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Where and how to see the eclipse

Reuters file

A "ring of fire" glows around the dark moon on Jan. 26, 2009, as seen from Bandar Lampung in Indonesia during an annular solar eclipse.

Eclipse-chasers have been known to plan their expeditions months or even years in advance, but if you can get to the western United States, there's still plenty of time to plan your party for this month's solar eclipse. If the skies are clear, all you have to do is look up — with the proper eye protection, of course.

The May 20 event won't be quite as spectacular as a total solar eclipse, but if you can make it to a 200-mile-wide strip of territory that extends from the Oregon-California coast to northwestern Texas, you just might see a rare "Ring of Fire" eclipse near sunset. And that zone of annularity runs through some of the most picturesque parts of the country, including the Grand Canyon and 32 other national parks.

Outside the strip, Westerners will see a partial solar eclipse for the first time in seven years.

"Think of Pac-Man taking a bite out of the sun," Jonathan Jarvis, director of the National Park Service, said in a news release. "That 'bite' will take out 55 to 80 percent of the disk of the sun, depending on where you are, and that's still a very special experience."

The park service has put together an interactive website that shows you where the eclipse will be visible, lists events tied to the eclipse and provides more online resources about the phenomenon. Don't dawdle over your travel plans: Some of the park events, such as a viewing session from New Mexico's Petroglyph National Monument, are already sold out.

This eclipse will be an international spectacle that's not to be missed. Over the course of three and a half hours, the moon will blot out at least part of the sun, as seen from earthly locales stretching from Southeast Asia through China and the Pacific to North America and Greenland. Because of the moon's position with relation to Earth, the lunar disk will never block the sun completely, but will leave at least an edge of the solar disk exposed.

Safety first
For that reason, it's important to use the proper protection when gazing at the eclipse, even during the "Ring of Fire" phase. You can buy safety glasses for less than a buck each from Telescopes.net, with all of the proceeds going to support Astronomers Without Borders. Eclipse shades are available as well from Rainbow Symphony and lots of other online vendors.

You can also put a solar filter on your telescope or binoculars — but regular sunglasses won't do the trick. The filters should be specially designed for solar viewing. Same goes for your camera: Unless you know what you're doing, taking a picture of the sun without the proper filter is a good way to ruin your point-and-shoot. NASA's top eclipse expert, Fred Espenak, offers a guide to photographing any kind of solar eclipse easily and safely.

National Park Service

A graphic shows U.S. national parks within the zone of annularity for the May 20 solar eclipse. A partial solar eclipse can be seen from parks outside the zone that are marked in orange. Click on the interactive map.

Another way to view the eclipse is to fashion a "pinhole camera" from a box, aluminum foil and a sheet of white paper — or even from just two squares of cardboard. This Exploratorium webpage shows you how. The simplest way to get a sense of the eclipse is to find a semi-shady spot and watch the circles of sunlight falling through tree leaves. During a partial eclipse, the circles will turn into half-moons or crescents. If the sun goes annular, you'll see bright rings on the ground.

If you're in the Western states, the best time to look will be in the late afternoon of the 20th. NASA has put a clickable map online that shows you when the different stages of the eclipse occur for the locality you click. One caveat: The times are listed as Universal Time, so you'll have to subtract seven hours for Pacific Daylight Time, six hours for Mountain Time, or five hours for Central Time.

Where to go
You can track eclipse visibility using the maps available from NASA or the National Park Service, but how do you pick just the right place? Paul Doherty, senior staff scientist for the Exploratorium in San Francisco, advises matching up the maps with places that are accessible and tend to have clear skies. Eclipser's Forecast Desk provides long-term projections of global sky conditions for the hard-core eclipse-chaser, and when you get within 48 hours of the event, the Clear Sky Chart can give you a better idea what to expect.

It's a good idea to scout out your location in advance if you can, and it's also a good idea to retain some flexibiliity in your itinerary, just in case you have to shift your base of operations to find a clear patch of sky. I'm planning to head for Crescent City, Calif., to see a close-to-sunset eclipse over the Pacific, but from what I've been hearing about the fogginess on the coast, it'd be prudent for me to check out some vantage points farther inland.

Make sure you've got good western exposure, though. "You don't want mountains to be in the way," Doherty said. The farther east you go, the later the eclipse occurs — and the closer the sun will be to the western horizon. Some observers have dubbed Albuquerque, N.M., as the prime urban spot for seeing this eclipse, but the "Ring of Fire" will flash there just before sunset. That means you'll need a clear line of sight to the far horizon.

Jan. 15, 2010: Astronomers believe a solar eclipse seen across Africa, Asia and the Indian Ocean may be the longest annular eclipse in more than 1,000 years. Msnbc.com's Dara Brown reports.

Hang onto those glasses
After the eclipse, you can put your sun-viewing glasses through another tryout during the transit of Venus on June 5. Over the course of several hours, the planet Venus will be visible as a tiny speck of black, making its way across the sun's disk for what Doherty calls a "micro-eclipse." This map from NASA shows that the transit will be visible from most of North America in the hours leading up to sunset (although Alaskans will be out of luck this time around).

The same eclipse safety rules apply to the transit: Don't gaze directly at the sun with your naked eye. Use the proper solar filters on your telescope, binoculars or camera. Feel free to make a pinhole projector, although Venus' tiny speck will be much harder to track than the effects of a solar eclipse.

Looking even farther ahead, there's a total solar eclipse on tap for Nov. 13, with the track of totality running across the northern tip of Australia and a wide expanse of the Pacific. That's the year's big prize for eclipse-chasers, but time is running out to make arrangements for a trip to Cairns or a Pacific cruise.

"A year or two is the rule for getting to a total solar eclipse," Doherty said. "But there's always this tradeoff between time ahead and money spent. If you want to go the less expensive way, plan early. If you're willing to pay a little bit more, go late."

The good news is that Americans have plenty of time to plan for a convenient total solar eclipse on Aug. 21, 2017. On that day, the path of totality will stretch diagonally across the United States, from Oregon to North Carolina. 

"That eclipse, you're just going to be able to drive to," Doherty said. "So if you miss this one, start planning now for 2017."

Tune us in online
To hear more tales of eclipses past, present and future, join us tonight for "Virtually Speaking Science," an hourlong talk show that plays out on BlogTalkRadio and in the Second Life virtual world. Doherty (a.k.a. Patio Plasma) and I will be at the StellaNova Small Auditorium, courtesy of the Meta Institute for Computational Astrophysics, starting at 9 p.m. ET (6 p.m. PT/SLT).

If you miss the live event, don't worry: It'll be archived by "Virtually Speaking" on BlogTalkRadio as well as iTunes.

On Friday, head on over to the Cosmic Log Facebook page for our weekly "Where in the Cosmos" picture puzzle. If you're the first to solve the riddle, you'll be eligible to receive a pair of sun-viewing safety glasses for this month's eclipse and next month's transit. In the meantime, check out these podcasts from previous episodes of "Virtually Speaking Science," plus links to eclipse-related resources:

Corrections for 10:25 p.m. ET: A couple of the Web links went to information about the November total solar eclipse when they should have referred to the May annular solar eclipse, but that's been fixed. I've also fixed the reference to the eclipse's timing in Albuquerque. From that location, the annular phase will last a little more than four minutes, from 7:33 to 7:38 p.m. MT, followed by sunset a little after 8 p.m. I originally (and erroneously) wrote that the "Ring of Fire" would occur four minutes before sunset.  

Alan Boyle is msnbc.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter or adding Cosmic Log's Google+ page to your circle. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for other worlds.