May 15, 2012: Something strange is about to happen to the shadows beneath your feet.
On Sunday, May 20th, the Moon will pass in front of the sun, transforming sunbeams across the Pacific side of Earth into fat crescents and thin rings of light.1
It's an annular solar eclipse, in which the Moon will cover as much as 94% of the sun. Hundreds of millions of people will be able to witness the event. The eclipse zone stretches from southeast Asia across the Pacific Ocean to western parts of North America: animated eclipse map.
Crescent sunbeams dapple the ground beneath a palm tree during an annular eclipse in January 2010. The picture was taken by Stephan Heinsius on the Indian Ocean atoll island of Ellaidhoo, Maldives. [more] [video]
In the United States, the eclipse begins around 5:30 pm PDT. For the next two hours, a Moon-shaped portion of the sun will go into hiding. Greatest coverage occurs around 6:30 pm PDT.
Because some of the sun is always exposed during the eclipse, ambient daylight won't seem much different than usual. Instead, the event will reveal itself in the shadows. Look on the ground beneath leafy trees for crescent-shaped sunbeams and rings of light.
A "ring of fire" over China in 2010.
Near the center-line of the eclipse, observers will experience something special: the "ring of fire." As the Moon crosses the sun dead-center, a circular strip or annulus of sunlight will completely surround the dark lunar disk. Visually, the sun has a big black hole in the middle.
The "path of annularity" where this occurs is only about 200 miles wide, but it stretches almost halfway around the world passing many population centers en route: Tokyo, Japan; Medford, Oregon; Chico, California; Reno, Nevada; Albuquerque, New Mexico, and Lubbock, Texas. In those locations the ring of fire phenomenon will be visible for as much as 4 and a half minutes.
"The ring of sunlight during annularity is blindingly bright," cautions NASA's leading eclipse expert Fred Espenak of the Goddard Space Flight Center. "Even though most of the Sun's disk will be covered, you still need to use a solar filter or some type of projection technique. A #14 welder's glass is a good choice. There are also many commercially-available solar filters."
The path of annularity cuts across the continental United States near sunset on May 20, 2012. An interactive map is also available: click here. See also the ScienceCast video.
Many astronomy clubs will have solar-filtered telescopes set up for public viewing. Through the eyepiece of such an instrument, you can see the mountainous lunar limb gliding by dark sunspots and fiery prominences. It's a beautiful sight. Be absolutely sure, however, that any telescope you look through is properly filtered. Magnified sunlight can cause serious eye damage even during an eclipse.
A safe and fun way to observe the eclipse is to use your own body as a solar projector. For example, try criss-crossing your fingers waffle-style. Rays of light beaming through the gaps will have the same shape as the eclipsed sun.
Or just stand under that tree. The sight of a thousand ring-shaped sunbeams swaying back and forth on a grassy lawn or sidewalk is unforgettable.
Skywatchers in East Asia and the western United States should circle this upcoming Sunday on their calendars. That's when a solar eclipse will block out most of the sun, leaving a spectacular "ring of fire" shining in the sky for observers located along the eclipse's path.
The event is what's known as an annular solar eclipse — from the Latin "annulus," meaning "little ring" — and its full glory should be visible from much of Asia, the Pacific region and some of western North America, weather permitting. At its peak, the eclipse will block about 94 percent of the sun's light.
Other parts of the United States and Canada will still see a partial solar eclipse, without being treated to the ring of fire effect, though the East Coast will miss the event since the sun will have set before it begins.
The eclipse will occur in the late afternoon or early evening of May 20 throughout North America, and May 21 for observers in Asia.
Solar eclipses occur when the moon comes between Earth and the sun, casting a shadow on our planet. When the moon lines up perfectly with the sun and blots out all of its light, the result is a total eclipse.
Annular eclipses are similar to total eclipses in that the moon lines up with the sun dead-on. But in this case, the moon is close to apogee — the farthest point from Earth in its elliptical orbit around our planet — so it's a smidge too small in the sky to cover the solar disk completely. As a result, a ring of bright sunlight will still blaze around the moon's circumference.
Like other types of solar eclipses, annular eclipses are spectacular but potentially dangerous skywatching events. Care must be taken to observe them properly, or serious and permanent eye damage — including blindness — could result.
Warning: Never look directly at the sun, either with the naked eye or through telescopes or binoculars without the proper filters.
To safely observe the May 20 annular eclipse, you can buy special solar filters to fit over your equipment, or No. 14 welder's glass to wear over your eyes. Do NOT use standard sunglasses or any kind of homemade sun-shading contraption.
The safest and simplest technique is perhaps to watch the eclipse indirectly with the solar projection method. Use your telescope, or one side of your binoculars, to project a magnified image of the sun’s disk onto a shaded white piece of cardboard.
The image on the cardboard will be safe to view andphotograph. Be sure to cover the telescope's finder scope or the unused half of the binoculars, however, and don't let anybody look through them.
And if you snap any good eclipse photos that you'd like to be considered for use in a story or gallery, send them to Space.com managing editor Tariq Malik at email@example.com.
You can follow Space.com senior writer Mike Wall on Twitter: @michaeldwall. Follow Space.com for the latest in space science and exploration news on Twitter @Spacedotcom and on Facebook.
Hinode / XRT
On Jan. 4, 2011, the moon passed in front of the sun in a partial solar eclipse — as seen from parts of Earth. Here, the joint Japanese-American Hinode satellite captured the breathtaking event from space. The view created what's called an annular solar eclipse.
The following is a brief list of sources for mylar and/or glass filters specifically designed for safe solar viewing with or without a telescope. The list is not meant to be exhaustive, but is simply a representative sample of sources for solar filters currently available in the United States. For additional sources, see advertisements in Astronomy and/or Sky & Telescope magazines. The inclusion of any source on this list does not imply an endorsement of that source by either of the authors or NASA.
ABELexpress - Astronomy Division, 230-Y E. Main St., Carnegie, PA 15106 - (412) 279-0672
Celestron International, 2835 Columbia St., Torrance, CA 90503 - (310) 328-9560