The near-Earth asteroid 2012 DA14 is about half the two-dimensional size of a football field, with a length of about 148 feet (45 meters).
Its approximate weight is 143,000 tons (130,000 metric tons) .The asteroid is expected to pass by Earth from a distance of about 17,200 miles (27,700 kilometers).
According to the January 29, 2013 USA Today article NASA: Asteroid to give Earth close shave, "NASA asteroid expert Don Yeomans, author of Near-Earth Objects: Finding Them Before They Find Us, compares the asteroid to the one that leveled hundreds of square miles of Siberian forest in the "Tunguska Event" in 1908."
And, "Only this time Earth won't be hit, the space agency says. Sky watchers might want to keep their eyes peeled that evening as the asteroid should be visible with a backyard telescope. The only problem will be tracking the space rock. It will sail twice the width of the moon across the sky for every minute that it is visible, making it tough to track."
Astronomers at the Observatorio Astronómico de Mallorca (OAM, in English The Astronomical Observatory of Mallorca), which is near La Sagra in Spain (just south of Costitx, Mallorca, Spain), discovered the asteroid on February 23, 2012.
The NASA video "ScienceCast: Record-Setting Asteroid Flyby" discusses this event on YouTube (http://www.youtube.com/watch?v=rtesZxRlqOE).
Its caption states, "Published on Jan 28, 2013: On Feb. 15th an asteroid about half the size of a football field will fly past Earth closer than many man-made satellites. Since regular sky surveys began in the 1990s, astronomers have never seen an object so big come so close to our planet."