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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!
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.
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.
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.
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.
"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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June 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.
Right:
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.
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