Tonight, if all goes well, NASA’s Double Asteroid Redirection Test — or DART — mission will slam into a tiny asteroid moon at nearly 24,000 kilometers per hour, blasting out a cloud of debris, creating a flash of light visible across the solar system, and changing the velocity of the asteroid by less than a millimeter per second… which is tiny, but significant. Impact is planned for 23:14 UTC tonight, which is 7:14 p.m. ET. The flash won’t be visible by eye, but may be observable in small telescopes — see my caveats below. It will be observed by professional astronomers across the planet and by observatories above and beyond it, too.  The point? To see if hitting an asteroid at high speed is possible, to test the mechanics and engineering of it, and to hope that, if one day we see a space rock with our number on it, this method can be employed to prevent Earth from having a Very Bad Day .…