Starting at dawn in eastern Brazil, then sweeping across northern Africa and central Asia before ending at sunset in Mongolia, the moon will block the light of the sun for several minutes today in a narrow band of territories. Observers in Africa, Europe and Asia who are outside that path will be treated to a partial eclipse.
Such a total eclipse is relatively rare--the next one for observers in the U.S. will not happen until August 21, 2017--because the moon must cross our planet's orbital plane exactly when it, Earth and the sun are aligned, and its nighttime side faces us. This eclipse will offer astronomers a chance to study the corona--a super-heated, spectral cloud of emissions surrounding the sun--and NASA scientists have set up camps in Africa to attempt to observe the direction and speed of matter in the solar atmosphere as it is shaped by the sun's magnetic fields.
This eclipse is even more special because whereas in most total eclipses totality lasts for less than two minutes, this time the moon will block the sun's light for more than four minutes in the center of the eclipse path. During those four minutes, the affected swath of land will be completely dark and stars will be visible in the sky, along with the normally indiscernable solar corona.
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NASA has planned a series of webcasts, podcasts and live television coverage of the eclipse from Turkey beginning at 5 A.M. Eastern Standard Time. More information can be found here.