Posted on 05/27/2003 9:55:13 AM PDT by NYer
A partial eclipse of the Sun surrounded by strange circumstances is on tap for Saturday, May 31 and will be visible in parts of North America, Europe and the Middle East. The event could be quite spectacular at sunrise in Europe, especially in the United Kingdom. Looking directly at the Sun is dangerous, so proper viewing techniques (below) are necessary. The most impressive aspect of the event will be an annular, or ring eclipse, so named because the Moon’s disk will be too small to completely cover the Sun’s disk. The result is a ring of fire surrounding the black circle of the Moon. It's like a dull penny sitting atop a shiny nickel. Annular eclipses can occur because the Moon's orbit around Earth is not quite a circle. When the Moon is closer to Earth than average, a total solar eclipse can occur. When it is farther than average, an annular eclipse can result. The annular eclipse will be visible across a sparsely populated swath of Earth from Scotland to the Canadian Arctic. The extreme northern track of the Moon's shadow will likely make this one of the most unusual solar eclipses that will occur in the 21st century.
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Here's why:
The antumbra or negative shadow of the Moon – from where the annular phase of eclipse is visible – will strike the Earth at a very oblique angle. In fact, the shadow will actually pass above the North Pole and a bit beyond it before it finally makes contact with the Earth’s surface. As a result of this extraordinary geometry, the antumbra appears to graze the Earth’s surface resulting in a broad, semicircular region that will experience the "ring of fire" effect.
Also, because of this unusual circumstance, instead of moving in a typical west-to-east fashion, as is the case with most solar eclipses, the shadow’s movement will actually run in reverse – from east to west.
Where to see a partial eclipse
Outside of the zone of the annular eclipse, most of Europe, the Middle East, central and northern Asia and northwestern sections of North America will be underneath the Moon’s outer shadow, or penumbra, and will see a partial eclipse. The effect is that of the Moon taking a bite out of the Sun.
The closer one is positioned to the region of visibility of the annular eclipse, the larger the eclipse. Those living in northern and eastern sections of Europe will be in position to see more than 80 percent of the Sun’s diameter eclipsed at, or soon after sunrise. Across parts of central Europe, which includes Ireland, much of England and France, Switzerland and Italy, the peak of the eclipse will have already occurred when the Sun finally comes up above the horizon – nonetheless still making for a most unusual sunrise!
Interestingly, the partial eclipse will also be visible across all of Alaska as well as a swath of northern and western Canada. Depending on where you are located, you might expect to see anywhere from about 40 to 80 percent coverage.
However, adding to the oddities associated with this eclipse, for these "Al-Can localities," since the Moon’s penumbral shadow falls to the east of the International Date Line, local clocks will be set to the previous day: Friday, May 30. Moreover, for these particular locations the eclipse will be occurring not at sunrise, but around the time of sunset.
Where to see the annular eclipse
The region from where the annular phase will be visible takes on an outline resembling a peculiar "D" shape that spans nearly 750 miles (1,200 kilometers), broader than any eclipse path in this century. The antumbra itself, thanks to the grazing angle it makes from the low Sun, projects onto the Earth’s surface as an extremely elongated ellipse. The broad area of visibility includes northern Scotland, encompasses all of Iceland before crossing into central Greenland, before ending in Baffin Bay, Canada.
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The antumbral shadow will sweep over the Earth in a little under 47 minutes, beginning at 3:45 GMT. The actual axis of the shadow will ever-so-briefly touch down on the Earth for just 12 minutes, from 4:02 to 4:14 GMT, tracing a short semicircular path that starts and ends at local sunrise. This is in stark contrast to most other total or annular eclipses, whose tracks usually begin at sunrise and take a course in a general easterly direction, ending a few hours later at sunset.
The annular eclipse will begin somewhere on Rannoch Moor in the midst of the Grampian Mountains of the Scottish highlands. This is about 62 miles (100 kilometers) north of Glasgow. Notable locations in Scotland that will see (local weather conditions permitting) the Sun appearing as a glowing ring at or shortly after sunrise include the Northwest Highlands, Loch Ness, the Isle of Lewis (Outer Hebrides), the Orkney and Shetland Islands.
Several minutes later, as the antumbral shadow moves in a northwesterly direction, the Faeroe Islands (which belong to Denmark) will experience the annular eclipse. Less than ten minutes later, the shadow will envelop Iceland. From the capital city of Reykjavik, the annular eclipse will last 3 minutes 36 seconds.
But prospects for clear skies here are not at all good. According to Jay Anderson, a meteorologist with Environment Canada, "The Icelandic low (about 600 miles or 1,000 kilometers to the southwest) is the source of a frequent and endless supply of weather systems that move past the island, each one bringing its own retinue of cloud and precipitation; overcast skies with rain or snow are the norm."
Yet, even if skies dawn perfectly clear over Reykjavik, many of its 106,000 inhabitants may still miss the low-altitude spectacle because of mountains that could block their view toward the northeast.
Continuing in a northwest direction, the eclipse reaches its maximum about 120 miles (200 kilometers) beyond Iceland in the Denmark Strait at 4:08 GMT. Here, the annular eclipse will last 3 minutes 37 seconds, with the Sun standing a mere 3º above the horizon. The shadow then cuts across the center of the sparsely inhabited island of Greenland, before finally leaving the Earth over Canada’s Baffin Bay.
Looking at the Sun without proper eye protection is dangerous.
Unlike a total eclipse of the Sun, concentrating its excitement into a few fleeting minutes, a partial eclipse can be watched in a relaxed fashion from wherever one happens to be. Observations can be made with the naked eye, binoculars, or telescopes of any size. However, looking at the Sun is harmful to your eyes at anytime, partial eclipse or no. Most people are under the mistaken impression that when a solar eclipse is in progress that there is something especially insidious about the Sun’s light.
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But the true danger that an eclipse poses is simply that it may induce people to stare at the Sun, something they wouldn’t normally do. The result can be "eclipse blindness," a serious eye injury that has been recognized at least since the early 1900’s. About half of the reported victims of eclipse blindness recover their precious quality of eyesight after a few days or weeks. The other half carries a permanent blurry or blind spot at the center of their vision for the rest of their lives.
Fortunately, public warnings by news media have vastly reduced solar eye injuries at eclipses in the last few decades. After the solar eclipse that crossed the United States on March 7, 1970, no fewer than 245 cases of retinal injury were reported. Of these people, 55 percent suffered permanent impairment of vision.
In contrast, after the solar eclipse of May 30, 1984, Sky & Telescope magazine was able to locate only three cases of eclipse blindness in the entire United States. During any direct observation of the eclipse, your eye or must be protected by dense filters from the intense light and heat of the focused solar rays.
By far, the safest way to view a solar eclipse is to construct a "pinhole camera." A pinhole or small opening is used to form an image of the Sun on a screen placed about three feet behind the opening. Binoculars or a small telescope mounted on a tripod can also be used to project a magnified image of the Sun onto a white card. Just be sure not to look through the binoculars or telescope when they are pointed toward the Sun!
A variation on the pinhole theme is the "pinhole mirror." Cover a pocket-mirror with a piece of paper that has a ¼-inch hole punched in it. Open a Sun-facing window and place the covered mirror on the sunlit sill so it reflects a disk of light onto the far wall inside. The disk of light is an image of the Sun’s face.
The farther away from the wall is the better; the image will be only one inch across for every 9 feet from the mirror. Modeling clay works well to hold the mirror in place. Experiment with different-sized holes in the paper. Again, a large hole makes the image bright, but fuzzy, and a small one makes it dim but sharp. Darken the room as much as possible. Be sure to try this out beforehand to make sure the mirror’s optical quality is good enough to project a clean, round image.
Of course, don’t let anyone look at the Sun in the mirror.
Acceptable filters for unaided visual solar observations include aluminized Mylar. Some astronomy dealers carry Mylar filter material specially designed for solar observing.
Also acceptable is shade 14 arc-welder’s glass, available for just a few of dollars at welding supply shops. It also used to be widely advertised that two layers of fully exposed and developed black-and-white negative film was safe. This is still true but only if the film contains an emulsion of silver particles. But beware: some black-and-white films now use black dye, which is no longer safe.
It is always a good idea to test your filters and/or observing techniques before eclipse day.
Unacceptable filters include sunglasses, color film negatives, black-and-white film that contains no silver, photographic neutral-density filters, and polarizing filters. Although these materials have very low visible-light transmittance levels, they transmit an unacceptably high level of near-infrared radiation that can cause a thermal retinal burn. The fact that the Sun appears dim, or that you feel no discomfort when looking at the Sun through the filter, is no guarantee that your eyes are safe.
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The next solar eclipse is scheduled to occur later this year on Sunday, Nov. 23. It will be a total eclipse less than two minutes long that will sweep across parts of Antarctica.
Next year there will be two solar eclipses, both only partial.
On April 19, 2004, viewers in the southern third of Africa will be able to see up to about 50 percent of the Sun eclipsed. The maximum of 73.5 percent coverage unfortunately lies inaccessibly close to the Antarctic coast, thousands of kilometers south of the Cape of Good Hope.
On Oct. 13, 2004 a large partial solar eclipse will take over western Alaska, again at sunset. Near the town of Kenai (southwest of Anchorage), nearly 93 percent of the Sun will be eclipsed.
How about you?
Nah, he won't ban it, he'll just tax you for the privilege - to cover the additional medical costs, of course.
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Annular eclipse
Partial eclipse 
