Okay "all the way across the sky" really means they got 5.2 million kilometers away at their closest. But still, double asteroids!!! Look at 'em. The International Asteroid Warning Network (IAWN) and the European Southern Observatory's Very Large Telescope (VLT, actual name) spotted Asteroid 1999 KW4 in late May. Here's a NASA .gif of the asteroid, which has two parts (making it a "binary" asteroid). Alpha is the bigger one, the "primary" body, and Beta, the smaller one, is the secondary body but is also sometimes adorably called a "moonlet."

(NASA/JPL)

Although 1999 KW4 isn't a threat, since the closest it came to Earth is 15 times further away than the Moon is, it's being treated as a kind of rehearsal for observing other potentially dangerous objects. 1999 KW4 is also reminiscent of Didymos, another binary asteroid (its moonlet is called Didymoon). NASA will be attempting to deflect Didymoon in 2022, to see if changing an asteroid's course is possible. I'm already working on my screenplay.