To the reader:
The Skywatcher's Diary for May 2003 has been prepared by
David Batch. Credit to the author and to
Department of Physics and Astronomy at
Michigan State University, and mention of
Sky Calendar, would be
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can be viewed via the World-Wide Web at
If you would like a printed sample of the May issue, please send a long,
self-addressed stamped envelope to:
May Sky Calendar
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
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Skywatcher's Diary: May 2003
New Moon occurs at 8:15 a.m. EDT. It's the first of two New Moons this month. A
second Full Moon in a month is often dubbed the "blue moon." No such
recognition exists for the New Moon, or any other phase, for that matter.
Coincidentally, today also marks the most distant Moon of the year -- 252,605
miles or 31.9 earth diameters separate us. For comparison, the nearest Moon,
which happens in November, is 221,712 miles or 28.0 earth diameters away.
Incidentally, today's farthest Moon takes place around 4 a.m. EDT, just in case
you've got some ancient secret ceremony to observe.
Look for the 37-hour Moon low in the west-northwest, setting not quite 1 1/2 hours
after sunset. The delicate arc of light from such a young Moon is a captivating
sight. It's also easily missed because of the bright background twilight and the
Moon's low altitude. Best time to view is 30 minutes to an hour after sunset. You
might also enjoy the scene through binoculars.
The slender Moon stands 12 degrees (approximately a fist) above the west-
northwest horizon an hour after sunset. Six degrees to its lower left, look for the
star Aldebaran, eye of Taurus. The slightly brighter object 16 degrees to the
Moon's upper left is the ringed planet, Saturn. If you have access to a telescope,
you may want to take a good look at the planet before too many more days pass.
Soon it will be too low in the sky after sundown to provide a sharp, detailed
Tonight the Moon sits 5 degrees (10 moon diameters or half a fist) to the lower
right of Saturn. Tomorrow night look for the crescent 9 degrees above the planet
and slightly left. The Moon is approaching the phase where craters begin to
appear conspicuous in telescopic or binocular views. Can you detect the large
dark oval a third of the way from the Moon's northern (upper right) tip? Mare
Crisium (MARR-ay CRY-see-um) is an ancient lava lake that filled the floor of a
major crater. Mare Crisium occupies an area roughly the size of Michigan.
At 2 p.m. EDT the first day of fall begins for the northern hemisphere Š of Mars.
The Red Planet's southern hemisphere must, therefore, be coming out of winter.
Consequently, the south polar ice cap is near its maximum size. Coincidentally,
Mars' south pole is tipped toward Earth now, giving us a good opportunity to view
the cap in a telescope, even though the planet is still quite distant. Look for a
small bright spot on Mars' southern (lower right) limb.
If early morning skywatchers notice a few "shooting stars" this week, the meteors
are probably part of the Eta Aquarid shower. The event typically produces a
meteor every few minutes. The shower's maximum is broad, so there's not much
falloff over several days. To tell if the meteor belongs to the shower, trace the
streak of light backward to see if it appears to come from the area of the star Eta
in Aquarius, a quarter of the way up in the east-southeast in early dawn.
Mercury transits the sun today. The tiny silhouette of the planet slides across the
face of the sun for the first time since 1999. Unfortunately, the timing is bad for the
U.S. Only Alaska, just before sunset, and the extreme northeastern states, shortly
after sunrise, have any chance to catch a glimpse. A telescope that can safely
view the sun is required. For specific information regarding where and when the
transit can be viewed, go to
The Moon and Jupiter cavort this evening. Look for the pair in the west-southwest
more than halfway up, an hour after sunset. Jupiter appears 5 degrees (10 moon
diameters) above Luna. Both objects are within the boundaries of the
constellation Cancer, the Crab. If you center Jupiter in your binoculars' field of
view, the star below and slightly right of the planet is 4th-magnitude Delta in
Cancer. The scattering of stars farther to the right is the Praesepe or "Beehive"
star cluster. On a dark moonless night the group appears to the unaided eye as a
faint, fuzzy star.
The Moon reaches First Quarter this morning at 7:53 a.m. By this afternoon when
you can first catch sight of it, Luna should appear more than half full. Once
darkness sets in, you'll notice the stars of Leo surrounding the Moon. The
brightest star in the vicinity is Regulus, heart of the lion, and 6 degrees to the
lower left. The star to the Moon's left is 4th-magnitude Eta in Leo. Observers in the
western states will see the Moon occult (pass in front of) that star overnight.
Astronomy Day is celebrated today in communities around the world. Local
organizations sponsor public astronomy-related activities. It's an opportunity to do
some telescope viewing, join family activities, or find out about the regional
amateur astronomy club. Contact your local planetarium, science museum,
amateur club, or college to see what's happening. If you have difficulty finding
activities in your area, check with the Astronomical League, an affiliation of
amateur groups. Their website is http://www.astroleague.org.
Take a peek at Mars through a telescope sometime soon, if you are able. Don't
expect to see much surface detail, yet. That will come as we close in on Mars in
July and August. Instead, note the shape of the disk. It should appear to you
distinctly gibbous, that is, not completely circular. The planet is now 87 percent
full, a minimum that it reaches again in late December. Mars currently rises 4
hours before the sun. An hour before sunup it's the brightest object near
A bit of trivia: Jupiter and Saturn are 43 degrees apart. That figure is interesting
because it's the minimum separation of these two planets until 2018. From then
until December 2020, the planets continue to pull closer together. On December
21, 2020, the giant planets slide within 0.1 degree of each other. The duo should
be quite a sight, low in the southwestern sky after sunset. Be sure to mark your
calendar, if you can find one for 2020.
The star 5 degrees (10 moon diameters) to the lower right of the Moon this
evening is Spica, brightest of the constellation Virgo. The Moon is still two days
from Full, but it's already 94 percent illuminated, enough to seem Full to the
Diagrams for many of the events mentioned in this column, as well as May's
lunar eclipse, can be gotten by downloading a copy of the Sky Calendar from
The first total lunar eclipse visible from the continental U.S. in 3 years takes place
tomorrow evening. During a total eclipse, the Full Moon is dimmed when it
passes through the Earth's shadow. Part of the appeal of watching a lunar
eclipse is discovering the Moon's changing hues. Depending on the density of
the shadow, the fully eclipsed Moon may vary in appearance from an almost
invisible dusky gray to a bright coppery orange.
The lunar eclipse begins tonight at 10:03 p.m. EDT when the Moon enters the
darkest part of the Earth's shadow, called the umbra. A small nick initially
appears on the lower portion of the Moon. By 10:35 p.m. the Moon is half covered.
It is completely immersed in the shadow at 11:14 p.m. and reaches deepest
eclipse by 11:40 p.m. The process then reverses. The Moon begins leaving the
umbra at 12:06 a.m., is halfway at 12:46 a.m. and completely out by 1:17 a.m.
The Moon turned Full, technically speaking, last night at 11:36 p.m. EDT, during
the middle of the lunar eclipse -- a fact that will not surprise anyone who
understands the positions of sun, Earth, and Moon during an eclipse. Lunar
eclipses occur only at Full phase and solar eclipses only at New. An eclipse does
not occur at every New and Full Moon because the Moon's orbit is tilted 7 degrees
to Earth's, so most of the time the alignment of sun, Earth, Moon is not exact. The
precise alignment happens at approximately 6-month intervals. The next lunar
eclipse occurs on November 9.
The Moon is currently passing through the constellation of Scorpius. Last night
after moonrise, about 2 hours after sunset, Luna perched 3 degrees (6 moon
diameters) to the upper left of Antares, brightest star in the scorpion. Over night
the Moon slid another 2 degrees from Antares so that this morning before dawn 4
degrees separated Moon and star. Tomorrow morning Luna sits 11 degrees
above the tip of the scorpion's tail.
Now that the Moon is out of the evening sky, look for the Milky Way some evening
after twilight. Just kidding: You likely won't find it, or at least not easily. This time of
year after dark, the plane of the Milky Way sits level, so the Milky Way band circles
horizontally around us. The Earth and solar system lie in this flat disk of the Milky
Way. We travel around the center of the galaxy, similar to the way the planets circle
the sun. The direction we are headed, known to astronomers as the "solar apex,"
points roughly to the star Vega, currently low in the east-northeast.
Mars rises just after Jupiter sets, around 2 a.m. local time. With brilliant Jupiter
out of the picture, Mars becomes the brightest object in the sky, except, of course,
for the Moon. The Red Planet is well on its course to a spectacular late summer
appearance when it will outshine even Jupiter. Mars currently sits among the
stars of faint Capricornus, which only serves to intensify the planet's luster. Both
Neptune and Uranus are also in the vicinity, but too faint to locate without optical
aid and a good finder chart.
Tomorrow morning, an hour before sunup, look for Mars 7 degrees (less than a
fist width) to the upper left of the slightly gibbous Moon. The following morning
(Thursday) the two objects are nearly the same distance apart but the Moon has
swung to the other side of the planet. Look for it 7 degrees to the lower left of
Mars. The 3rd-magnitude star 3 degrees (6 moon diameters) above the Moon is
Delta in Capricornus, sometimes known as Deneb Algedi, the "tail of the goat."
Today the sun enters the astrological sign of Gemini, as those who follow
horoscopes would know. Astronomers, on the other hand, consider the sun to be
among the stars of Taurus, having crossed into that constellation on May 14. The
primary reason for this difference in reckoning is the wobble of the Earth's rotation
axis, often called "precession of the equinoxes." Like a spinning top slowing
down, the Earth's axis swings around in a circle, making a complete circuit in
26,000 years. As the Earth's axis sways, it carries with it the coordinate system
that we use to determine calendar dates relative to the stars. In essence, the daily
horoscopes ignore precession.
The Moon reaches Last Quarter phase at 8:31 p.m. EDT, so by the time it rises
tomorrow morning, about 3 a.m. local daylight time, it should appear slightly less
than "half full." Remember that the Last Quarter Moon marks the position in the
sky that the Earth is headed, in its orbit around the sun. The Last Quarter Moon
also leads the sun across the sky by approximately 1/4 day (6 hours).
The Big Dipper is currently near its maximum height, toward the end of evening
twilight. The popular figure is so high up, nearly overhead for mid northern
observers, that casual skywatchers may miss it. Remember that the Pointer
Stars, the two at the end of the bowl, can be used to find the North Star. Similarly,
the handle stars will trace an "arc to Arcturus," the bright star two-thirds of the way
up in the southeast, and "speed on to Spica," located slightly more than a third up
in the south. Spica is fainter than Arcturus, but still 1st magnitude.
Can you trace the plane of the solar system through the constellations? Roughly,
it's just a matter of following the zodiac. If you'd like a more precise tracer, several
of the bright objects now appearing in the evening sky will serve the purpose well.
Start with the planets. Saturn is low in the west-northwest. Slide to Jupiter, 43
degrees (about 4 fists) to Saturn's upper left. Move from Jupiter to the star
Regulus, in Leo, 18 degrees to the upper left. Next comes Spica, in Virgo, 54
degrees to the lower left, or 36 degrees up in the south. Lastly we arrive at
Antares, in Scorpius, just rising in the southeast.
Over the next several mornings, persistent observers can follow the dance of
Venus and Mercury in the east-northeastern sky. Venus is now quite low, and
Mercury's current appearance is poor for northern skywatchers. Nevertheless, the
event is worth your effort. The crescent moon slides through the area, too, adding
to the scene. Tomorrow morning, 40 minutes before sunrise, Venus sits 2 1/2
degrees (5 moon diameters) above the horizon between east and east-northeast.
Mercury is 2 degrees below Venus. Binoculars will be necessary for 1st-
Tomorrow morning, 40 minutes before sunup, the crescent Moon perches 9
degrees (a fist) above the eastern horizon. Look for bright Venus 18 degrees to
the Moon's lower left and 3 degrees above the horizon. Binoculars should reveal
Mercury 2 degrees to the lower right of Venus. Over the following two mornings
the Moon approaches and then passes the planets.
Forty minutes before sunrise tomorrow, look carefully for the thin crescent Moon 5
degrees (half a fist) above the eastern horizon, and 10 degrees left (north) of due
east. Venus is 20 degrees to Luna's lower left and Mercury 2 degrees to the lower
right of Venus. That puts Mercury a mere 1 degree above the horizon. Binoculars
are required to see Mercury. Continue watching as the planets climb higher and
the sky brightens.
Tomorrow morning the configuration of Moon, Venus, and Mercury is most
picturesque. The three objects form a compact triangle in which the top two sides
measure 2 1/2 degrees long. Forty minutes before sunrise Venus sits 3 degrees
above the east-northeast horizon. Mercury is to its lower right, and the Moon its
lower left. Timing is critical and binoculars are essential. Each day Mercury
appears farther above and to the right of Venus. In less than a month, Mercury
passes Venus again going the opposite direction, as it drops into the bright
twilight. That time the planets' separation will be less than a degree.
By the time evening twilight ends, all three stars of the Summer Triangle have
risen, a sure sign that summer is close at hand. Vega, the brightest of the group,
hangs about half way up in the east-northeast. Deneb, the faintest of the trio, sits
24 degrees (2 1/2 fists) to the lower left. Altair is the last of the Triangle to rise,
coming up more than an hour after sunset. Look for it low in the east.
Some clear night use binoculars to examine the area around Vega. Vega's the
brightest star in the constellation Lyra, the Harp, and sits a third of the way up in
the east-northeast an hour after sunset. About a degree and a half to Vega's left
and slightly lower (well within the binocular field), look for two 5th-magnitude stars
close together. You have located Epsilon Lyrae, the famous "double-double" star.
It has that nickname because under telescopic magnification each of the two
stars also transforms into a pair of stars.
New Moon occurs this morning at 20 minutes after midnight EDT. If you have
access to an observing site with a flat horizon, this evening you should try to
capture the under-24-hour-old Moon. Thirty minutes after sunset the hairline
crescent will appear 2 degrees above the horizon (higher on West Coast) and
approximately 15 degrees south (left) of northwest. The age of the Moon varies
from about 21 hours old on the East Coast to over 23 hours on the West Coast.
Observe with binoculars, and then try with unaided eye.
Please send any comments, suggestions, or questions to
Thomas G. Ferguson: