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Eclipse Safari

On Thursday, June 21st, the Moon's shadow will race across southern Africa for the only total solar eclipse of 2001. The display will delight some creatures and put others to sleep.

NASA
Marshall Space Flight Center

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see captionJune 19, 2001 -- This Thursday something strange will happen in parts of southern Africa. For nearly four minutes a curious twilight will descend where the afternoon Sun normally beats down bright and hot. Nocturnal animals like bats, owls and astronomers will suddenly become active as the New Moon passes in front of the Sun blocking out our star's fiery disk.

It's the first total solar eclipse of the new millennium and the only one this year.

Above: With the bright disk of the Sun covered, the faint corona becomes visible to the naked eye. Image credit: Fred Espenak.

Thousands of eclipse chasers are making the safari to Africa to see the show. Hotels along the path of totality --a 127-km wide corridor stretching from Angola to Mozambique-- are filled to the brim, while local shops are doing a brisk trade in commemorative T-shirts and Sun filters. It's a big event!

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Thursday's eclipse will begin in the sparsely populated south Atlantic Ocean -- not a convenient location for sky watchers. Fortunately, the Moon's shadow won't remain there. Racing eastward at 0.63 km/s (1410 mph), it will make landfall around local noon in war-torn Angola. A safer viewing site will be Lusaka, the capital of Zambia, where scientists from NASA have gathered to study the Sun. In Lusaka the Moon will completely cover the Sun at 3:11 pm local time (6:11 am PDT), and totality will last for 3 minutes and 14 seconds. If you have a high speed internet connection you can view a live webcast from Zambia courtesy of NASA and the San Francisco Exploratorium.

During the precious minutes of totality, our star's wispy corona will spring into view. This faint layer of ionized gas extends more than 13 million kilometers from the Sun's visible surface out into space. During an eclipse it stretches across the sky, shimmering hypnotically. It's an unforgettable sight -- one that turns many first time eclipse watchers into dedicated lifetime "eclipse chasers."

Below: The red strip indicates the path of totality for Thursday's eclipse. Sky watchers inside the yellow lines will experience a partial eclipse. Image courtesy MrEclipse.com.

see captionThe corona is not only beautiful, it's mysterious, too. One thing that puzzles scientists about the corona is that it's actually much hotter than the surface of the Sun itself -- about 1,000 times hotter! The corona can reach up to 4 million degrees Celsius, while the surface of the Sun is "only" 6,000 °C. 

What could account for the corona's extreme temperature?

Jay Pasachoff, Field Memorial professor of astronomy at Williams College in Williamstown, Massachusetts, will conduct experiments during Thursday's eclipse in Lusaka to test one of the candidate hypotheses: Astronomers have long known that the corona is permeated with the Sun's twisted magnetic field. Pasachoff suspects that vibrating magnetic field lines, which may oscillate as rapidly as once per second, transmit energy into the coronal gas and inflate its temperature.

"There's a great boiling effect, a convective turbulence, in the upper one-third of the Sun," explains Pasachoff. Turbulent motions near the Sun's surface launch magnetic waves (called Alfven waves) into the corona where they "break" --like a wave on a beach-- and convert wave energy into thermal energy. Do such waves carry enough power to warm the corona to millions of degrees? That's what Pasachoff and his colleagues hope to find out. During the eclipse they will monitor green-colored light emitted by highly ionized iron atoms in the hot corona. Fluctuations in the intensity of the so-called "coronal green line" could reveal the telltale magnetic vibrations. Measuring the strength of such oscillations would be a major step toward unraveling the mystery of the corona's extreme temperature, says Pasachoff.

see captionWhy do solar eclipses occur?

When the New Moon passes directly between the Sun and Earth, it casts a shadow on our planet, just as a baseball does if held above the ground in direct sunlight. That, in a nutshell, is what causes a solar eclipse.

There's a New Moon every month, so why don't we have a solar eclipse every month, too? The answer is that the Moon's orbit is slightly tilted compared to the Earth's orbit around the Sun -- by 5 degrees, to be exact. So when the Moon comes between the Earth and the Sun, it's usually a little above or below the plane of Earth's orbit, and its shadow misses the Earth. Only occasionally -- about twice a year -- can eclipses occur.

Above: Click to view a Quicktime animation of the Moon's shadow sweeping across Earth during a total solar eclipse. Credit: Digital Radiance.

As any seasoned eclipse watcher can testify, a solar eclipse is not only an astronomical event -- it's a biological one, too.

Adding to a sense of the surreal during a total eclipse, many creatures begin to act strangely when the sky turns dark, apparently disoriented by nighttime's sudden and unexpected visit.

"Diurnal animals (those that are awake during the day) do what they usually do at night: sleep!" says Charlotte Vermeulen, a biologist at the Artis Zoo in Amsterdam, which experienced a 98 percent partial eclipse in August 1999 during which many people came to the zoo to see the reactions of the animals. "Dragonflies hide under a leaf, ants return to their nest, sheep walk back to their sleeping place, cattle egrets return to their nocturnal roost, diurnal grasshoppers chirp more slowly and then stop."

Below: A bird in flight during the spring 1995 annular eclipse in Ecuador. Photo by Olivier Staiger.

"Nocturnal animals become active: owls hoot, bats fly, blackbirds sing like they do in the early morning, cocks crow, nocturnal grasshoppers start chirping, and so on," Vermeulen says. "One very remarkable observation: 12 chimpanzees in Atlanta were observed to climb to a higher perch, look at the Sun, and point at the Sun during totality! Almost too good to be true, but this observation was done at a primate observation center and published in a sound scientific magazine."

Vermeulen will be giving a presentation about animal responses to solar eclipses at Artis Zoo preceding Thursday's eclipse, followed by a live viewing of the eclipse via webcast.

The Web will also be used to let people all over the world participate real-time in a simple scientific experiment that will be conducted in Lusaka, Zambia, in the path of the total eclipse.

The sudden loss of direct sunlight during an eclipse causes air temperatures to dip slightly, along with a host of other weather effects. This year, anyone with Internet access can view this change in temperature in near real-time by pointing their browser to SpaceWeather.com.

The website will feature temperature measurements taken by a NASA scientist on location in Africa, as well as near real-time digital photos of the eclipse.

"It's basically just a little experiment to provide some data to students," says Mitzi Adams, who will be in Lusaka operating the temperature sensor and uploading the data to the Web. 

see captionRight: This animation shows how the Moon's shadow will fall on the Earth during Thursday's eclipse. Notice how the shadow consists of a lighter region -- called the "penumbra" -- and a darker spot -- called the "umbra." Only where the dark spot falls does a total eclipse occur. The lighter part of the shadow produces only a partial eclipse. Courtesy Andrew Sinclair.

"It's very simple: We'll take a reading once every minute or so, and we'll look at how the temperature varies from about 30 minutes before to 30 minutes after totality," says Adams, an astrophysicist with NASA's Marshall Space Flight Center in Huntsville, Alabama.

In addition to the data and pictures on SpaceWeather.com, Adams will host a conference call during the eclipse that will include Girl Scout groups in Huntsville and Atlanta and Air Force ROTC instructors in Alabama. The tele-conference will allow participants to look at the data and pictures and ask Adams questions, all while the eclipse is occurring.

Adams says the motivation for creating this "virtual eclipse" is to inspire students and to help get them involved in doing science.

"I really am interested in trying to encourage girls of all ages to become interested in astronomy and sciences in general," she says. "Just the awe of being involved in an eclipse -- I mean it's an incredible experience -- I think it can be a major hook for getting and retaining interest in astronomy and science."

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Web Links

June 21 total solar eclipse -- information and links about Thursday's eclipse, from NASA's Goddard Space Flight Center

Williams College expedition -- more information on Pasachoff's experiments for Thursday's eclipse

Solar eclipses -- general information

The right way to view a solar eclipse -- safety is important when viewing a solar eclipse. Looking directly at the Sun can make you go blind! Learn how to watch an eclipse safely with this webpage.

Effects during a total eclipse -- several interesting visual effects happen just before and after an eclipse

Solar eclipses of historical interest -- links to information about past eclipses with historical import

Solar eclipses were not always enjoyed -- before the real reason for eclipses was figured out, ancient peoples often feared them. Learn more about ancient beliefs surrounding eclipses here.


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