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Ring of Fire: The science behind Sunday's annular eclipse

Doug O'Harra

Alaskans have a chance to catch a glimpse of a partial solar eclipse on Sunday afternoon. That’s when the moon will pass in front of the Sun and cast a shadow across the home planet’s surface on a trajectory that begins in Asia and crosses the ocean into North America.

“Something strange is about to happen to the shadows beneath your feet,” teases NASA’s eclipse story with gobs of links and graphics, “transforming sunbeams across the Pacific side of Earth into fat crescents and thin rings of light.”

The moon’s penumbral shadow will darken most of Alaska during the event. In Anchorage, the eclipse will commence at one second past 3:17 p.m. Alaska Daylight Time, reach its maximum coverage about 4:37 p.m. and end just before 5:54 p.m., according to NASA’s solar eclipse calculator.

Here’s an animation showing how that might look in various locales, including Anchorage. Though the forecast appeared favorable on Friday and Saturday for those viewing in Southcentral, with partly sunny skies predicted, those hopes diminished by the day of the eclipse.

"Clouds are forecast for much of the state today and it is unlikely that there will be enough breaks in them for those in Southcentral and Southeast Alaska to witness the eclipse," the National Weather Service reported. "By contrast, those of you in the Interior may have a chance. Generally clear to partly cloudy skies will give way to more clouds and showers by afternoon but there will be areas where the partly cloudy skies remain over the Interior."

Meanwhile, it was also cloudy in much of the Aleutians, where the chances of the most pronounced eclipse would be visible along the western portions of the island chain. See the forecast for your region, here.

The narrow path of the more intense annular eclipse -- where the moon appears directly in front of the Sun to block about 94 percent of its surface -- will cross the Pacific Ocean south of the Aleutian Chain. For observers in this zone, the sun might appear as a dazzling ring around the darker body, hence the name, “annular,” which came from a Latin word meaning “ring.”  

“While Anchorage and the rest of Alaska will see the eclipse with the moon off-center from the sun, the full ring effect of the annular phase will be visible from Taiwan to Lubbock, Texas in an arc across the North Pacific south of Alaska,” wrote Mike Dunham, in a particularly detailed eclipse advance posted by the Anchorage Daily News. “The maximum coverage of the sun -- hence the thinnest ring -- will be seen just south of uninhabited Amatignak Island in the Aleutians, about 125 miles southwest of Adak and the southernmost point in Alaska.”

NASA’s page for this eclipse has lots of other information, including a highly detailed chart. For the ultimate primer on eclipses, check out NASA’s main eclipse page, with its catalog for eclipse dates reaching 1,000 years into the future. Anchorage’s next partial will darken local skies on Oct 23, 2014.

Contact Doug O'Harra at doug(at)alaskadispatch.com