An asteroid up to 1600ft in diameter is set to fly by Earth in the early hours of March 7. Named “2017 VR12”, NASA has called the object “potentially hazardous.” But don’t worry—the space rock shouldn’t get closer than 900,000 miles from Earth. That’s far enough to stay safe, and maybe even close enough to watch on a home telescope. Larger than the Empire State Building? It is difficult to work out an asteroid’s size at great distance, but we can estimate. “The asteroid is a mere point of light in our telescopes: we cannot resolve its size that way,” Paul...