Night Physics

Tonight I was experimenting with photographing the moon (bottom left - how do you capture this properly?), and the result was this happy accident that would delight a school science teacher.

The trail from centre to top right is an airplane's vapour trail. But planes at night have a flashing light on them, captured here as three dots at the leading edge of the trail. So in the exposure time of this photo, the light flashed three times, travelling the distance shown between the three dots. This reminds me of the ticker-tape experiments we used to do in O-level Physics. You could probably calculate various things from this (speed? acceleration?), but I'm not a good enough physicist to work it out.

Any ideas? No calculators allowed.