Today the moon will take a bite out of the sun.
In what is known as an annular eclipse, the moon will pass directly between Earth and the sun, casting the moon's shadow our way.
An annular eclipse is only a partial darkening of the sun because it occurs when the moon is at or near the furthest point of its elliptical orbit. This distance (about 252,000 miles away from Earth) makes the moon appear smaller than the sun so the sun's rays are not completely cloaked.
Annular (meaning "forming a ring") refers to the ring of the sun's fire that is left exposed as the moon's disk passes in front.
Shows Vary by Location
Costa Rica and Nicaragua are in the direct line of the annular eclipse and people there will experience the most dramatically darkened skies, says Fred Espanak of NASA's Goddard Space Flight Center. As viewed from these countries, the moon will cover about 96 percent of the sun's glare.
See a map of viewing times by location here.
In the United States, the extent of the eclipse will depend on location — with the most spectacular event appearing over Hawaii. Only a sliver of sun will remain there as the moon blocks 79 percent of its surface.
In the Southeastern U.S., Espanak says, the magnitude of the eclipse will range from about 30 percent in Texas to 60 percent over southern Florida. In the Midwest and Southwest about 20 percent of the sun will be eclipsed and in the northwest and southern Alaska, the moon will block about 10 percent of the sun.
Those in the Northeast, and particularly New England will not see much effect since the eclipse is due to begin just before, during or after sunset. In Hartford, Conn., for example, the eclipse begins after sunset and in New York City the moon's shadow is due to appear at 4:13 p.m. ET — only 16 minutes before sundown.
Still, Mitzi Adams, an astronomer at Marshall Space Flight Center, expects today's annular eclipse could provide an unusually beautiful show from some locations. The eclipse is scheduled to peak just around sunset where she's based in Huntsville, Ala.
"I suspect the combination of the sunset and the eclipse could be very pretty," she said.
Annular eclipses can also reveal a phenomenon known as "Baily's Beads." These are a string of glimmering spots produced as the backlight of the sun illuminates the moon's bumpy canyons and craters.
Science in the Dark
But take heed, looking directly at the sun — even during an eclipse — can cause severe eye damage. Devices like exposed black and white film negatives, welder's glass No. 14, solar eclipse glasses made from aluminized mylar and pinhole cameras are among a few ways to watch the eclipse safely.
Annular eclipses aren't just pretty, they also provide valuable glimpses of the sun's outer layers. Normally the light of the sun is so bright it effectively obscures anything in its nearby fields, including the sun's outer atmosphere known as the corona. But as the moon turns out the main light of the sun, scientists can watch for dust and silicon circling amid these outer fields.
"Think of a lava lamp," explains Adams. "A bubble of oil will start at [the] bottom and diffuse upward. That's kind of like what we're observing during an eclipse, but it's not solid — we're observing the effects of the light on the magnetic fields of the sun."
There are satellite instruments in space (known as coronagraphs) that can offer similar glimpses by blocking their local view of the sun and relaying images of the sun's outer fields to Earth.
But nothing blocks the sun's blinding rays as effectively as the moon and exposes such a 'big picture' view of activity at the sun's edges.
As Adams says, "It's like seeing the trees instead of the forest."