To the reader:
The Skywatcher's Diary for May 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 May issue, please send a long,
self-addressed stamped envelope to:
May 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: May 2002
For the last several weeks Mercury's orbit propelled it away from the sun.
Consequently, the planet became easier to find as it crept upward in the western
evening sky. Next week the planet will start becoming more difficult to spot, for two
reasons. It soon will reach the "bend" in its orbit and head back toward the sun,
and Mercury's brightness is diminishing rapidly. Seize the moment and look for it
now. An hour after sunset the planet sits 8 degrees above the WNW horizon and 5
degrees (half a fist) to the lower right of Venus, the brightest object in the west.
Mercury had been gaining on Venus each night, moving obviously closer to the
brilliant planet over the last week or two. Yesterday Mercury's apparent speed
dropped below Venus' so the separation between these two planets is now
growing. Venus will continue upward, eventually passing Saturn, Mars, and
Jupiter, while Mercury soon becomes obscured by twilight.
Two nights ago Saturn and Mars were at the same altitude. Faint Mars is now
noticeably higher than Saturn, 2 degrees to its left. Brilliant Venus is rapidly
gaining on the other two. Be sure to look every evening, about an hour after
sundown, to witness a rare grouping of these three planets. The trio is most
compact this Sunday and Monday evenings. Tonight Mercury rests 6 degrees (half
a fist) to the lower right of Venus. The 1st-magnitude star Aldebaran, eye of
Taurus, is 6 degrees to the lower left of Venus. Look for the Pleiades star cluster
4 degrees to the lower right of Mercury. Use binoculars.
The Moon attains Last Quarter at 3:16 a.m. EDT. Mercury also reaches the end of
its orbit today, so to speak. Astronomers call it "greatest elongation." The angular
separation between planet and sun is maximum (21 degrees) for this go round.
The swift planet will be in conjunction (in line) with the sun by May 27. If you could
get a good look at Mercury through a telescope, the planet would appear
approximately half illuminated, like the quarter moon, but similar to first quarter
(right half illuminated) rather than today's actual Last Quarter Moon with its left
side lit.
If you only once view the ongoing planet gathering, tonight is the night. Look in the
west-northwest an hour to an hour and fifteen minutes after sunset. Three of the
planets, Venus (brightest), Saturn, and Mars (faintest) form an almost equilateral
triangle less than 3 degrees (third of a fist) on a side. 2010 is the next time three
planets are similarly arranged. Mercury is 7 degrees to the lower right of the trio,
and Jupiter hovers 27 degrees to the upper left. All five planets reside within a
span of 36 degrees. A comparable grouping of these 5 planets doesn't occur
again until 2040.
The show continues. Watch the Venus-Saturn-Mars triangle change shape over
the next few evenings. Venus, the speedier of the threesome, has already
overtaken Saturn, and Mars is in its sight. Venus' pace is currently more than a
degree a day, so its apparent motion would be obvious even without the two
planets that serve as nearby markers.
Early risers can catch the thinning crescent Moon over the next several mornings.
An hour before sunup today the Moon hangs 6 1/2 degrees (13 moon diameters)
above the east-southeastern horizon. Tomorrow morning at the same time Luna
is only 3 degrees up and a few degrees to the south of due east. The next
morning (Thursday) the Moon waits just below the eastern horizon an hour before
sunrise. It rises a few minutes later. New Moon occurs Sunday morning.
Mercury is fading rapidly, more than a tenth of a magnitude per day. It is currently
1st magnitude (0.9, to be precise) and will drop to 2nd magnitude within the week.
You have little time left to observe the elusive planet. An hour after sundown look
for it 7 degrees above the west-northwest horizon and 7 degrees to the lower right
of Saturn. See if you can spot 1st-magnitude Aldebaran, eye of Taurus, 8 degrees
to the lower left of Mercury and 7 degrees below Saturn. Binoculars will help.
Tonight and tomorrow evening the big sky event: Venus passes within a third of a
degree (less than a moon width) of Mars. The glare from Venus, at magnitude
Ð3.9, will cause difficulty finding dim Mars (magnitude 1.7). Use binoculars or
observe earlier in brighter twilight to avoid the glare and more easily detect both
planets simultaneously. Tonight Venus is to the right and slightly below Mars.
Tomorrow evening Venus is almost directly above Mars. Can you determine by
observation which night the two objects are closest?
When two astronomical bodies appear close together, as Venus and Mars do this
evening, astronomers refer to the incident as an appulse. The event tonight is the
second closest planet pairing of the year. During the closest appulse, on the
morning of July 2, Mercury and Saturn appear only a tenth of a degree closer, so
the two near approaches are quite similar. The present event is easier to
observe, however, since Venus and Mars are higher than the Mercury-Saturn
grouping at the same stage of twilight.
Tonight an hour after sunset Venus sits three-quarters of a degree above, and
slightly to the left of Mars. The bright planet treks a bit more than a degree a day
relative to the background stars, and Mars travels half a degree per day against
the starfield. So Venus is now pulling away from the Red Planet at the rate of half
a degree a day. Next up for Venus is Jupiter, which it will reach in early June.
The Moon officially reaches New phase this morning at 6:45 a.m. EDT. The Moon
will still be too young to spot this evening, but with careful timing you may well find
it tomorrow. Look low on the west-northwestern horizon an hour after sundown.
The Moon then sits 4 degrees (8 moon diameters) above the horizon, 4 degrees
to the lower right of Saturn, and 3 degrees to the right, and slightly below, Mercury.
The Moon serves as a guide to help you get a final glimpse of Mercury before it
fades into twilight within the next few days.
The planet grouping now stands at its tightest configuration. All 5 planets fit in a
33-degree span. The collection is not as easy to see as last week, due to
Mercury. That planet has dropped more than a magnitude in brightness and 4
degrees in altitude since then. If you are motivated by record setting events,
however, you will want to make the attempt to see them all. The 5 naked-eye
planets will not be this close again until the year 2040. Look west-northwest, 45
minutes to an hour after sunset. The crescent Moon, by chance, aids the quest,
poised 3 degrees to Mercury's left. Binoculars may be needed.
The Moon and Venus pose for your camera tonight. The two brightest objects in
the nighttime sky sit less than 3 moon diameters apart. Begin watching the
twilight colors about 30 minutes after sunset in order to pick the most picturesque
moment. In an unusual happenstance, the Moon occults, or passes in front of, 3
planets today. The events occur in widely disparate locations, including the Arctic
Ocean and South Pacific. None of the occultations are visible from the U.S.
The 3-day-old crescent Moon sits between Venus and Jupiter tonight, two-thirds
of the way from Venus and one-third to Jupiter. Look for earthshine, sometimes
called "ashen glow." The faint gray light fills in the portion of the Moon that isn't
the crescent. Over the next 24 hours the Moon hopscotches over Jupiter, so that
tomorrow night it appears 7 degrees to the upper left of the planet. Notice then
that the Gemini Twins, Pollux and Castor, are 5 degrees above and to the left of
Luna.
Sometimes called invisible showers, radio meteors are detectable day or night,
rain or shine. A meteor streaking through the upper atmosphere leaves a trail of
ionized gas. You may receive radio signals from distant FM stations, more than
1000 miles away, as they bounce off these tracks. The Arietid meteors, a radio
shower, reach their peak today. For more information on this unusual hobby, see
http://www.imo.net/radio/.
With all the excitement over the planets, you may not have noticed Orion's
departure. Betelgeuse, the lone remaining bright star from that constellation, can
be spotted 5 degrees up in the west an hour after sunset. The rest of his winter
friends quickly follow suit. Last to leave will be the Gemini Twins and Capella,
from the constellation Auriga. A month from now they will sit low on the horizon at
dusk. By August, Orion begins his morning return, then rising just ahead of the
sun.
The Moon has crossed into the constellation of Leo, the Lion. It remains in that
figure for 3 nights. Regulus, the star marking the beast's heart, is 12 degrees (a
fist) to Luna's left. Tomorrow night the Moon sits 5 degrees above Regulus, and
slightly to its left. By Monday evening the Moon is 9 degrees to the lower right of
2nd-magnitude Denebola, the lion's tail.
The Moon attains First Quarter at 3:42 p.m. this afternoon. Tonight try to detect that
the terminator (line dividing lunar day from night) is not perfectly straight but
bowed ever so slightly to the left. Regulus is 5 degrees beneath the Moon. Find
2nd-magnitude Alphard 27 degrees (3 fists) below Luna. The name derives from
Arabic meaning "solitary one" because no other bright stars reside in this part of
the sky. Alphard belongs to Hydra, the Water Snake, a meandering string of faint
stars which are roughly parallel to the horizon in early evening.
This time of year the Big Dipper stands at its maximum height above the northern
horizon in early evening. To the casual observer the Dipper may appear to
straddle the zenith, or peak, of the sky, but for the continental U.S. it passes 10 or
more degrees to the north of overhead. Follow the curve of the Dipper's handle to
the brilliant yellow-orange star Arcturus, almost two-thirds of the way up in the
southeast. Continue the line to Spica, a third of the way up in the south-southeast.
For a star map to help locate these stars and their constellations, send a self-
addressed, stamped envelope to Sky Calendar, Abrams Planetarium, Michigan
State University, East Lansing, MI 48824.
An hour after sundown, look carefully at Arcturus and Spica, the brightest stars in
the southeast and south-southeast, respectively. Arcturus should be obviously the
brighter of the two and more yellow hued. Spica's color is often described as
blue-white, indicating a hotter star. It's surface temperature is around 40,000
degrees F. Arcturus, by comparison, is cool, only 7,000 degrees. Our sun, a
yellow star, is 10,000 degrees.
This evening the waxing gibbous Moon sits 10 degrees above and slightly right of
Spica. Arcturus is 28 degrees (3 fists) to the upper left of Luna. Tomorrow evening
the Moon slides 9 degrees to the left of Spica. Spica is the brightest star in Virgo,
one of the zodiac constellations. Since the Moon travels through the zodiac, it
passes near Spica each month. Occasionally the Moon occults (covers) Spica.
Arcturus, on the other hand, resides in Bootes, which is not a zodiacal pattern.
Consequently, that star can never be occulted.
And now there are three. Mercury first succumbed to twilight. Saturn is currently in
its last throes, setting an hour after the sun. An observer under the right sky
conditions might still glimpse it, but the excitement is gone. That leaves brilliant
Venus 15 degrees up in the west-northwest, bright Jupiter 11 degrees to the
upper left of Venus, and faint Mars 7 degrees to Venus' lower right. Since it is only
2nd magnitude, the Red Planet is already a challenge. Over the next month it and
Jupiter will drift toward the horizon, invisibly passing within a degree of each other
on July 2.
Locate Venus and Jupiter in the west-northwest an hour after sunset. Look
between the 2 bright planets for a 3rd-magnitude star. It is slightly above a line
drawn between the planets and a pinch closer to Venus. Although faint, the star is
the brightest one in that locality. It goes by the designation Epsilon in the
constellation of Gemini. In 4 days Venus will pass one-third of a degree from that
star. Follow the progress each clear night. Use binoculars.
Antares, heart of Scorpius, rises in the southeast shortly after sunset. Look for it
later, say 2 hours after sundown, when the sky is darker and Antares is higher,
making the star much easier to see. Tonight the Moon perches 11 degrees to the
upper right of Antares; tomorrow night it is 6 degrees to the star's left. Antares can
be thought of as the summertime counterpart to Betelgeuse. Both stars are red
supergiants, that is, they are enormous, cool stars Ñ the size of Earth's orbit or
larger and surface temperatures around 5000 degrees F.
A lunar eclipse occurs today, so what must be the phase of the Moon? Answer:
Full (7:51 a.m. EDT). Lunar eclipses occur at Full phase, solar eclipses at New.
The eclipse is minor Ñ what astronomers call a penumbral eclipse, which
means the Moon passes through the edge of the Earth's shadow. Penumbral
eclipses are generally unsatisfying. The Moon is only slightly darkened. The
casual observer probably would not notice. More bad news: this eclipse is visible
primarily from the Pacific, Australia and New Zealand. The western U.S. can catch
a glimpse of it at moonset.
Look carefully at Venus an hour after sunset. Can you spot the 3rd-magnitude star,
Epsilon Geminorum, 1 degree to the upper left of the planet? The glare from
Venus will probably necessitate using binoculars, but once you find the star with
optical aid, try it without. Tomorrow night Venus is even closer. Only one-third
degree separate the two, with Epsilon right of the planet. Continue to look the
following night (Wednesday) to spot the star 1 1/2 degrees to the lower right of
Venus.
Normally during this part of the lunar cycle, when the Moon doesn't rise for several
hours after sundown, we suggest planning a trip to a dark sky site to observe the
fainter celestial objects. The Milky Way Galaxy is often one of the items on the
observing list Ñ but not this month. The rim of the galaxy, which produces the
hazy band of light we recognize as the Milky Way, runs along the horizon in early
evening. Our atmosphere, densest and dustiest in that direction, obscures our
view. If you really must see the Milky Way, get up before dawn. But wait two weeks
for the Moon to leave the morning sky.
Venus and Jupiter are 5 degrees apart tonight, with Venus poised to overtake the
giant planet early next week. Watch every night to follow the progression. You
should still be able to recognize the Gemini Twins, 12 degrees (a fist) above
Venus. Try for Capella, 29 degrees to the right of Venus. Successful? Then look
for Procyon, the 0th-magnitude star in Canis Minor, the Little Dog. It sits 23
degrees to the left of Venus and 11 degrees above the western horizon an hour
after sunset.
All three stars of the Summer Triangle are observable 2 hours after sunset. Vega,
brightest and highest of the trio, is almost half way up in the east-northeast.
Deneb, tail of Cygnus, the Swan, hangs 22 degrees (2 fists) above the northeast
horizon. Altair, in Aquila, the Eagle, sits 8 degrees up in the east. This threesome
is the most identifiable celestial harbinger of warm summer nights.
Some night when twilight is almost over, look for four 3rd-magnitude stars that
highlight Corvus, the Crow. First locate Spica, the 1st-magnitude star a third to half
way up in the south 2 hours after sundown. Corvus is approximately a fist and a
half (15 degrees) to the star's lower right. The four stars form a trapezoid that's
approximately 6 degrees tall and narrower at the top than bottom. The shape is
sometimes called the "mainsail" because it is reminiscent of the sail on an
ancient sea vessel. A line connecting the top two stars, if extended to the upper
left, leads to Spica. That upper left corner star, Delta, is a double. The
components show contrasting colors, easy to pick out in a small telescope.
Please send any comments, suggestions, or questions to
Thomas G. Ferguson:
fergus52@msu.edu
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