BANNERS: Near Miss Day! | March 23

On March 23, 1989, a 300-metre asteroid called 4581 Asclepius flew past Earth by about 500,000 miles (804,000 kms). That was a 'near miss' in interstellar terms.

"On the cosmic scale of things, that was a close call," said Dr. Henry Holt, an amateur astronomer from Flagstaff, Ariz., who discovered the asteroid while working on a NASA project.
Bevan French, a scientist with NASA's solar system exploration division, said if the asteroid had collided with Earth the impact would have been equivalent to the explosion of 20,000 hydrogen bombs and would have created a crater at least 5 miles across--or "enough to destroy a good-sized city."
If it had hit an ocean, it would have caused tidal waves that would have swept over coastal regions, French said. - latimes