To the reader:
The Skywatcher's Diary for March 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 March issue, please send a long,
self-addressed stamped envelope to:
March 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: March 2002
Since November of last year, Jupiter has retrograded among the stars of Gemini,
the Twins, moving 10 degrees westward in the last 4 months. Today the planet
resumes its usual eastward trek. Note the 3rd-magnitude star, Mu, in Gemini, 1
degree below Jupiter. The giant planet will now travel eastward through the zodiac
until December before retrograding once again. By then it will have traversed all of
Cancer and just crossed over into the constellation of Leo.
The bright star 5 1/2 degrees (half a fist width) below the Moon this morning is
Spica, the "ear of wheat" held by Virgo. Tomorrow morning the Moon moves into
the constellation of Libra, the Scales, one of the fainter zodiacal patterns. Third-
magnitude Zubenelgenubi, one of the two brightest stars in that constellation, is
then 6 degrees to the lower left of the Moon. This star is "double," a 3rd and 5th-
magnitude star that appear as one to the casual observer. Look carefully and you
may see the separate stars. Binoculars make them easy to "split."
With the Moon absent from the evening sky for the next week or so, you have a
good opportunity to view the zodiacal light. This faint glow rises out of the western
horizon at the end of twilight. Often it is mistaken for the Milky Way, but the
zodiacal light is pyramid-shaped, broadest near the horizon and narrowing with
altitude. It is caused by minute dust particles in the plane of our solar system.
These specks of rock catch sunlight and reflect a tiny amount of it in our direction.
The eye is just sensitive enough to spot some of the illumination in a very dark sky.
Tomorrow morning the almost-last-quarter Moon sits above Antares, the ruddy star
that marks the heart of Scorpius. Five-and-a-half degrees (11 moon diameters)
separate the two bodies. On Wednesday morning the just-past-last-quarter Moon is
14 degrees above the tip of the scorpion’s tail, denoted by a 2nd and 3rd-magnitude
star closely spaced. Thursday and Friday morning the Moon passes overtop the
stars of the "teapot" pattern in Sagittarius.
The Moon reaches Last Quarter at 8:24 p.m. EST. When the Moon is at this phase
it precedes the sun across the sky by roughly one-quarter day (or follows the sun
by three-quarters of a day, if you prefer). When, therefore, should we expect the
Moon to rise tonight? The answer is around the middle of the night (one-quarter
day before sunrise). Although time of year and latitude affect the details, each
phase has a general visibility pattern that is easy to learn, as our ancestors well
knew.
Venus hovers near the western horizon 30 minutes after sunset. Spot it 7 degrees
to the south of due west. At that time 4 bright planets span 98 degrees across the
sky. Jupiter will be easiest to find, two-thirds of the way up in the southeast. Venus
is technically brighter, but its low altitude and brighter background sky diminishes
the planet's brilliance. Saturn sits 27 degrees (almost 3 fist widths) to the west of
Jupiter. Mars, faintest of the group at magnitude 1.3, is almost between Saturn and
Venus. Watch the quartet draw closer together through this month and next.
You have a few more moonless evenings to enjoy the "deep sky" wonders of
winter, those fainter, more subtle objects that amateur astronomers crave. The
Great Nebula in Orion is a perfect example. From a dark location, look 5 degrees
(half a fist) directly below Orion's 3 belt stars. Another series of fainter stars, often
called "Orion's sword" runs vertically in this area. In the middle of the sword region,
look for a soft glow. To the unaided eye it appears as a star you can't quite get in
focus. The nebula is better in binoculars and telescopes, but don't expect to see
the brilliant colors portrayed in photographs of this famous object.
The area of the sky often referred to as the "face of Taurus" contains a star cluster
named the "Hyades." It is the V-shaped pattern about 20 degrees (two fists) to the
upper right of Orion. The brightest object in that area is Saturn -- a visitor to Taurus
and not part of the cluster. The second brightest object is Aldebaran. That star is
also not a cluster member. Most of the rest of the stars you can see in that vicinity
are associated with the group, which has more than 100 members. This nearby
collection is so close we tend not to recognize it as a cluster, unlike its famous (and
more distant) neighbor 10 degrees to the left -- the Pleiades star cluster.
Tomorrow morning is the last opportunity to easily see the thin crescent Moon
before it becomes New. Look for it 30 minutes before sunrise near southeast. At
that time the Moon will be 6 degrees (12 moon diameters) above the horizon and
no challenge to spot unless landscape features conceal it. You could find the Moon
earlier but by choosing this time, you also have the chance to nab Mercury, 17
degrees to the Moon's lower left and only 1 degree off the horizon. Use binoculars
to help locate the planet.
Have you ever noticed a sun halo? The ring around the Moon is more obvious but it
occurs no more frequently than the sun ring. In both cases the rings are caused by
hexagonal ice crystals high in the atmosphere that reflect and refract the sunlight
(or moonlight). Even on clear days enough ice crystals may be present to create
the effect. Part of the trick to seeing the halo is remembering to look. The ring has a
22-degree radius (about two fists). Cover the sun so your eyes are shielded from
direct glare, and then use your fist to measure out to the proper distance and
search carefully. For more extensive information visit
http://www.sundog.clara.co.uk/atoptics/phenom.htm.
The Big Dipper begins its climb up the sky as darkness falls this time of year. It is
easy to spot in the northeast, standing on its handle. Thirty degrees (three fists) to
its left is that famous 2nd-magnitude star, Polaris, the North Star. Another 30
degrees beyond is Cassiopeia, a group of 5 stars that suggests a letter "W" or "M."
It, like the Big Dipper, is standing on end with the "W" opening toward Polaris. A
line drawn through the middle of both constellations and Polaris is approximately
parallel to the horizon in early evening.
Jupiter reaches its greatest northern declination today, an event that will not
happen again for almost 12 years. The occasion, admittedly, is not something to
pop a cork over unless you are a Jupiter aficionado. For the average sky watcher it
does mean, however, that Jupiter will appear high in the sky, about 70 degrees up
for mid northern latitudes. Jupiter's path across the sky tonight, in fact, is the same
route followed by the sun on the summer solstice, when its path is highest for the
year.
The Moon reaches New phase this evening at 9:02 p.m. EST. Shortly after that
time, another moon event occurs, but involving two of Jupiter's satellites rather than
Earth's. Starting at 9:15 p.m. the moon Ganymede casts its shadow on the disk of
Jupiter, a phenomenon visible in modest size telescopes. At 12:13 a.m. a second
shadow, that of the moon Io, starts its journey across the planet's disk. For a few
minutes -- until Ganymede's shadow leaves the disk at 12:25 a.m. -- we witness
what astronomers call a double shadow transit. Finally, Io's shadow disappears at
2:28 a.m.
The Muslim New Year may begin tonight at sunset. The uncertainty arises because
the Islamic calendar is lunar based, and events begin at the first sighting of the
crescent Moon after New phase. While a North America sighting might be
possible, the Moon will not be visible on this date from the Middle East. Unlike our
civil calendar, which always begins in the winter, the Muslim calendar regresses
about 11 days earlier each year in order to keep pace with the sequence of moon
phases.
The crescent Moon is easy to locate tonight. Look low in the west. An hour after
sunset the Moon sits about 5 degrees (half a fist) off the horizon. Venus can be
found 7 degrees to the lower right of Luna, almost on the horizon. If your vista
toward the west is cluttered, you can begin observing sooner, as early as 30
minutes after sundown. Twilight will be brighter, so carry along binoculars to help in
the initial sighting.
Tonight the Moon is pleasantly located between Venus, 17 degrees (a fist and a
half) to the lower right, and Mars, 14 degrees above. If you want to glimpse both
planets, look before the end of twilight since Venus sets a little more than an hour
after sunset. If you noticed the Moon last night, see if you can predict where to find
the Moon tomorrow evening.
The 1st-magnitude "star," 4 1/2 degrees (9 moon diameters) to the upper right of the
Moon is the planet Mars. Can you detect a slight ruddiness in the planet's color?
Compare it to the Moon, to Betelgeuse (the right shoulder of Orion), to Rigel (his
left foot). What differences to you notice? The colors are subtle, but with a little
experience, the various tints will be obvious.
For a star map to help you locate these objects, send a self-addressed, stamped
envelope to Sky Calendar, Abrams Planetarium, Michigan State University, East
Lansing, MI 48824.
Tonight the Moon sits 10 degrees (a fist) to the upper left of Mars and 18 degrees
to the lower right of Saturn. Use binoculars or a telescope to more carefully
examine the Moon. The dark patch on the terminator (left edge) about halfway
between top and bottom is Mare Tranquillitatis, the Sea of Tranquility, made
famous by Apollo 11. The landing site is to the left side of Mare Tranquillitatis and
remains in darkness until after moonset tonight.
The Moon approaches Saturn tonight, 5 degrees (10 moon diameters) to the
planet's lower right. Early tomorrow morning, long after it has set for us, Luna
passes Saturn. The Moon occults (covers) the planet for some places on Earth.
The closest such location is western Alaska. Also tonight, the asteroid Vesta
appears so close to Saturn it could be easily mistaken for one of the planet's
moons. If you want to see this 8th-magnitude minor planet, you will need a
telescope. Look about 8 ring diameters due east of Saturn.
Spring officially begins with the Equinox this afternoon at 2:16 p.m. EST. The sun
passes from the southern hemisphere to the northern, bringing additional sunlight
and heat to the chilled northern climes. At the exact moment of the equinox the sun
stands overhead for a location on the Earth’s equator in the Pacific Ocean a few
hundred miles west of the coast of Ecuador.
This evening the first Moon of spring, a waxing crescent, poses 8 degrees (a fist) to
the upper left of Saturn and 19 degrees to the lower right of Jupiter.
The Moon is exactly First Quarter at 9:28 p.m. EST, so you are able to observe it at
the precise moment, if you wish. There's no astronomical reason to do so, but you
shouldn't look at the Moon only for astronomical reasons. The Moon is 6 degrees
(12 moon diameters) to the lower right of Jupiter early tonight and 8 degrees to the
upper left of the giant planet tomorrow night. During the interim the Moon passes in
front of the planet as seen from Greenland, the Arctic Ocean, and northwest
Canada.
The official calendar for the country of India (Saka calendar) celebrates its new
year (1924) today. The calendar counts its years from the vernal equinox of 79 CE,
which occurred on March 22 that year. The Moon is among the stars of Gemini,
tonight. The two brightest stars of that constellation are 11 degrees (a fist width) to
the Moon's upper left. Eight degrees to the right (and slightly lower) sits Jupiter. The
giant planet is among the stars that mark the twins' feet.
Tonight the Moon is in line with the bright Gemini Twin stars. Pollux is 6 degrees
(12 moon diameters) to Luna's upper right, and Castor is another 5 degrees to the
upper right of Pollux. Procyon, the brightest star in Canis Minor, the Small Dog, is
19 degrees (two fists) to the Moon's lower right. Use binoculars on the Moon to try
to detect the crater Copernicus, a bright spot near the terminator (left edge) and
just above center. Hold the binoculars steady, or mount them on a tripod for a
better view. A telescope reveals the splendor of this magnificent crater.
If the air is particularly steady tonight (what astronomers call "good seeing"),
examine Jupiter with a telescope. The Great Red Spot, a large oval storm system,
will be crossing the middle of the planet’s disk, a little below center, at 10:44 p.m.
The feature was named more than a hundred years ago, when it appeared quite
red, by all accounts. In recent decades the color has faded to a lighter brown,
making the Spot more difficult to, er, spot. The Great Red Spot rotates around
Jupiter in about 10 hours. For other times when the Spot crosses the planet see:
http://skyandtelescope.com/observing/objects/planets/article_107_1.asp.
An hour after sunset the waxing gibbous Moon stands more than halfway up in the
east-southeast. Five degrees (10 moon diameters) below and slightly to the left of
the Moon look for Regulus, the brightest star in Leo. One degree to Luna's left, try
to spot the 4th-magnitude star Eta. Binoculars will help. Within 2 hours the Moon will
pass less than a moon diameter underneath the star. Near closest approach you
should be able to detect the Moon’s motion within a few minutes.
Sundogs, or parhelia, are bright spots about 20 degrees on either side of the sun.
They show up when high altitude ice crystals catch the sun's light. During better
displays the sundogs show color -- red toward the sun and blue away. The
phenomenon is related to the halo sometimes seen around the sun and Moon.
Even if the sky seems perfectly clear, there may be enough ice crystals to produce
the effect, so look carefully each day that isn't completely overcast, especially
within a couple hours of sunrise and sunset when the sun is low in the sky.
Mars officially drops to 2nd magnitude today. It continues to fade slightly through the
middle of 2002, as we pull farther away from the Red Planet. By January of 2003
Mars regains 1st magnitude status and keeps on climbing in brightness until its
opposition (close approach) to Earth in August 2003. An hour after sunset look for
Mars about a third of the way up in the west. Venus is 27 degrees (almost 3 fists) to
the lower right, almost on the horizon, and Saturn is 22 degrees to the upper left.
The Full Moon occurs at 1:25 p.m. EST this afternoon. Ten hours earlier the Moon
passed perigee (closest to Earth) during this month’s orbit. It is the second closest
perigee for the year -- 221,836 miles. Because this perigee happens so close to
the time of Full Moon, larger than usual tides are expected on the seacoasts. The
Moon rises just a few minutes after sunset within a degree of due east. A couple
hours after moonrise look for Spica, the brightest star in Virgo, 12 degrees below
the Moon.
One-and-a-half hours after sunset watch for moonrise, about 10 degrees to the
south (right) of due east. The star Spica rises 10 minutes before the Moon, another
5 degrees farther south. Arcturus, the brightest star in Bootes, the Herdsman, and
more luminous than Spica, is 27 degrees to the Moon's upper left. Arcturus and
Spica are two of the three most prominent springtime stars. The other is Regulus in
Leo.
Notice the star field in the vicinity of Jupiter tonight. The giant planet lies on a line
between two 3rd-magnitude stars. Mu, in Gemini, is 2 degrees below and slightly
right, while Epsilon is 3 1/2 degrees above and a tad to the left. Jupiter's orbital
motion will gradually carry it out of alignment with these two stars. Watch every
night and determine how soon you perceive a clear misalignment. You may prefer
to use binoculars.
Easter Sunday for the Christian world, today is also the last Sunday in March. If you
live in Great Britain, remember to set your timepieces ahead one hour, shifting from
Standard Time to Summer Time. Most of us in the U.S. must wait until next
Sunday, the first one in April, to force our clocks to "spring forward." The Moon
rises 4 hours after sunset, tonight. Look for it tomorrow morning before sunrise less
than a third of the way up in the south. The Moon sets 2 1/2 hours after sunrise in
the west-southwest.
Please send any comments, suggestions, or questions to
Thomas G. Ferguson:
fergus52@msu.edu
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