While I was waiting with Jesse and Laura for the train from Radburn back into the city yesterday, I did a little back-of-the-envelope calculation to try to figure out how fast a train would have be traveling in order to get from out of sight over the horizon to being at the station before you could see it approaching. Here's the rough calculation:
The distance to the horizon
is about 2 miles (I'm decreasing it a little due to city smog). And we blink for about 300 milliseconds
. So for a train to come out of nowhere, it'd have to travel 2 miles in 300 milliseconds. Or 1 mile per 150 milliseconds. Do the math
and that's 24,000 miles per hour. Roughly Mach
31, but only about one and a half times faster than the space shuttle orbits the earth.