http://www.spaceweather.com/
A relatively large asteroid, just discovered on August 28th, will fly past the Earth-Moon system on Sept 14th only 2.8 million km (7.4 lunar distances) away. 2012 QG42 is about as wide as three football fields and comes to us from just beyond the orbit of Mars. Astronomers who are now monitoring the space rock say it shines about as brightly as a 15th magnitude star.
What's scary to me is that it was just discovered. So how many more are lurking out there this close and this big?