To the reader:
The Skywatcher's Diary for January 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 January issue, please send a long,
self-addressed stamped envelope to:
January 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: January 2004
Venus has quietly taken over the early evening sky. For so long, the planet hugged
the western horizon at dusk, making it difficult for the casual observer to spot.
Now setting more than 2 1/2 hours after sunset, Venus is difficult to miss. Blazing
in the southwest at magnitude -4.0, it outshines Jupiter, its next most luminous
planetary rival, by nearly 2 magnitudes. The planet remains easily visible until late
May.
Jupiter is best seen in the morning sky, ahead of dawn. An hour before sunrise it
sits halfway up in the southwest. The giant planet is gradually moving into the
evening. It currently rises 5 1/2 hours after sunset, and that time span will halve by
the end of the month. Jupiter officially resides in the constellation of Leo, south of
the triangle of stars that marks the lion's hindquarters. Look for 4th-magnitude
Sigma in Leo, half a degree north of the planet. Binoculars may help. In two days
Jupiter begins retrograding, that is, traveling westward against the background
stars. It will be early May before the planet resumes direct, or eastward, motion.
The Moon sits between Aldebaran and the Pleiades star cluster tonight, all part of
Taurus, the Bull. Aldebaran is the bright yellow-orange star 9 degrees (a fist
width) below the Moon. The star cluster lies 5 degrees above. Because Luna is
so bright, binoculars may be necessary to spot the Pleiades. Spirit, the first of two
U.S. Mars Rover spacecraft, will touch down on the red planet this evening if all
goes according to plan. For Quadrantid meteor shower info, see tomorrow.
The Quadrantid meteor shower peaks this morning just after midnight but is
severely hampered by moonlight. The Earth also reaches perihelion today, our
closest approach to the sun for this year -- 91.4 million miles. Contrary to
common belief, the seasonal temperature changes are not related to the varying
distance between Earth and sun. The difference between perihelion and aphelion
(greatest Earth-sun distance) is not significant enough to noticeably affect
temperature on Earth.
Although the shortest day of the year occurred two weeks ago, this morning
marks the latest sunrise for latitude 40 degrees north. The lengthening day soon
becomes noticeable as the rate of change picks up. Currently each day brings a
minute of additional daylight. By the end of January we acquire more than two
minutes per day. Clearly, winter is not over, but the lengthening day gives hope,
as it once did to our earliest ancestors.
Early birds may have noticed the nearly Full Moon rising in this morning's twilight,
with Saturn 8 degrees (16 moon diameters) to its upper left. Tonight look for the
pair about 20 degrees up in the east-northeast as dusk settles in, but separated
by only 4 degrees. This time Saturn is to the lower right of Luna. The bright
Gemini Twins are 13 degrees to the left, and the head of Orion about 20 degrees
to the right.
The Moon officially reaches Full at 10:40 a.m. EST. It won't be visible until tonight
when it rises around sunset. Once the Moon climbs above the treetops, an hour
or so after sunset, look for Pollux and Castor, the Gemini Twin stars, to Luna's
left. Pollux is 3 degrees (6 moon diameters) due left, and Castor sits 6 degrees to
the upper left. The Full Moon of January was known in colonial times as the "Old
Moon" or "Moon after Yule,"
Tonight the Moon rises about an hour later than last night. Watch for it to come up
a little right of northeast. Tonight the Moon lies within one of the faintest
constellations, Cancer, the Crab. Cancer contains no stars brighter than 4th
magnitude. To amateur observers, the constellation is probably best known as
the home of the Praesepe, or "Beehive," star cluster. Tonight, however, bright
moonlight will make the Praesepe difficult to locate.
The first asteroid to be discovered was Ceres. The Italian astronomer, Giuseppe
Piazzi, found it on January 1st, 203 years ago. Ceres reaches opposition today.
That's astronomer's jargon, which indicates that Ceres is in the middle of its
period of best visibility. The minor planet is now at its brightest, magnitude 6.8 --
still below naked-eye visibility. It is conveniently located 2 degrees from Castor, in
Gemini, but to find it you'll still need a good finder chart and binoculars.
The Moon rises 3 hours after sunset, among the stars of Leo, the Lion. Once
Luna gains altitude, you'll be able to spot Regulus, the brightest star in Leo, 4
degrees (8 moon diameters) to the Moon's right. A little later, Jupiter rises 18
degrees (2 fists) below the Moon. Thereafter you'll be able to follow those three
objects the rest of the night. Look for them in the west at dawn. By then, the Moon
and Regulus are 7 degrees apart.
The Moon cozies up to Jupiter tonight. The pair rises about five hours after sunset.
Luna pops into view first, with the giant planet appearing half an hour later, 5
degrees to its lower right. By daybreak tomorrow, the Moon has scooted to within
3 degrees of Jupiter. An hour before sunrise the duo perches halfway up in the
southwest.
Mercury is currently making a respectable showing in the morning sky. This week
the view is optimal. An hour before sunrise, look for the swift-moving planet 5
degrees (half a fist) above the southeastern horizon. It will be the brightest object
in the area. With steady air, a telescope can reveal that Mercury appears half full.
That shape indicates the planet must be nearing its greatest western elongation,
which occurs this Saturday, the 17th.
The Moon is close to Last Quarter tomorrow morning. (It officially reaches that
phase tomorrow evening at 11:46 p.m. EST.) Before sunrise tomorrow, the bright
star Spica, in Virgo, sits 9 degrees (a fist) to the lower left of the Moon. Luna
passes within 4 degrees of the star tomorrow evening, while it's below the
horizon for the U.S. Once it rises, after midnight local time, star and Moon are
separated by 4 degrees. By dawn the following morning, the span is 7 degrees.
Today is New Year's Day, if you keep track of time as Julius Caesar did. The so-
called "Julian Calendar" worked well over the short term, but accumulated an
error of one day every 128 years. Eventually the disparity between the Julian
Calendar and the seasons became intolerable. In 1582 the Gregorian Reform
was proposed, eventually widely adopted, and is what most countries, including
the U.S., use today for conducting civil affairs.
Venus passes within 1 degree of Uranus. It's an opportunity to locate the 6th-
magnitude planet with binoculars, using Venus as a marker. Uranus appears to
the right and slightly below Venus. There's a star one magnitude fainter than
Uranus to its upper left, about one-quarter of the Venus-Uranus distance away.
Another star, half a magnitude brighter than the planet, sits half the Venus-Uranus
distance to the right. The scene changes significantly by tomorrow night.
The waning crescent Moon passes through Scorpius during the next two days.
Tomorrow morning Luna sits near the leading edge of the scorpion, although
technically in Libra, the Scales. Look to the lower left of the Moon for the telltale
string of stars that trace the scorpion's body. Antares, the brightest star in that
string, is 12 degrees (a fist) away. The following morning the Moon passes 3
degrees (6 moon diameters) to the left of that star.
Mars just dropped to 1st magnitude. It hasn't been this faint since last April. On the
other hand, 1st magnitude is respectable. Mars is the brightest object in the
southern sky in the early evening. Nothing of comparable luminosity is within 45
degrees (4 or 5 fists) of the Red Planet in any direction. So enjoy the memory of
Mars' spectacular appearance last summer, but don't neglect the current view.
Tomorrow morning is the last practical opportunity for most northerners to catch
the thin crescent Moon before it turns New. An hour before sunup, the dainty sliver
of Moon perches 5 degrees (half a fist) above the southeastern horizon. It's also
an excellent chance to see Mercury. The planet sits 10 degrees to Luna's left. The
following morning some observers, particularly those in southern states, can
glimpse a hairline crescent, 8 degrees below Mercury. Look with binoculars 25
minutes before sunrise.
Most sky observers are familiar with the constellation of the Flying Horse,
Pegasus. There's another, smaller horse pictured in the same part of the sky, to
the right (west) of Pegasus. It's known as Equuleus (ee-KWOO-lee-us), the Little
Horse, or Foal. A first encounter with this constellation's name usually causes
people to hesitate, while their mouth attempts to form the word. Once learned,
though, the pronunciation flows easily off the tongue. Try it.
Equuleus is a small and faint constellation, so if you've never seen it before, you'll
want to drag out a star map for orientation. Its brightest star is only 4th magnitude.
The principle stars form a trapezoid between the nose of Pegasus and
Delphinus, the Dolphin. At the end of evening twilight, the constellation sits 10 to
15 degrees above the western horizon.
The Moon passes New phase at 4:05 p.m. EST. Yesterday the sun entered the
constellation of Capricornus, the Sea Goat. Later the same day in entered the
sign of Aquarius. Constellations are irregularly shaped patches of sky useful to
astronomers to broadly describe the location of a celestial object. In contrast, the
signs that astrologers and horoscopes use are all equal size.
The "first moon after new" is visible tonight shortly after sunset. Look for it low in
the southwest. Thirty minutes after sunset, it's 3 degrees above the horizon and
12 degrees to the north (right) of due southwest. Tomorrow night the young
crescent Moon is easier to spot. An hour after sunset it's 10 degrees (a fist) above
the horizon. As the sky darkens, note the Moon's distinctly 3D appearance that's
created by the ashen "earthshine" contained within the crescent.
Saturn reached a 15-year brightness peak in late 2002. Currently it is only two-
tenths of a magnitude off that record. In other words, Saturn is essentially as
bright as it ever gets. Coupled with the planet's late afternoon rising time that puts
it 40 degrees (4 fists) up in the east by nightfall, now is prime ring time, as in
Saturn's rings. Find a telescope and take a look.
Venus and the Moon make a pretty sight tonight. Four degrees (half a fist)
separate the picturesque pair in the southwestern dusk. They set about 3 hours
after sundown, so you have ample time to enjoy the scene. For a daytime view,
use the Moon to locate Venus before sunset. The second U.S. Mars Rover,
named Opportunity, will set down on the Martian soil this evening, if all goes well.
The famous variable star Algol, or Beta in the constellation of Perseus, is near
overhead at the end of evening twilight. Algol is actually a pair of stars orbiting
each other. As they perform their cosmic dance, the stars periodically pass in
front of and behind one another, causing the combined luminosity to vary from
magnitude 2.1 to 3.3 over a period of 2.9 days. Tonight at 9:12 p.m. EST, Algol
reaches its faintest.
Winter is prime time for halos and sundogs. A thin layer of high altitude cirrus
clouds creates these atmospheric phenomena. The clouds, composed of ice
crystals, bend and scatter light from the sun and Moon, resulting in a variety of
optical effects. Rings around the sun or Moon (halos), and colorful, rainbow-like
patches on either side of the sun (sundogs) are two of the most common
manifestations. Stay alert and you are bound to see them.
Look for Mars tonight, 4 degrees (8 moon diameters) above the Moon in early
evening. The Moon skitters past the planet overnight. By tomorrow evening Luna
lies 10 degrees (a fist) to the upper left of Mars. During that time the Moon
crosses from the constellation of Pisces, the Fishes, into Aries, the Ram, as it
approaches First Quarter.
The Moon reaches First Quarter overnight, technically tomorrow morning at 1:03
a.m. EST. -- just about the time it sets in the Eastern time zone. From an orbital
viewpoint, when it is at First Quarter, the Moon trails the Earth. That is to say, Luna
sits opposite the direction that the Earth is traveling on its journey around the sun.
When we gaze at the First Quarter Moon, it's as though we're looking out the "rear
window" of spaceship Earth.
Tonight Jupiter rises at nearly the same time Venus sets. Currently, Venus sets
about 2 minutes later per night and Jupiter rises 4 minutes earlier, so the length
of time the two planets are simultaneously above the horizon increases by 6
minutes daily. Within the next few nights it should be possible to view both
planets at the same time. When will you first see them?
An hour after sunset the slightly gibbous Moon sits 3 degrees (6 moon
diameters) beneath the Pleiades star cluster. Use binoculars to view the cluster
in the moonlight's glare. The Pleiades contains a few dozen stars, all relatively
young, around 100 million years old. The cluster lies about 400 light years from
Earth. Tomorrow night the Moon appears 11 degrees (a fist) to the lower left of the
Pleiades and 8 degrees to the upper left of the bright star Aldebaran, in Taurus.
Jupiter is a fine sight in a telescope. The giant planet appears larger and brighter
than average. Jupiter is moving more than 800,000 miles closer to us each day,
on its way to its closest approach in early March. Its four brightest moons make
fascinating viewing as they scurry around the planet. They noticeably move in a
few hours or less. These bright moons can even be detected in binoculars that
are held rock steady.
Please send any comments, suggestions, or questions to
Thomas G. Ferguson:
fergus52@msu.edu
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