Tonight the moon takes a big bite out of the midnight sun.
A partial solar eclipse visible from far-northern parts of the Europe and Asia—including areas where the sun doesn't set during this time of year—will turn the sun into a glowing "smile" hugging the horizon, astronomers say.
"It is always exciting when the moon eclipses the sun, but the eclipse of June 1 will be seen by few people, because it will be visible only from Arctic and other extreme northern regions," said eclipse expert Jay Pasachoff of Williams College in Massachusetts.
Solar eclipses occur when Earth, the moon, and the sun are aligned so that—as seen from Earth—the moon appears to cover all or part of the sun's disk.
Partial solar eclipses, such as tonight's, which is the second of 2011—happen when Earth crosses only through the faint outer part of the moon's shadow, known as the penumbra. (See pictures of January's partial solar eclipse.)
By contrast, during a total eclipse the sun is completely blotted out by the moon as its dark, central shadow, called the umbra, falls in a very narrow strip along Earth's surface.
(See "ring of fire" solar eclipse pictures.)
Anatomy of an Eclipse
The first hint of the moon's silhouette taking a bite out of the sun's disk will be seen from northern China and northern Japan between 4 and 5 a.m., local time, on Thursday. Shortly thereafter, about 60 percent of the sun will go dark over Siberia, Russia.
Moving east to west, the solar eclipse's pathway will cross the date line, so far-northern European observers—who should wear specially filtered protective eyeglasses or watch through a telescope—will effectively see the eclipse around 11:30 p.m. Wednesday.
In European eclipse spots, nearly 43 percent of the sun will appear to be blocked.
The partial solar eclipse will then race across Iceland—which will see 46 percent of the sun disappear—en route to North America.
In Canada, Atlantic Provinces cities, such as St. John's (map) in Newfoundland, will see only 12 percent of the sun vanish, at 8:09 p.m. Canada's northernmost reaches will see between 25 to 35 percent of the sun blocked.
In the U.S., Alaska will catch the tail end of the sky show at midday (1:09 p.m.), though with only one percent of the sun obscured.
Next Solar Eclipse Even More Remote
The next solar eclipse, on July 1, will be even more obscure than tonight's—visible from only a small patch of ocean off Antarctica, said Pasachoff, whose work has been funded by the National Geographic Society's Committee for Research and Exploration. (The Society owns National Geographic News.)
"No airplane flights seem to be passing through that region at the proper time," he said. "So it is probable that no human will see it."
All in all, 2011 isn't exactly a solar eclipse buff's dream, with only four partial and no total eclipses. "That hasn't happened since 1982, Pasachoff said. On the bright side, such a paltry lineup won't happen again until 2029.