From the March 2006 issue

Solar disappearing act

March 2006: Bodies in the solar system are constantly on the move. A pair of eclipses just skims the surface of the many dynamic events visible this month.
By and | Published: March 1, 2006
Baily's Beads
Baily’s Beads highlight the final seconds before the Moon blocks the Sun’s photosphere during a total solar eclipse.
Fred Espenak
One of nature’s grandest spectacles, a total eclipse of the Sun, greets observers in the Mediterranean region March 29. With all the fascinating things to watch — the corona, Baily’s beads, shadow bands, and projected solar crescents — it’s easy to miss the physiological effects on the body. The rapidly plunging light levels just before totality often trigger a weird mixture of excitement, panic, and foreboding. As soon as sunlight returns, unbridled elation and quiet personal reflection are normal. It’s different for each person, and from one eclipse to another.
Compared with last April’s oceanic totality, this eclipse crosses reasonably accessible land with mostly favorable weather conditions. If you can’t make it to this eclipse, start planning for the long-lasting, nearly 7-minute total eclipse that will cross the Far East in July 2009. There are no total solar eclipses in 2007, and the only one in 2008 crosses the Arctic before heading south through Siberia into China.

A different event arrives the evening of March 14 this year, when the Moon passes into Earth’s penumbral shadow. Observers from the Rockies eastward can catch the eclipse’s end as the Moon rises shortly after sunset. Folks farther east get a longer view. At no time will a dark bite be taken from the lunar disk, but on close inspection, you should see a grayish shading. The normally bright highlands across the Moon’s southern hemisphere will be dimmed, giving the whole disk a flat appearance.

Most noticeably, the Moon will take on a yellowish tinge close to mideclipse, at 6:48 P.M. EST. When the rising Moon shines through the lower layers of our atmosphere, it’s often painted a pale yellow to pink as a matter of course, but the penumbral shading should make this effect stronger.

Be sure to catch Mercury early this month, before it disappears from view. The solar system’s fastest planet is easy to pick out of the twilight after sunset, low in the west. Don’t wait, because it fades quickly in the last week of February, making a switch to binoculars necessary in early March. No bright stars lie nearby to confuse the planet’s identity.

Saturn perches high in the southeast as twilight fades, and the view improves through late evening because you have less of Earth’s atmosphere to peer through. The golden beacon lies off the western edge of the Beehive star cluster (M44), a nice binocular jewel. The ringed wonder is an awesome sight in any telescope. Zoom in on the gas giant to see the globe casting a shadow on the rings. This gives the planet a noticeable 3-D appearance.

Mars, although it’s bright and lies high in the sky, will be a disappointment to telescopic observers. Earth has pulled far ahead of the planet, and all that remains is a tiny, rust-colored dot with barely discernible low-contrast markings. Instead, enjoy the Red Planet’s appearance to the unaided eye, as the planet tracks slowly east of the Pleiades star cluster (M45) and north of the similarly colored bright star Aldebaran.

Mark your calendar for April 1. Early that evening, a gorgeous crescent Moon filled with earthshine will pass through the Pleiades. Whether you use binoculars or a telescope, you’re sure to get a great view. More details will appear in next month’s Astronomy.

The spring, or vernal, equinox happens March 20 at 1:26 P.M. EST. This marks the moment when the Sun’s center crosses the celestial equator. If the Sun were a point of light, we would have 12 hours of day and 12 hours of night. Because the top peeks above the horizon before the center rises, the day is actually a bit longer than the night. The media seem to enjoy creating hoopla surrounding the equinox. For stargazers in northern climes, however, it’s all about spending milder nights under the stars.

The deep sky

Run the marathon
March is the month when many stargazers attempt an annual Messier marathon. Why now? Most Messier objects just happen to be located away from the Sun’s glare at this point in Earth’s orbit, but you can’t deny the fact that spring nights are much more enjoyable than winter’s debilitating cold.

It all started in the 1700s, when French comet-hunter Charles Messier kept stumbling across star clusters and nebulous patches while searching for and following comets. His catalog of non-comets has stood the test of time as the “top 109” deep-sky objects. Many splendors still go by their Messier number. After all, M42 is easier to say than “The Great Orion Nebula.”

In the 1970s, observers realized it’s possible to see all the Messier objects in one night, from dusk to dawn, and Messier marathoning was born. “Take a deep-sky treasure hunt” on page 74 will help you plan an observing strategy. And plan you must; otherwise, some objects will set while you search for others.

Also known as NGC 628, M74 is about 35 million light-years away in the constellation Pisces the Fishes. It is estimated to be the home of about 100 billion stars, making it slightly smaller than our Milky Way Galaxy. This view is a composite of images taken on the night of August 13-14, 2001, with the 8-meter Gemini North telescope and the Gemini Multi-Object Spectrometer.
Gemini Observatory / GMOS Team
Because moonlight and city skyglow will hide the fainter Messier objects, you need to head to the country during the last week of March, when the Moon is almost new, to have a successful Messier marathon.

Author and observer David Levy discourages “sprinting.” There’s time to take a couple of minutes to jot down some notes on the structure and features of each Messier object. If you start with some of the bright, splashy star clusters early in twilight, you won’t have to rush later on. There’s even time for a refreshing nap after midnight, before the homestretch of summer clusters and nebulae toward dawn.

The spiral galaxy M74 is one of the most challenging objects during the marathon. You’d think with stats like a magnitude of 9.4 and a diameter of 11′ (one-third the Moon’s apparent diameter), it would be easy to see. However, when you look for it during twilight, as you must this time of year, the outer arms and circular glow disappear, leaving only the galaxy’s inner region as a faintish “star” with a small halo.

Comet C/2005 E2 (McNaught)
Comet C/2005 E2 (McNaught) passes near the galaxy M74 this month. The two look similar through a small scope.
Astronomy: Roen Kelly
Take a moment to reflect on the fact that Messier didn’t have a clue about M74’s true nature. Lurking inside the bright core is a quiescent black hole, and the misty light surrounding it is not at all like a morning fog — it’s the output of billions of stars shining at a staggering distance of 30 million light-years. We’re fortunate to live at a time when, for the most part, we can understand what we’re viewing.

A cometary interlude
Coincidentally, Comet C/2005 E2 (McNaught) floats just a few degrees from M74. Because you need to use the brighter stars of Aries as a starting point anyway, give the comet a look. Forget the marathon for 5 minutes, and experience a true Messier moment by observing a comet. At 10th magnitude, Comet McNaught will appear somewhat similar to the core of M74. You should see the comet as an almost stellar point, called the false nucleus, cocooned in a pale shroud of sunlit dust.

Whoa, look at the time! Better line up your next object and get hopping. If you have a go-to telescope, take advantage of this modern technology to locate each Messier object quickly. That way, you can return home with pages of comparative notes instead of a messy sheet littered with a bunch of check marks.

The planets

March gradually brings springtime weather to most of the United States. The later sunsets begin to catch up with Mercury as its elongation from the Sun rapidly diminishes. During the first week of March, you can find the innermost planet low in the west shortly after sunset. It continues its fine display that began in early February. Mars remains among the stars of Taurus the Bull; while in the eastern sky, Saturn climbs higher, ready for some fine evening viewing with telescopes.

You’ll want to spy Mercury early this month because it drops out of sight by March 6. On the 1st, the planet shines at magnitude 0.3 and lies 12° below a slender crescent Moon. Through a telescope, you can compare the Moon’s 6-percent illumination to Mercury’s thicker crescent, now about one-quarter lit. However, Mercury’s crescent wanes each day while the Moon’s waxes.

On March 2, for example, the lunar crescent has grown to 12-percent lit, compared with Mercury’s 19 percent. After March 4, when Mercury sets an hour after the Sun and shines at 2nd magnitude, the planet becomes hard to spot.

Mars, the Moon, and M45
Mars slides north of Aldebaran in Taurus this month, giving the Bull a pair of ruddy eyes. The Moon joins the scene March 5.
Astronomy: Roen Kelly
Mercury slides between the Sun and Earth March 11, then re-emerges in the morning sky during the month’s final week. This will be an unimpressive appearance, however. Mercury remains fainter than magnitude 0.8 until March 27, when a thin crescent Moon lies 5° south of the planet. The fast approaching twilight makes the Moon difficult to spot unless you have a clear and unobstructed eastern horizon. Mercury rises an hour after Venus and hugs the horizon until becoming lost in the dawn glow.

Taurus the Bull looks like it has two eyes this month. Aldebaran, the constellation’s brightest star and traditionally the eye of the Bull, shares the assignment with Mars. The Red Planet appears prominent 7° north of Aldebaran. Both objects shine at magnitude 0.8 in early March, although Mars fades by half a magnitude during the month.

Watch the sky March 5, when the crescent Moon lies between Mars and the Pleiades star cluster (M45). Mars continues to wander eastward across Taurus and, by the 31st, lies between the two stars marking the Bull’s horns, Beta (β) and Zeta (ζ) Tauri.

Telescopically, Mars is far past its best. The disk spans a mere 6″, too small for most scopes to show much detail, especially under the typically turbulent springtime skies. Its appearance as a bright “star,” however, will continue for several weeks.

Saturn has a prime location for evening viewing. An hour after sunset, it lies high in the southeast. The ringed planet shines at magnitude 0.0 and stands out among the faint stars of Cancer the Crab. Saturn passed opposition in late January, so it remains close to its best during March.

On the 10th, the waxing gibbous Moon serves as a guide to finding Saturn. In the early evening, look for the bright, starlike object 5° right of the Moon. A view through binoculars reveals the Beehive star cluster (M44) shimmering 2° east of the planet. Saturn’s motion carries it to a point 3° west of M44 by March 31. The planet halts its retrograde motion against the stars in early April and returns to direct motion, which will bring it south of M44 in June.

The best telescopic targets in this planet’s system, after the spectacular, 44″-diameter rings, are Saturn’s numerous moons. The moons dance a continuous waltz around the planet. Try to identify which one is which. This rewarding challenge takes on an added significance thanks to our newfound knowledge of the moons garnered by the Cassini spacecraft.

Dione’s batterred terrain stands out against Saturn’s cloud tops in this Cassini image.
Saturn in March 2006
You can spy Dione, and half a dozen other saturnian moons, through a 6-inch or larger scope with good optics.
Astronomy: Roen Kelly
Twice each month, Titan makes a complete orbit of the planet. Saturn’s largest moon is easy to see because it glows brightly at magnitude 8.4. Titan lies north of Saturn March 5 and 21, and south of the planet March 13 and 29. A much dimmer moon, Iapetus, lies near Titan March 29. Iapetus changes brightness as it turns its dark or light side toward us. At greatest western elongation, the moon appears relatively bright, at magnitude 10.1. This occurs in the second week of March. Even in a small telescope, you should see Iapetus easily to Saturn’s west. During the latter half of March, the moon dims slowly. See how long you can track it.

Other moderately bright moons lie closer to Saturn than Titan and Iapetus. Tethys, Dione, and Rhea each glow at 10th magnitude. The icy world Enceladus poses more of a challenge by glowing at magnitude 11.8. It lies close to the bright rings and skips around Saturn in less than a day and a half.

Giant Jupiter rises before midnight but doesn’t offer its best views until it climbs well above the horizon in the early morning hours. It stands 30° high in the southeast around 3 A.M. local time in early March, and by 1 A.M. late in the month. Later in the morning, you also can spot Antares, Scorpius’ brightest star, rising well to Jupiter’s lower left. The planet shines at magnitude –2.3 and dominates the rather dim constellation Libra the Scales. Because Jupiter lies at a southerly declination, observers at mid-northern latitudes won’t see it climb higher than about 40° all year.

Unlike Saturn, Jupiter’s disk brims with features that small telescopes — combined with a patient observer — can show. Jupiter’s large, 41″-diameter disk also helps. Obvious at first glance are two dark belts that run on either side of Jupiter’s equator. These are the North and South Equatorial Belts (NEB and SEB).

Jupiter’s other features are more subdued and often require a trick to view. The trick is to keep watching the planet for an extended period — which gives time for your eye to adapt to momentary improvements in “seeing.” Seeing describes the steadiness of the air, from your telescope to the edge of Earth’s atmosphere. Turbulence is the enemy of observers, yet moments of steady seeing occur frequently. Jupiter’s cloud tops reveal astonishing detail during these fleeting moments, so make the most of them.

Other observable dark features include the North and South Temperate Belts (NTB and STB). The South Tropical Zone lies between the SEB and the STB. The Great Red Spot resides in this zone and indents into the southern edge of the SEB. The spot’s current pale salmon-pink color makes it a subtle feature in the eyepiece.

Jupiter rotates in less than 10 hours, so new features appear each hour. Tracking features day after day is the best way to become familiar with the giant planet’s appearance.

Venus, March 25
Venus climbs highest in the morning sky during March, when it reaches its peak for this predawn apparition.
Astronomy: Roen Kelly
If the idea of standing out in the cold for extended periods doesn’t appeal to you, technology can come to your aid. Using a webcam, you can capture Jupiter through a telescope at 30 frames every second — enough to have dozens of frames that freeze the air’s turbulent motion and allow those random moments of great seeing to be captured forever.

Clever stacking software, such as the freeware Registax, optimizes the images to save only those frames that show sharp detail on the planet’s disk. Store no more than 2 minutes of video at a time because Jupiter’s fast rotation will start to blur details. Tedious pencil sketches at a cold eyepiece can now be replaced with endless happy hours processing images at a warm computer screen.

About 2 hours before the Sun rises, Venus pokes above the east-southeastern horizon. The planet shines at magnitude –4.4, making it the brightest point of light in the sky.

Venus’ telescopic appearance changes quickly during March. On the 1st, the planet’s disk measures 34″ across and appears 35-percent lit. By month’s end, it spans 23″ and looks a shade over half-lit. A waning crescent Moon passes to the right of the “morning star” March 25.

Mainly of academic interest is Neptune’s location 2° south of Venus March 26. Neptune’s dim, 8th-magnitude globe will be a challenge to see because of its low altitude and the rapidly advancing twilight.

Meteors and moons
Eclipse path
Darkness comes at midday March 29 to those along a narrow path that crosses Africa and Asia.
Astronomy: Roen Kelly
A totally grand eclipse
A list of nature’s most spectacular events would have to include a total solar eclipse. On March 29, observers can see more than 4 minutes of totality, the longest duration until July 2009.

The path of totality begins on Brazil’s coast. After crossing the Atlantic, the track traverses northern Africa, the eastern Mediterranean, and parts of Asia before ending in Siberia.

The highlights of any eclipse come just before, during, and after totality. Look for Baily’s beads as the last rays of sunlight peek through lunar valleys. The diamond ring is the final glint of this light. During totality, watch for reddish prominences and the ethereal corona. After totality, the diamond ring and Baily’s beads appear once more. To avoid blindness, view the partial phases only indirectly or with a proper solar filter.

A dusty solar system
No significant meteor shower takes place during March. The general background of sporadic meteors runs about 7 per hour, with occasional fireballs.

Although you won’t see much interplanetary dust burning up in Earth’s atmosphere, March evenings are prime time for viewing sunlight reflecting off dust in the inner solar system. This faint glow, called the zodiacal light, lies in the plane of Earth’s orbit, so it follows the constellations of the zodiac. Look for the zodiacal light after twilight completely fades away. You’ll see it only under the darkest sky, and low humidity increases its visibility.

Lunar crater Albategnius
Lunar crater Albategnius suffered many hits over billions of years but none bigger than the one that gouged out crater Klein.
Consolidated Lunar Atlas (LPI / UA)
Eye on Albategnius
Lying in the ancient highlands of the Moon’s southern hemisphere, Albategnius shows its age. The 85-mile-wide crater sits east of Mare Nubium, not far from the better known trio of Ptolemaeus, Alphonsus, and Arzachel. The crater’s western side sports a more recent crater: Klein, which measures 27 miles across. Many smaller craters have reshaped Albategnius’ northern wall.

Note the almost polygonal shape of Albategnius’ northeastern, northwestern, and western walls. This could reflect a fault system underlying the entire region. Many pits and a pronounced central peak mar the crater’s otherwise smooth floor. Several linear scars cross this region of the Moon, apparently radiating from the huge Mare Imbrium basin. These scars form an almost permanent record of a huge impact in the Moon’s distant past. The Sun rises over Albategnius near First Quarter phase March 6.

Comets and asteroids

A possible bright comet
The only thing predictable about comets is that they are unpredictable. That wisdom hit home with the appearance of Comet Kohoutek in the 1970s. And it certainly applies to Comet 73P/Schwassmann-Wachmann 3. This could be its last trip through the inner solar system. In 1995, the comet’s nucleus split as it rounded the Sun, just inside Earth’s orbit. Then, during the comet’s most recent return in early 2001, astronomers observed the three biggest components (B, C, and E). They were much brighter than predicted, probably because the breakup exposed fresh ice to sunlight.
Comet 73P
A bright visitor could light up the spring sky, but no one knows how bright Comet 73P/Schwassmann-Wachmann 3 will cecome. This month, it passes south of the bright star Arcturus.
Astronomy: Roen Kelly
This year, many astronomers think component C will be the only observed survivor. How bright will it get? Some comet experts predict it will peak near 7th magnitude, making it a nice binocular object. Others think the fragment will flare like other comets have done, and perhaps reach 1st or 2nd magnitude. That would make it an easy target for the unaided eye. The possibility also remains that it might dissolve into a low-contrast cloud that’s all but invisible to comet-watchers.

At the end of March, when the Moon is out of the late evening sky, Schwassmann-Wachmann 3 moves slowly near Arcturus above the eastern horizon. If we’re lucky and the nucleus is active, it will glow around 9th magnitude. This is within range of a small scope from a dark site. Otherwise, it might be a 13th-magnitude diffuse blob, challenging in even a 16-inch scope.

The positions shown on the chart below may be off slightly because the forces that caused the comet to break up may also delay its return.

A pair of German astronomers — Arnold Schwassmann and Arno Wachmann — discovered this comet May 2, 1930, in the course of a photographic search for asteroids. It appeared as a diffuse, 9.5-magnitude glow. Dust trails from the comet produced a shower of 60 to 70 meteors per hour June 9/10, 1930. This was anticipated because of the comet’s close pass to Earth. Unfortunately, dust-trail models predict Earth will not pass through a dense trail this June, despite the parent comet’s close passage.

Asteroid Vesta
Asteroid Vesta lies near Epsilon (ε) Gem, which makes an excellent guide to the 7th-magnitude minor planet.
Astronomy: Roen Kelly
Reliable rock
With a few notable exceptions, asteroids lead much simpler lives than comets. The third largest in the asteroid belt, Vesta, spans 320 miles and is slightly out of round. It reflects about 35 percent of the light that falls on it, which makes it the brightest asteroid whenever it approaches Earth.

Now that Earth is pulling away from Vesta, the asteroid fades from magnitude 7.4 to 7.8 during March. This is well within reach of a small scope, an excellent instrument for finding the asteroid. Apart from four or five background stars near Epsilon (ε) Geminorum, Vesta is the brightest object in the field. Make a quick sketch on one night, then come back a couple of nights later to confirm that it moved. By month’s end, the asteroid lies near a trio of similarly bright stars.

Tracking asteroids this month will give you practice for August, when three of these flying mountains hit their peaks in the same area of sky as the gas-giant planet Neptune.

Martin Ratcliffe is former president of the International Planetarium Society. Alister Ling is a meteorologist for Environment Canada.