This is College Physics Answers with Shaun Dychko. We want to know how much time between an asteroid colliding with the moon would elapse before someone on earth would see that collision. And, we can say that the distance the light travels from the moon to the earth equals the speed of light in a vacuum multiplied by time. And so, we'll divide both sides by <i>C</i> to solve for <i>T</i>. So, <i>T</i> is distance over speed. So, that's 3.84 times ten to the five kilometers between the earth and the moon but then we multiply it by ten to the three due to the prefix kilo. So, this is really times ten to the eight. And then, we're dividing by the speed of light three times ten to the eight meters per second, giving a time of 1.28 seconds. So, if an asteroid hit the moon, we would see that collision, 1.28 seconds, after if occurred.