To the reader:
The Skywatcher's Diary for June 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 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
archives
at
http://www.pa.msu.edu/abrams/SkyWatchersDiary/Archives.html
ftp://www.pa.msu.edu/pub/swd/
Skywatcher's Diary: June 2004
Venus is fast disappearing from the evening sky. On what date will you last see
it? Look 15 minutes after sunset in the west-northwest. Tonight at that time, the
planet sits 5 degrees (half a fist width) above the horizon. Use binoculars to
initially locate Venus. The planet's thin crescent shape should become apparent
in the binoculars. If you don't see it right away, keep looking as the sky darkens.
Venus sets an hour after sunset.
The Moon turns Full at 20 minutes past midnight tonight, officially tomorrow
morning. About 9 hours later, Luna makes its closest approach to Earth for the
year. The interplay of these two events creates the potential for the highest tides of
2004. It also produces the largest appearing Full Moon. There's certainly
subjectivity in how big the Moon seems, however. To most people, any rising or
setting Full Moon appears huge. The star 3 degrees (6 moon diameters) to
Luna's upper right is Antares.
Comet LINEAR begins its evening appearance for northern latitudes. Use
binoculars to search in the west-southwest 11/2 hours after sunset for a faint fuzzy
spot. The comet remains in the vicinity of the 2nd-magnitude star Alphard, the
brightest object low in that direction. Tonight LINEAR is 6 degrees (half a fist)
below Alphard. On June 6th the comet passes 2 degrees to the left of the star.
An extraordinarily rare transit of Venus takes place in four days. As the planet's
orbit carries it between the Earth and the sun, all three bodies align nearly
perfectly. For a few hours, observers on Earth can watch Venus move across the
sun's face. The planet's silhouette, projected onto the much larger and brighter
disk of the sun, shows up as a tiny black dot. Although you may be able to see the
event without the magnification of a telescope, proper solar filtration is absolutely
necessary to avoid permanent eye damage.
Europe, the Middle East, Africa, and Asia are most favorably placed for the transit,
but the eastern U.S. (including Michigan) can catch the end of the show just after
sunrise on June 8. If you don't have equipment to safely view the sun, find a local
observing session to join. Check with planetariums, science museums,
observatories, and astronomy clubs in your area and share in this rare event.
A transit of Venus last occurred in 1882, so it's safe to say that no living human
has ever witnessed the phenomenon. Venus transits occur in pairs eight years
apart. The pairs are separated by more than 100 years. This year's transit is the
first of two. The next one occurs on June 5-6, 2012. At least part of that transit will
be visible from everywhere in the U.S.
For eastern North America, the transit of Venus is in progress tomorrow morning
at sunrise. As the sun rises, the silhouette of Venus appears near the lower right
edge of the disk. The intensely black dot slides to the upper right, touching the
sun's limb at 7:05 a.m. EDT, and then slips off Sol's face entirely by 7:25 a.m.
(Michigan times). Be absolutely certain that you have safe filtering to view the sun.
Don't risk permanent eye damage.
On the northern shore of Tahiti, a small promontory of land is known as "Point
Venus." It marks the location from which Capt. James Cook and his crew
observed the transit of Venus in 1769. Many scientific expeditions were mounted
in that year to record the transit from far off lands. By combining the worldwide
observations, scientists were able to calculate the distance between Earth and
sun to within 1 percent, a triumph of 18th century science and human fortitude.
The Moon attains Last Quarter phase this afternoon at 4:02 p.m. EDT. It rises
significantly after midnight and reaches due south after sunrise, which means
Luna is visible for several hours during morning daylight. If you catch the moon in
darkness, notice that it sits 3 or 4 fists (30 or 40 degrees) to the lower right of the
Great Square of Pegasus.
Arcturus, the magnificent orange tinted star, crosses the meridian (due south)
about an hour after sunset. Look more than two-thirds of the way up for the
brightest object in that part of the sky. Arcturus is moving through space at a
different speed than other stars in the sun's neighborhood. One intriguing theory
that accounts for the difference suggests that Arcturus is from a small galaxy that
fused with our Milky Way five or more billion years ago.
Pluto, that off again, on again planet, is now visible all night among the stars of
the constellation Serpens, the Serpent. The tiny resident of the outer solar system
is only 14th magnitude and requires at least an 8-inch aperture telescope and a
detailed finder chart to spot. Incidentally, astronomers consider the argument over
Pluto's planetary status to be unproductive. What's important is determining in
what ways Pluto is like other celestial bodies and in what ways it's different.
Comet NEAT is still faintly visible in binoculars. The comet currently resides in the
constellation of Ursa Major. Imagine a line passing diagonally through the bowl of
the Big Dipper, beginning from where the handle connects and drawn downward,
then extend the line 10 degrees (a fist) beyond the bowl. Search in that vicinity for
a faint "out-of-focus star." The comet remains in Ursa Major for most of the
summer. It passes through the Dipper's bowl in early August.
The Moon now appears in the morning sky just ahead of sunrise. The waning
crescent drops lower and farther left when viewed at the same time each
morning. This morning, an hour before sunrise, Luna perches 15 degrees (11/2
fists) above due east. Two mornings from now, June 15th, the Moon is only 5
degrees above the east-northeast. That morning try to detect the Pleiades star
cluster just to the Moon's upper left.
The earliest sunrise of the year occurs today for latitude 40°N (approximately the
continental U.S.). Contrary to intuition, the earliest sunrise, latest sunset, and
longest day of the year do not coincide. The reason for this seeming
inconsistency is not straightforward to visualize. It stems from the fact that the
Earth's orbit is oval rather than circular and our planet's rotation axis is tilted
relative to its orbit instead of perpendicular.
Venus is emerging as a "morning star." Catch first sight of it tomorrow morning
25 minutes before sunrise. The thin crescent Moon sits about 5 degrees (half a
fist) above Venus, so it provides a helpful guide to the planet. Binoculars may be
necessary to pick out Venus. Binoculars will also reveal that Venus, like the Moon,
is now a crescent.
The constellation of Libra, the Scales, is familiar to many people as a member of
the zodiac. But its faint appearance makes the constellation much harder to know
as a pattern in the sky. The basic shape is a four-sided diamond consisting of 3
3rd-magnitude stars and one 4th magnitude. Libra poses due south near the end
of evening twilight. Look for it about 30 degrees above the horizon. The
constellation lies between the bright stars Spica, in Virgo, on the right, and
Antares, in Scorpius.
New Moon occurs at 4:27 p.m. EDT. Two weeks ago, when the Moon was Full, it
passed closest to Earth for 2004. At about noon today Luna reaches its farthest
point from Earth this year, 252,634 miles. The difference between these two
extremes, about 31,000 miles, is roughly 13 percent of the Moon's average
distance.
Look for the young crescent Moon about 45 minutes after sunset. At that time it
sits 3 degrees (6 moon diameters) above the horizon just to the right (north) of
west-northwest. Saturn rests 5 degrees to the lower left of Luna. Use binoculars
to help find both objects. This is likely the last sight of Saturn you will have for this
evening apparition.
Tonight the Moon visits the Gemini Twins. The bright star Pollux perches 2
degrees (4 moon diameters) to the crescent's upper right. Castor, the other twin,
is 4 degrees to the upper right of Pollux. Look for Mars, now at its faintest and
clearly dimmer than Pollux, 5 degrees to the Moon's left and slightly above.
Optimal time to look is 1 to 11/4 hours after sunset.
The solstice, known in the northern hemisphere as the first day of summer,
occurs at 8:57 p.m. EDT. Try this mental exercise. Where, approximately, on the
Tropic of Cancer would the sun be overhead at the moment of solstice, that is,
where is it about noon (1 p.m. Daylight Saving)? Since the solstice occurs about
9 p.m. in the Eastern Time zone, in California it would be around 6 p.m., and 3
p.m. in Hawaii. So the place we want is in the Pacific Ocean, a couple time zones
west of Hawaii. It turns out to be north of Wake Island.
The Summer Triangle, that pseudo-constellation composed of the bright stars
Vega, Deneb, and Altair, now dominates the eastern sky at nightfall. Most casual
sky gazers know that the Summer Triangle encompasses the real constellations
of Lyra, Cygnus, and Aquila. Two lesser-known minor constellations also fall
within the Triangle. Vulpecula, the Fox, contains no stars brighter than 5th
magnitude. Sagitta, the Arrow, has a few 4th-magnitude members. Look for them
some dark night with the help of a detailed star map.
The Moon sits 4 degrees (8 moon diameters) to the upper right of Regulus, the
bright star that marks the heart of Leo, the Lion. The beast's head is formed from
the partial circle of fainter stars to the Moon's upper right. The dominant object in
the area, Jupiter, is 13 degrees (a fist) to Luna's upper left. Tomorrow night look
for the Moon 2 degrees to the upper right of Jupiter.
The magnificent summertime constellation of Scorpius now appears low in the
south-southeast near the end of twilight. Antares, the brightest star in the group,
rises invisibly more than an hour before the sun sets, but the figure's tail doesn't
come up until 2 hours after sunset. Unfortunately, the scorpion never climbs very
high above the southern horizon for mid northern latitudes. The farther south you
are, the higher it ascends, passing overhead for observers in the middle region of
South America, for example.
Venus now rises about 11/4 hours before sunrise. If you look for the planet in the
next couple of weeks, be sure to notice the star Aldebaran, eye of Taurus, close
by. Tomorrow morning Venus sits 2 degrees to the upper left of the star, with both
objects low in the east-northeast. In early July the two bodies pull within a degree
of each other. By then they will also rise about 13/4 hours ahead of sunrise.
The Moon reaches First Quarter today. Study the Moon tonight after sunset and
determine if it appears slightly more or slightly less than half full. Then find the
time First Quarter occurs written at the end of this paragraph. The Moon sits
among the stars of Virgo, a rather long constellation. Luna was within Virgo last
night and will remain in the constellation for the next two nights. Tomorrow night
the Moon parks 4 degrees to the upper right of Virgo's brightest star, Spica. (FQ:
3:08 p.m.)
The constellation of Hercules crosses the meridian (due south) around midnight.
Then it stands just to the south of overhead, for mid northern latitudes. Hercules
lies between Arcturus and Vega but closer to the latter. Although not a bright
pattern, most observers learn to readily identify it from the distinctive "keystone" or
"wastebasket" shape. The wider end of the keystone is nearest the zenith. The
constellation is famous for M13, the bright globular star cluster it contains that's a
favorite target of amateurs.
If you missed the discussion earlier this month regarding the offset of earliest
sunrise and latest sunset from the solstice date (longest day), you may be
surprised to learn that the latest sunset occurs today for latitude 40 degrees
north. Most people find the event puzzling. Several places on the web provide a
thorough explanation, including www.analemma.com.
We usually speak of the North Star, or Polaris, as marking the exact position of
north. In actuality, it is slightly off true north, the point astronomers designate as
the North Celestial Pole. The fact that Polaris is even close to the pole is an
accident of time. Earth's rotation axis slowly wobbles, sweeping out a circle in the
sky in 26,000 years. Polaris is currently within three-quarters a degree of the axis,
a distance that will shrink to half a degree around the year 2100, As the wobble
continues, the distance increases, reaching almost 50 degrees 13,000 years
from now.
The waxing gibbous Moon passes Antares, the heart of Scorpius, during daylight
hours tomorrow. This evening it appears 5 degrees (half a fist) to the star's upper
right. Tomorrow night look for Luna 10 degrees to the lower left of Antares.
Antares is a colossal red supergiant star almost 500 times larger than our sun
and sitting at a distance of 600 light years away.
Mercury commences an evening appearance. If you'd like to be among the first to
catch a glimpse during this apparition, look just above the west-northwest horizon
45 minutes after sunset. The planet's now at magnitude 1.0 but still may require
binoculars to be able to pick it out of the twilight glow. Through July Mercury
maintains it altitude relative to sunset while slowly drifting southward. It also dims
by 11/2 magnitudes.
Please send any comments, suggestions, or questions to
Thomas G. Ferguson:
fergus52@msu.edu
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