To the reader:
The Skywatcher's Diary for June 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 June issue, please send a long,
self-addressed stamped envelope to:
June 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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at
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ftp://www.pa.msu.edu/pub/swd/
Skywatcher's Diary: June 2003
Since late last year Saturn has been a nightly fixture near the horns of Taurus. As
time passed, the planet descended in the west and soon will disappear. Tonight
the thin crescent Moon provides one of the last easy chances to locate the planet
before it's lost in the twilight. An hour after sunset Luna sits 3 1/2 degrees (7
moon diameters) above, and slightly right of, zero-magnitude Saturn. At that
moment, the planet hovers only 3 degrees above the west-northwest horizon, so
you'll need an unobstructed view. You can try looking earlier, when Saturn is
higher, but use binoculars to spot the planet against the bright background sky.
The striking crescent Moon perches 9 degrees (a fist width) below the two bright
stars of Gemini during evening twilight. Pollux is the twin on the left and Castor
the one on the right. Can you verify that Pollux is slightly more luminous than his
brother? Tomorrow night the Moon appears in line with the twin stars, to their left.
The three objects are equally spaced, about 4 1/2 degrees apart. The later you
observe, the less exact the alignment becomes, since the Moon slides half a
degree (1 moon diameter) in its orbit per hour.
Mercury reaches greatest elongation today. The planet appears in the morning
dawn, 24 degrees from the sun. From our viewpoint, it's as though Mercury is
rounding the bend in its orbit. Although Mercury will be difficult to spot until it
brightens up, later in the month, bright Venus sits only 4 degrees to Mercury's left.
Forty minutes before sunrise, use the brighter planet to point your binoculars to
find the fainter sibling. At that time Venus perches 3 degrees above the east-
northeast.
This evening the crescent Moon stands 5 degrees (10 moon diameters or half a
fist) to the right of Jupiter. Near the end of twilight, look for the Beehive star cluster
5 degrees below and slightly right of the Moon. The swarm of faint stars is best
seen through binoculars. Regular observers may remember that Jupiter
approached within about a degree of the Beehive while it was ending its
retrograde (westward) motion in early April. The two objects won't venture that
close again until 2014.
Tonight the Moon lies between Jupiter and Leo, the Lion. Technically, Luna is
within the boundary of the lion, about where the imaginary cat's teeth might
appear. Perhaps that explains the crescent shape ‹ Leo has given the Moon a
playful nip. Notice Regulus, eight degrees (almost a fist) to the Moon's left. The
name Regulus means "little king," a name assigned by the renaissance
astronomer Copernicus. More often today we refer to it as the heart of Leo.
Tonight the Moon, a day away from First Quarter, lies in the body of Leo, king of
beasts. Regulus, the lion's heart, hangs 7 degrees (less than a fist) to the lower
right. A fainter star marks Denebola, Leo's tail, more than twice as far from the
Moon as Regulus, to the upper left. Denebola is a brilliant white star, hotter and
more luminous than our sun. From our distant vantage point, 36 light years away,
it shines at a rather average 2nd-magnitude.
The Moon officially turns First Quarter this afternoon at 4:28 p.m. EDT. After
nightfall, see if you can detect that the Moon is past First Quarter, that is, more
than half full. The large oval gray areas that you can pick out with unaided eye on
the upper left part of the Moon are lunar maria or "seas" ‹ actually ancient lava
lakes. The group of maria that flows from the upper right to lower left includes the
seas of Serenity (top right), Tranquility, Nectar, and Fertility. To the ancient
Chinese, the pattern formed by these dark areas looked like a leaping frog.
Toward the end of evening twilight, the great seasonal trio of bright stars known
as the Summer Triangle dominates the eastern sky. The group is not a single
constellation but rather 3 separate patterns that fill most of the space between
east and northeast and reach almost half way to overhead. The brightest of the
group is Vega, 40 degrees (4 fists) up in the east-northeast. Look for Deneb,
faintest of the threesome but still 1st magnitude, 25 degrees up in the northeast.
Altair sits not far above the eastern horizon, since it is the last of the triple treat to
rise.
The distinctly gibbous Moon sits near Spica tonight. Look for that star 6 degrees
(12 moon diameters) to Luna's lower left. Spica is the brightest star in Virgo. Its
name comes from Latin meaning "ear of wheat" which is pictured in the maiden's
left hand. The star we call Spica is actually two or more stars. The two major
components are hot blue-white stars that lie so close together that they orbit each
other every 4 days. Spica is sometimes associated with the "Diamond of Virgo," a
large pattern consisting of it, Arcturus, Denebola, and Cor Caroli in Canes
Venatici.
Pluto, the off again, on again planet, just reached opposition. The icy orb stands
opposite the sun in the sky. Opposition of a planet marks the midpoint of its best
visibility. The body is visible all night long and climbs highest above south in the
middle of the night. In Pluto's case, however, even its best visibility is poor. The
tiny outcast reaches only magnitude 13.8, brightening from 14.0. A telescope of at
least 8-inch aperture and a good finder chart is needed to separate the planet
from the multitude of other specks of light.
If you have an unobstructed view of the east-northeast horizon and don't mind
getting up early, consider following the dawn dance of Venus and Mercury over the
next week. The celestial ballet culminates on the morning of June 21 when
Mercury passes 0.4 degrees below Venus. A good time to look each morning is
40 minutes before sunrise. Tomorrow morning at that time Venus sits only 3
degrees off the horizon. Fainter Mercury perches 4 degrees (half a fist) to the right
and slightly above Venus.
Tonight the Moon rises in the southeast about 2 hours before sunset. Once the
sky darkens, notice the star Antares 8 degrees (16 moon diameters) below and
slightly left of the moon. The Moon inches closer to the star as the night
progresses. By tomorrow morning, as the Moon is setting, the gap between Moon
and star has shrunk to 5 degrees. Tomorrow night after twilight, you can observe
that the Moon has slid 9 degrees to the other side (left) of Antares.
Happy Triskaidekaphobia Day! Statistically, Friday the 13th occurs at least once
each year, but not more than three times. The likelihood of 1, 2, or 3 occurrences
is 43%, 43%, and 14%, respectively. Remember, our calendar system is a
human invention ‹ there's nothing special or supernatural about a particular
numbering scheme. Other cultural calendars keep track of the days of the year
differently. By and large the ancient superstition of bad luck on Friday the 13th has
been replaced by a more modern proclamation: TGIF.
The Moon turned Full this morning at 7:16 a.m. EDT. In colonial America the Full
Moon nearest the summer solstice was know as the Rose Moon, Strawberry
Moon, or Honey Moon, among others. Since the Full Moon appears opposite the
sun in the sky, the Moon's path across the sky is "opposite" the sun's. More
precisely, the Full Moon's trek tonight is similar to the sun's journey near the
winter solstice. Look for the Moon to remain relatively low as it travels from
southeast to southwest across the sky tonight.
Contrary to common expectation, the earliest sunrise occurs today for mid
northern latitudes, six days ahead of the longest day of the year ‹ the solstice.
Similarly, the latest sunset is postponed until June 28. This seeming incongruity
occurs because the Earth's orbit is elliptical rather than circular, and its rotation
axis is tilted relative to the orbit. If you yearn for a more thorough explanation, visit
this website: http://www.analemma.com.
To keep track of objects in the sky, astronomers employ a coordinate system
similar to the longitude and latitude that we use to mark locations on Earth. Right
Ascension designates a position east or west (like longitude) while declination
refers to north or south (like latitude). While the average stargazer would not
notice, some planetary astronomers might point out that today Saturn reaches its
greatest declination north of the celestial equator for the year ‹ 22.6 degrees.
The planet's Right Ascension is 6 hours 6 minutes 38 seconds.
If you haven't peeked at Venus and Mercury lately, the arrangement may catch you
off guard. Tomorrow morning, 40 minutes before sunrise, the pair sits 3 degrees
above the east-northeast horizon. One and eight-tenths degree separates them,
with brighter Venus to the left. The following morning (Thursday), Mercury pulls
obviously closer ‹ the spread is then 1.2 degrees. The next morning the pair is
0.7 degrees apart. Continue watching at least through Saturday morning. Use
binoculars.
The waning gibbous Moon slides under Mars tomorrow morning before dawn.
Look for the bright planet 2 1/2 degrees (5 moon diameters) to Luna's upper right.
Mars is beginning to show signs of the brilliance we anticipate this summer. An
hour before sunup Mars and the Moon are the two brightest objects in the sky.
The planet has brightened enough for even the casual sky watcher to detect an
orange hue.
Cassiopeia begins its slow ascent up the sky. Look for it low in the east-northeast
after dark. The distinctive shape is now oriented to portray a proper upright letter
"W." If you live in an urban environment, the city glow may overpower the
constellation when it is this low. To see it in this position, you will need to find a
darker observing site. Once it climbs higher, Cassiopeia is visible from all but the
most light-filled night skies.
Tomorrow morning Venus and Mercury will appear at minimum separation, only
0.4 degrees (just under a moon diameter) apart. Look 40 minutes before sunrise
very low in the east-northeast. Mercury (magnitude 0.8) hangs below and slightly
to the right of Venus (magnitude 3.9). You will want binoculars to initially pull
Mercury out of the twilight. Mercury continues to drop lower each morning, and
quickly becomes unobservable in the dawn glare.
The Moon reaches Last Quarter at 10:45 a.m. EDT. Coincidentally, the Summer
Solstice (northern hemisphere) also occurs today at 3:10 p.m. EDT. At that
moment, the sun reaches its farthest point north, relative to the constellations.
This event use to happen in the constellation of Cancer, which is the reason we
call the latitude where the sun appears overhead today the Tropic of Cancer. Now
the sun is actually among the stars of Gemini, the Twins.
After a grand evening appearance, Jupiter's reign will soon be over. Tonight, an
hour after sunset, look for the planet only 17 degrees (less than 2 fists) up in the
west. The star Regulus perches 13 degrees to Jupiter's upper left. Although
Jupiter's orbit carries it upward toward Regulus, the Earth's motion around the
sun dominates, causing the sun to appear to overtake Jupiter before it reaches
Regulus. By the end of next month the planet will succumb to the sun's glare.
The Big Dipper sits high in the north-northwestern sky in early evening. Some
night carefully examine the star at the bend of the Dipper's handle. If you have
average eyesight and a transparent sky, you should see two stars at that location,
one brighter than the other. The brighter 2nd-magnitude star is known as Mizar; its
4th-magnitude companion is Alcor. The two stars are separated by 1/5 degree, or
12' (minutes of arc). The human eye can theoretically separate two equally bright
points of light spaced 1' apart, although the practical limit may be closer to 3'.
Saturn is in conjunction with the sun today, which means it appears lined up with
Sol as seen from Earth. The planet's orbit carries it on the far side of the sun, so
today Saturn actually sits 839 million miles behind the sun. Although Saturn can
pass directly behind the sun, usually its orbit takes it above or below the Day Star.
Today the Ringed Planet swings a little less than a degree under the sun.
Canes Venatici (KAY-neez Veh-NAT-ih-sigh), the Hunting Dogs, nip at the heels of
the Great Bear, Ursa Major. The constellation is faint ‹ its brightest star is only 3rd
magnitude ‹ but not too difficult to find, thanks to the Big Dipper nearby and no
other stars as bright in the vicinity. Cor Caroli, that brightest star, sits 15 degrees
under the end of the Big Dipper's handle. That's about the same length as the
span of the handle. It lies roughly on a line between the Dipper's Bowl and the
bright star Arcturus
Cor Caroli, the major star in Canes Venatici, the Hunting Dogs, has nothing to do
with hunting or dogs. The name is Latin for "Heart of Charles," referring to King
Charles II of England. Edmund Halley, of comet fame and Astronomer Royal of
England, created the designation in 1725. It seems that astronomers, long ago
as today, were not immune from the realities of politics.
Early risers have been enjoying the sight of the thinning crescent Moon over the
last several mornings. This morning an hour before sunrise the star Aldebaran,
eye of Taurus, appears 6 degrees (12 moon diameters) to the lower right of Luna.
Although the Bull is usually thought of as a winter constellation, it begins
reappearing in the morning sky every year about now. Tomorrow morning the
Moon sits 13 degrees to the left of Aldebaran and 2 degrees above and slightly to
the left of Venus, but you'll need to look a bit later to catch the full view, about 40
minutes before sunrise.
Tonight the latest sunset of the year occurs for mid northern latitudes. Fortunately,
the sunset times do not change dramatically this time of year, so it's usually a
while before the average person becomes aware that we have started the down
turn toward winter. Furthermore, the temperature change lags the astronomical
seasons, so there's no need to panic and begin gathering nuts. Enjoy the lazy,
hazy, observing days and nights of summer.
The Moon turns New at 2:30 p.m. EDT. Luna will be much too young tonight ‹
only 7 hours old ‹ for any chance to catch a glimpse of it. Tomorrow night is a
different story. The hairline crescent appears 13 degrees (more than a fist) to the
left (south) of northwest and 3 degrees (6 moon diameters) to the lower left of
Pollux, brightest of the Gemini stars. Forty-five minutes after sunset Luna perches
only 3 degrees above the horizon. Binoculars may help you locate the Moon 15
minutes earlier and 3 degrees higher.
A line drawn southwestward from the end of the Big Dipper's handle, through Cor
Caroli in Canes Venatici, and extended its own length, ends up at the
constellation of Coma Berenices, the Hair of Berenice. The primary feature of this
exceedingly dim group is a spattering of faint stars spread over several degrees.
They have been described as sugar sprinkled on the sky, a depiction that works
best when observing from a dark location. The collection of stars belongs to a
star cluster containing a few dozen members at a distance of approximately 290
light years.
Please send any comments, suggestions, or questions to
Thomas G. Ferguson:
fergus52@msu.edu
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