As you read this, an asteroid has already whizzed past Earth, coming close at a distance a little more than the moon’s. From the Register’s report:
The asteroid, dubbed 2004 XP14, had been flagged as a potentially hazardous object when it was discovered in 2004. Australian astronomers have been tracking its approach to make sure the calculations showing it would miss us were correct. Their work shows that the object will zip past Earth at 05:25 tomorrow morning, barely further away than the moon.