The exceptional duration is a result of the moon being near perigee, with the diameter of the moon 8% larger than the sun (magnitude 1.080). This is second in the series of three eclipses in a month. There was a lunar eclipse on July 7 and now a solar eclipse on July 22 and then a lunar eclipse on August 6.
This solar eclipse will last for up to 6 minutes and 39 seconds, in the maximum visibility area.
For more information, check out the Wikipedia page, Solar Eclipse of July 22, 2009.