizon, for observers at mid-
northern latitudes, making the shape difficult to find, as it mingles with the
landscape.
August and September mornings are the year's most favorable to see the
zodiacal light. Sunlight reflecting off small dust particles that float among the
planets' orbits creates a faint pyramid of light rising out of the eastern sky. The
zodiacal light is also known as "false dawn" because it is so often mistaken for
the beginning of morning twilight. The luminous glow is taller and narrower than
twilight, and the pyramid's axis is tilted toward the south. Look no later than 2
hours before sunrise, somewhat to the north of east. Pick a date without
moonlight and view from a dark site.
New Moon occurs at 3:15 p.m. EDT, so it won't be visible by nightfall. Tomorrow
night Luna will still be difficult for the casual observer. Early sighting of the Moon
was an important calendar keeping method in ancient times and still is for
marking the start of Islamic religious observances. Moons less than 24 hours
after New are difficult to view. The world record sighting without optical aid is 15
1/2 hours. If you are interested in further information on the factors that go into
young moon visibility, see the U.S. Naval Observatory's website:
http://aa.usno.navy.mil/faq/docs/islamic.html
You may be able to spot a hairline crescent Moon tonight, if several conditions are
met. You will need access to an observing site with a flat western horizon, and a
pair of binoculars. The weather also must cooperate and provide a transparent
sky. Arrive at the sight so that you are prepared to observe 30 minutes after
sunset. Venus should be visible then, about 12 degrees (a fist) above the horizon
and 15 degrees south of due west. The Moon will sit 30 degrees to the lower right
of Venus, 5 degrees off the horizon. Use binoculars to zero in on it. Mercury, also
tough to see, should be visible in the binoculars 4 degrees to the left of and
slightly below the Moon.
The Moon will be much easier tonight. It perches 16 degrees to the right and
slightly below Venus. Can you make out Mercury, 12 degrees to the lower right of
the Moon? Look 30 minutes after sunset to catch Mercury (use binoculars). Venus
and the Moon will be visible until they set, within a few minutes of each other, a
little less than 2 hours after sunset. Tomorrow night the Moon sits 5 degrees (10
moon diameters) to the upper right of Venus. Each night as the sky darkens, take
note of the earthshine, the dusky gray upper left portion of the Moon, where lunar
night is occurring.
Everyone's favorite summertime meteor shower reaches maximum over the next
two nights. The Perseids are reliable, producing one meteor per minute on the
average for an observer at a dark, clear site. The streaks of light are created when
the Earth collides with particles of dust left by Comet Swift-Tuttle. The meteors
should be especially active before dawn twilight tomorrow morning and anytime
after midnight the following night (actually, the wee hours of Tuesday morning).
The Moon even cooperates by setting early. Another endearing feature of the
Perseids is that they don't have a sharp peak of activity, so the view is still
worthwhile for several nights after the maximum.
The Moon sits 8 degrees (a fist) to the upper right of Spica, the brightest star in
Virgo. Brilliant Venus is 13 degrees to Luna's lower right. Take note of the relative
positions of Venus and Spica. Eighteen degrees currently separate the 2 objects.
Over the next 2 weeks Venus will approach Spica, passing within a degree of it on
August 31. Follow the progress every clear night, particularly the last week of the
month. As you watch over the extended period, the net appearance is that both
objects will drift slightly lower while drawing together. Thereafter Spica continues
downward and is lost in twilight by mid September while Venus hangs on.
Facing due north as darkness falls, you will see the Big Dipper 3 to 4 fist widths
on your left, and halfway up. Approximately 3 fists on the right, and a third of the
way up, resides Cassiopeia (cass-ee-oh-PEE-ya), a "W" shape about half the
size of the Big Dipper and slightly fainter. The constellation honors the ancient
queen of Ethiopia. The queen's notoriety comes from her antics in the Greek
legend of Andromeda. Cassiopeia and the Big Dipper straddle the North Star
(Polaris), a 2nd-magnitude star halfway up.
For those new to the hobby of stargazing, the North Star should be one you learn
to locate quickly. If the Big Dipper is visible, as it almost always is from mid
northern latitudes, use the old Boy Scout/ Girl Scout method. The 2 stars at the
end of the Big Dipper's bowl (the "Pointers") lead to the North Star. Extend a line
drawn between them one "dipper's length." The North Star's fame derives from its
chance placement almost exactly over the Earth's north pole. That puts the North
Star at the end of our planet's rotation axis. Consequently, as the Earth spins,
causing the heavens to whirl over our heads, the North Star remains fixed.
The Moon passes First Quarter this morning at 6:12 a.m. See if you can detect
that it is greater than half illuminated tonight. The 2nd-magnitude star 2 1/2
degrees (5 moon diameters) to the Moon's lower left is Delta in Scorpius, a hot,
blue-white star that marks the head of the scorpion. Brighter and redder Antares,
the heart of the celestial arachnid, lies 10 degrees to Luna's lower left. Be sure to
examine the Moon with binoculars or telescope. The craters along the terminator
(light/dark line) stand out nicely tonight.
The Moon hangs 6 degrees (half a fist) to the upper left of Antares tonight. Its
gibbous shape is now clearly evident. A small telescope reveals a prominent
mountain range, the Apennines, on the upper half of the surface near the
terminator. Near the top of the terminator, look for Plato, a conspicuous crater with
a dark, flat floor. Tomorrow night the Moon rests 18 degrees to the left of Antares.
It is then in the vicinity of the direction to the center of our Milky Way galaxy. That
spot, which has no naked-eye marker, is 4 degrees below and slightly right of the
Moon.
Saturn now rises more than 4 hours before the sun, so it is well up in the east by
daybreak. The ringed beauty in high enough before dawn to be an excellent
telescopic object -- relatively unhampered by the thick, unsteady air nearer the
horizon. That circumstance should be noted when planning any telescopic planet
observing session. Successful planet viewing depends on clear, steady
atmosphere. On any given night, generally the higher an object appears, the
better the view. With planets the atmospheric properties become critical, since
your objective is high magnification to be able to observe fine detail.
Tonight the Moon is near the "handle" of the "teapot" shape of Sagittarius. In the
early evening notice the 2nd-magnitude star Nunki two moon diameters to the
lower left. As the night progresses the Moon passes very close to the star for
observers in most the of U.S. (The minimum separation for Michigan skywatchers
occurs about 1 a.m. EDT.) Folks in western Canada and near the northwestern
U.S. boundary will see the Moon pass in front of the star, blocking it from view for
a period of time.
Uranus stands at opposition to the sun today, so Sol and the planet are on
opposite sides of the sky, from our vantage point. That means Uranus is above
the horizon when the sun isn't -- in other words all night long. Near opposition is
traditionally a time when amateur astronomers seek out the distant, faint planets.
They are up highest in the middle of the night and are at their peak brightnesses
for the year, although their luminosities vary little. Uranus reaches magnitude 5.7,
technically putting it in the category of a naked-eye object. If you feel up to the
challenge, try to spot it some clear, moonless night from a dark location. Do your
homework ahead of time. Study a detailed finder chart that marks the location of
Uranus within the constellation Capricornus. Presently that planet sits due south
a third of the way up at about 1:30 a.m. EDT. The Moon is in the vicinity August 21.
Use it for orientation but don't expect to see the planet that night. For viewing tips
see: http://skyandtelescope.com/observing/objects/planets/article_412_1.asp
If you haven't noticed Venus and Spica in the evening sky in a while, take a look.
An hour after sunset Venus is 6 degrees up near the west-southwest. First-
magnitude Spica is ten degrees (a fist) to the upper left. This week the separation
shrinks noticeably over a couple of days' time, and carries into next week. You
might also catch a glimpse of Mercury 2 fists to the lower right of Venus, but you'll
need to be out earlier. Forty minutes after sunset Mercury sits only 2 degrees
above the western horizon.
Vega, the brightest star in the Summer Triangle, passes just to the south of the
zenith (overhead) 2 hours after sunset. This gleaming white beauty is the 5th
brightest star in the sky, discounting the sun. The star is relatively close, only 25
light years away. That means the light showering you tonight left the star's surface
25 years ago. The star's proximity partially accounts for its brightness, but it is
intrinsically more luminous as well. If Vega were placed where our sun is, it
would shine 50 times brighter. Talk about global warming!
Full Moon tonight at 6:29 p.m. In simpler times the Full Moon of August was
dubbed the Green Corn Moon and the Grain Moon. Venus also reaches greatest
elongation today. It stretches 46 degrees to the east of the sun. The size of the
angle is only part of the visibility equation, though. Imagine the planet 46 degrees
directly over the sun, for example. In such a case Venus would set several hours
after sunset and be easy to view. Now visualize the planet 46 degrees to the
sun's left or right. In such a circumstance Venus would set near sunset and be
difficult to glimpse. The current situation is closer to the latter than former case,
so at this greatest elongation Venus is visible, but low in twilight.
Venus is a planet completely covered in bright white featureless clouds. The only
interest Venus holds for amateur astronomers with telescopes is its changing
shape and size. Fortunately Venus accomplishes both dramatically. Because its
orbit is inside the Earth's, we see Venus pass through all phases from crescent
to full. Futhermore, since it comes close to us, the planet's apparent size varies
significantly. In half an orbit, a telescope observer can watch Venus change from
a small round disk, almost dot, to a thin crescent 6 times larger in diameter.
Venus currently appears half full in a telescope. By early October the crescent will
be large enough to glimpse in binoculars
As darkness falls, Scorpius can be seen low on the southern horizon, stretched
out to the right of due south. If you are not familiar with this pattern, look first for the
heart, Antares, the bright ruddy star about 2 fists up in the south-southwest. The
body of the scorpion is formed by a string of stars trailing to the lower left from
Antares. If the night is free of summer haze and you have a flat view to the south,
you will be able to trace the path of stars down to just above the horizon, then to
the left, and as it swings back up in a wide arc that marks the animal's tail. Two
stars indicate the hook of the stinger.
Tonight the Moon rises just as twilight ends. Each successive night the Moon
rises later, providing longer periods of complete darkness without moonlight. The
time is ideal for enjoying the splendors of the summer Milky Way. Some night
soon, grab a pair of binoculars, a lounge chair, and something to keep you warm
as the air chills. Head to a spot where the sky is dark and open, get comfortable,
and simply gaze. Leisurely explore with unaided eyes and binoculars. Use a star
map if you feel the need, but don't be compelled. The goal is to absorb. Fill your
mind with the beauty.
At the end of evening twilight, the Milky Way rises out of the south, crosses just to
the east of overhead, and drops to the north. Two hours later it arches as high as
possible. As you gaze, notice the irregularities of the Milky Way, both along the
boundaries and within. The Milky Way seems to split in two through the Summer
Triangle and toward the southwest. It appears as though a goodly portion of the
Milky Way is missing. The feature is known as the Great Rift. It turns out to be
obscuring matter rather than the absence of Milky Way. The region is filled with
vast opaque clouds that hide the Milky Way stars beyond.
Venus and Spica, the brightest star in Virgo, are now 3 1/2 degrees apart (about
the width of 2 fingers). Look in the west-southwest 40 minutes after sunset. The
time is important. Venus should be easy to pick out if you don't have obstructions
in the critical direction. Spica will be a bit more difficult since it is more than 100
times fainter. Once you find Venus look to the upper left for the star. You may
recall that just last week 10 degrees separated the two objects. Set up an
observing schedule to watch every clear night 40 minutes after sunset, until the
end of this month. You'll be impressed by how quickly the scene changes from
night to night.
The Andromeda Galaxy is up at a decent viewing height by the end of evening
twilight. Look 30 degrees (3 fists) up between northeast and east-northeast. If you
are not familiar with the area, search with binoculars for a faint, small oval glow.
Move the binoculars slowly in an orderly pattern to scan the entire area. If you have
seen photographs of the immense spiral galaxy, don't be misled. The
Andromeda Galaxy appears featureless with binoculars and unaided eye. In fact it
is most unimpressive to the uninitiated. It isn't the image itself that draws people
to the binoculars and telescopes, but rather the knowledge behind the
appearance. Those who take the time to learn about what they see are often
captivated.
Are you continuing to check Venus and Spica each night? Forty minutes after
sunset look very low in the west-southwest. Tonight the pair is less than 2
degrees apart. You may be able to glimpse Mercury before it sets, 18 degrees (2
fists) to the lower right of Venus and just above the horizon. Tomorrow morning
the almost-Last-Quarter Moon shows prominently at dawn. It sits among the stars
of Taurus. Aldebaran is the bright star 11 degrees to Luna's lower left. The
Pleiades star cluster perches 5 degrees (10 moon diameters) above the Moon.
The second Last Quarter Moon of this month occurs at 10:31 p.m. Since it doesn't
rise until around midnight, you'll have to take our word that there's nothing special
about the moment. Tomorrow morning look for the just-past-Last-Quarter Moon
high in the southeast at dawn. Aldebaran is the star 5 degrees (10 moon
diameters) to Luna's lower right. Saturn sits 16 degrees (3 times the moon-
Aldebaran distance) to the Moon's lower left. The following morning (Sunday) the
Moon jumps to 3 degrees above the Ringed Planet. Jupiter is the bright planet 18
degrees up in the east an hour before sunrise. The Moon reaches its vicinity the
morning of September 4th.
Venus and Spica are closest tonight -- only 0.9 degrees separate them. The
optimum time to observe is 40 minutes after sunset, but you may well find them
earlier. At sunset or before, you should be able to locate Venus in binoculars by
carefully searching the west-southwest. Venus sits 14 degrees (fist and a half)
above the horizon at sunset. Spica will be in the binoculars' field of view, to the
upper right of Venus but may not be visible for a while. How soon are you able to
see Venus and Spica with binoculars? When are they visible with your unaided
eye?
Please send any comments, suggestions, or questions to
Thomas G. Ferguson:
fergus52@msu.edu
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