How to watch as NASA sends a spacecraft to deliberately crash into a 525-foot-wide asteroid at 15,000 mph

NASA scientists are gearing up for the world's first mission testing planetary defense — and they want you to watch this evening.

The space agency's Double Asteroid Redirection Test (DART) will test technology to defend Earth against future asteroids and comets by deliberately crashing into an asteroid — which poses no threat to Earth — at some 15,000 mph. The target, a larger asteroid's moonlet named Dimorphos, measures about 525 feet wide.