Asteroids nearest the Earth: it arrived without calling!
All jokes aside, the huge asteroid 2012 LZ1 (diameter of about half a kilometer) passed to 5.3 million kilometers from our planet. Only a few decades ago, most scientists thought it was ridiculous to think that a so big asteroid could hit Earth without being observed by telescopes with a good advance.
But today scientists are concerned not only that an event similar to what has caused the extinction of the dinosaurs could occur, but they have set up programs to catalog all the heavenly bodies that could hit the Earth.
2012 LZ1, evidently, has escapet to the detection from astronomical devices: it was not a dangerous transit (it passed on our head Thursday), although the discovery was only a few days before, but it is a bit disturbing when one considers the immense size of the asteroid.

In the video: the passage of the asteroid, observed from the Canary Islands Slooh Observatory
Translation in english from this italian post