Shoot me, baby!

Among the topics that arose after Saturday's run was the question of whether long-range snipers have to correct their aim for the effects of the earth's rotation. Fortunately The Online Scum didn't have to look far for an answer: the redoubtable Cecil Adams ("The world's most intelligent human") has already tackled the subject here. The short answer: yes, but not much.

The cause is our old friend the Coriolis Effect, which you probably already know from the question of whether water drains clockwise or counter-clockwise depending on whether you're north or south of the equator. (Cecil provides a definitive answer to that one too, here.) Put simply, bullets travel in a straight line, but objects on the earth's surface don't. Cecil's example, at a latitude somewhat north of us, shows that at a range of 1000 yards, a bullet will deflect about three inches to the right. More important is the vertical deflection: if aiming due west, for example, it will also appear to deflect about six inches upwards (due to the target's drop by that amount as the earth rotates).

And yes, despite claims to the contrary, most bullets travel at supersonic speeds. Sniper rounds apparently have a typical muzzle velocity of around 900 m/s, almost three times the speed of sound (350 m/s). The idea is that the bullet reaches the target before it has slowed to transonic speed (mach 0.8-1.2), where strange things can happen to its trajectory. One effect of this, of course, is that the target only hears the shot a few seconds after being hit.