The 190 - 420 metre wide asteroid 2008 QB will make a close pass (35.3 lunar distances, 0.0906 AU), travelling at 30.38 km/second, to the Earth-Moon system on the 20th August, 2012 @ 20:55 UT ±00:01.
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The Lunar Distance (LD), the distance between Earth and the Moon, equals 384,401 km, (or 0.00256 AU).