【英语时差8,16】陨星（下）（在线收听）

But there’s another reason. Remember that the earth doesn’t sit still in space: it’s orbiting the sun at 18.5 miles per second. Meteors that are coming towards us go faster across the sky because of earth’s forward velocity. It’s like two cars passing in opposite directions. In general, the fastest meteors to enter our atmosphere move at about 26 miles-per-second. Add earth’s forward velocity to that and it goes up to almost forty-five miles a second. Zoom! These kinds burn up and are gone in less than one second. Meteors that come from the other direction, however, are essentially chasing the earth through space. Their speed is decreased by the same amount as our forward velocity. That’s like two cars passing while travelling in the same direction. The speeds cancel out and the passing car seems to be going much slowly.