Total solar eclipse explained

A total eclipse of the sun is one of nature?s most spectacular and awe-inspiring sights. For sheer beauty and magnificence, perhaps no celestial phenomena can compare with it.

On Wednesday, Nov. 14, residents and visitors in Cairns, in Queensland, Australia, will witness the moon completely cover the sun for two minutes in the eastern sky an hour after local sunrise, provided the weather is clear (cloudy conditions could spoil the show). Because of the time zone difference, it will still be Tuesday afternoon (Nov. 13) in the United States during the total solar eclipse.

Cruise ships positioned farther east off the coast of New Caledonia and New Zealand will intercept the moon?s dark shadow, called the umbra, on the open waters of the South Pacific, giving passengers even longer durations of totality ? up to 2.5 and 3.5 minutes, respectively. The eclipse will begin at 3:35 p.m. ET (20:35 GMT) and last about 3.1 hours as the moon's shadow moves across Earth.

You can watch two live webcasts of the total solar eclipse here at SPACE.com beginning at 1 p.m. ET (18:00 GMT).

If you have never seen a total solar eclipse before, here?s a list of eclipse events you can expect to see during the event, in chronological order:

First contact: This is the moment when the moon first takes a barely perceptible "bite" on the western edge of the sun, marking the official start of the eclipse. [How Solar Eclipses Work (Infographic)]

In Cairns, this occurs right after sunrise at local time on Wednesday (afternoon ET on Nov. 13), with the sun a mere 2 degrees above the eastern horizon. (Your closed fist held at arm's length covers 10 degrees of the sky.)

Vanishing crescent sun: Over the course of nearly an hour, the initial notch on the solar disk grows bigger and bigger as the moon continues to cover more of the sun. As the solar disk is reduced to a slender, rapidly dwindling crescent, look for pinhole images of the solar crescent projected by tiny spaces in between the leaves of a tree or shrub. The crescents can be seen on the ground or on any light-colored material, such as your T-shirt or notepad.

Fading daylight: About 15 minutes before totality begins, with about 80 percent of the sun now blocked, you?ll notice a drop in ambient light. As the partial solar eclipse deepens, daylight fades very quickly and dramatically. Shadows cast by the sun also appear much sharper. As totality nears, the surroundings lose much of their color, and the landscape takes on an unearthly grayish blue cast. [Video: Watch Path of Nov. 13-14 Total Solar Eclipse]

Dropping temperature: As more and more of the sun gets covered up, you may start to feel a slight cooling in the air.

Approaching lunar shadow: The moon?s dark shadow, called the umbra, which has been racing along Earth?s surface at up to several thousand kilometers per hour, is now rapidly closing in on your observation site. With 15 minutes to go before totality, the shadow now looms over the western horizon like a distant gathering storm.

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Nature?s reaction: As day gradually turns to dusk, plants and animals usually behave as if night has fallen. Flowers close, birds stop singing, cows and chickens come home, and bats and nocturnal birds and fishes come out to feed. Soon everything becomes still and hushed in anticipation that something dramatic is about to happen.

Shadow bands: A few minutes before totality begins, the last rays of the sun are distorted by Earth?s turbulent atmosphere, producing wavy patterns of alternating light and dark bands that move quickly across the ground. (Many observers often miss this solar eclipse phenomenon since their attention is focused on the sun and not on the ground.) Shadow bands are notoriously difficult to photograph since they are faint and fast-moving. A white blanket or towel laid out on the ground will help you see (or videotape) them better.

Inner corona: Less than a minute before totality, you might be able to glimpse the brightest part of the sun?s outer atmosphere, called the corona, beginning to emerge. [Total Solar Eclipse of 2012 Explained (Gallery)]

Baily?s beads: These bright, rosary-like beads of sunlight ? named after British astronomer Francis Baily who first reported them during an eclipse in 1836 ? become visible up to 10 seconds or so before totality as the moon blocks the sun?s disk and sunlight continues to stream through deep valleys along the moon?s rugged edge.

Dazzling diamond ring: ?As the last traces of the sun?s disk is covered by the moon, a solitary bead of sunlight remains shining briefly, creating a spectacular "diamond-ring" effect. People start to cheer, whoop, clap and cry.

Prominences and the chromospheres: At the same time, the thin, neon-pink layer of the sun?s atmosphere, called the chromosphere, becomes visible on the sun?s eastern edge. Any solar prominences present will also be seen protruding from behind the rapidly encroaching black disk of the moon.

Second contact: This heralds the moment when the diamond ring is finally extinguished and the sun is fully obscured by the moon. Total eclipse begins. Simultaneously, the dark lunar shadow that has been growing in the west rushes in and engulfs everything. You are now standing in the shadow cast by themoon a quarter of a million miles away. The moon?s inky disk set against the sun?s pearly white corona appears like an eerie black hole in the sky.

In Cairns, second contact occurs at 6:39 a.m. local time, with the sun 14 degrees high in the sky.

Outer corona: During the brief period of totality, the full extent of the sun?s corona is displayed in all its glory. Take note of the solar prominences and the overall shape and size of the corona, which vary from eclipse to eclipse. Try to discern fine details in the corona?s structure ? such as long wispy streamers as well as delicate brushes, loops and arcs ? which are delineated by the sun?s powerful magnetic field.

Twilight colors and darkness: The daytime darkness during totality doesn?t really get as black as at night. It resembles more of a deep twilight. While the sky surrounding the eclipsed sun is dark, all along the horizon the sky remains bright, bathed in a vivid yellowish orange glow. It?s like being surrounded by a 360-degree sunset.

Planets and stars: The brightest planets and stars typically come out in the minutes leading to totality and remain visible throughout the total eclipse. On Nov. 14, Venus should be fairly easy to spot west of the eclipsed sun. Mercury to the east and Saturn in between Venus and the eclipsed sun might be more challenging. Keen-eyed observers can also try to glimpse the stars Arcturus to the north and Alpha Centauri to the south.

Temperature drop: If you have a thermometer in the shade, you can measure how much the ?temperature has decreased since first contact. Depending on the duration of totality and how high the sun is in the sky, the air temperature can dip by as much as 2 to 8 degrees Celsius (4 to 14 degrees Fahrenheit).

End of totality nears: You?ll know that the show is almost over when the western side of the corona begins to brighten, and the chromosphere and prominences become visible again.

Third contact: After a few minutes of totality, as the moon begins to uncover the sun, observers will see a single bead of sunlight burst forth in slow motion from behind a deep lunar valley, forming a magnificent diamond ring. The total eclipse is over, and another round of loud cheering and applause erupts from the crowd.

Over the next hour, the various stages of the eclipse repeat themselves, this time in reverse order and on the western side of the sun. The moon?s shadow races to the east as Baily?s beads reappear. The corona as well as the planets and stars fade from view.

Daylight returns very quickly, as if somebody had turned off the celestial dimmer switch. As the razor-thin sliver of the sun grows larger, shadow bands briefly come into view. Everything goes back to normal, including plants, animals and humans. The solar crescents continue to grow wider as the moon slowly moves away from the sun?s disk.

Fourth contact: At 7:40 a.m. local time, the moon leaves the sun?s disk completely as seen from Cairns. The last solar eclipse of 2012 is officially over. Time to celebrate!

Upcoming American eclipses
Skywatchers in the United States will get their chance to witness a total solar eclipse on Aug. 21, 2017. The eclipse track cuts across the country from Oregon to South Carolina, passing through several major cities, including Lincoln, Neb.; Kansas City and St. Louis, Mo.; Nashville, Tenn.; and Charleston, S.C. The greatest duration of totality ? 2 minutes 40 seconds ? takes place near Hopkinsville, Ky.

The last time a total solar eclipse was visible from the U.S. was July 11, 1991, from Hawaii?s Big Island. After 2017, the next one will not take place until April 8, 2024, when the eclipse path crosses Texas (duration of totality: 4.5 minutes) and heads up north to Maine (3.5 minutes).

Good luck and clear skies!

Editor's note: If you are in Australia or along the solar eclipse path and snap an amazing photo of Tuesday's total solar eclipse that you'd like to share for a possible story or image gallery, please send images, comments and location information to managing editor Tariq Malik at tmalik@space.com.

?? Imelda Joson and Edwin Aguirre are veteran eclipse chasers and photographers with 10 successful expeditions to date (eight totals and two annulars). Follow SPACE.com on Twitter@Spacedotcom. We're also on Facebook and Google+.

? 2012 Space.com. All rights reserved. More from Space.com.

Source: http://www.msnbc.msn.com/id/49805768/ns/technology_and_science-space/

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