The 16 - 36 metre wide asteroid 2014 SL1 will make a close pass (27.8 lunar distances, 0.0714 AU), travelling at 5.28 km/second, to the Earth-Moon system on the 21st September 2014 @ 10:23 UT ±00:09.
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The Lunar Distance (LD), the distance between Earth and the Moon, equals 384,401 km, (or 0.00256 AU).