And to answer your question:
Thats what BBC LN are saying so far... But how is it heard in harrogate?
Once a craft is supersonic the shock-wave 'Boom' it creates is constant, a boom isn't just breaking the barrier, its the sound barrier being torn as the plane flies along. So as long as the aircraft was supersonic as it past you, you'll get the boom no matter where you are on its journey. I believe you got two as there were two fighters.
Concorde was only allowed to go supersonic over sea, if you were on a ship (or in a rubber dinghy) under its flight path in the middle of the ocean you would have heard a boom even if it was an hour in to its supersonic flight.
This is why commercial supersonic flight really fell on its arse and they only made a handful of supersonic airliners, no one wants that kind of inconvenience over their country. If you think that flying higher would solve things, sonic booms were audible on the ground from test craft flying as high as 70,000ft and Concorde flew between 50 and 60,000. Thats 11 miles up. Usual passenger planes fly up to 40,000, 45,000 max.
Altitude also complicates matters as in the high atmosphere the speed of sound is SLOWER than at sea level due to reduced temperature and pressure. Mach 1 is 761 mph at sea level and 20°C, but can be much lower at higher altitudes, for instance Feilix Bumgartner (spelled that wrong i'm sure) who dove from space had a local Mach 1 (speed of sound, essentially) of 447 mph. Thats still fast but it isn't 762 mph, (but he fell faster than that, too).
Hope I've helped explain some stuff, I work in a call centre by the way so you can discount the above as being the rantings of a madman.
