NASA scientists say asteroid 2004 BL86 will come closest Monday. That will be the nearest the asteroid gets for another 200 years. And it will be the closest known encounter by such a giant space rock until another mega-asteroid flies by in 2027.
It was discovered in 2004 and is estimated to be about one-third of a mile in size, or between 1,600 and 1,800 feet.
Amateur astronomers across North America should be able to see it with telescopes and binoculars.