What is a sonic boom?

Millions of Britons heard a “massive explosion” on Tuesday afternoon. But it was just a sonic boom, created as RAF Typhoons broke the sound barrier to escort a private jet arriving from Germany.

Javelin Sam from Essex caught the boom on his doorbell camera:

The boom was reported to be heard across London and Cambridge.

‘Quick Reaction Alert’ procedures allow for RAF aircrafts and crews to travel at supersonic speeds, to allow for operational effectiveness when necessary. The ‘bomb’ sound was fortunately worth it – the planes all landed safely at Stansted.

Ok, but what actually makes a sonic boom happen?

We’re good, but we’re not that good. NASA to the rescue:

A sonic boom is a thunder-like noise a person on the ground hears when an aircraft or other type of aerospace vehicle flies overhead faster than the speed of sound, or ‘supersonic.’

“Air reacts like fluid to supersonic objects. As those objects travel through the air, molecules are pushed aside with great force and this forms a shock wave, much like a boat creates a wake in water. The bigger and heavier the aircraft, the more air it displaces.  

The sharp release of pressure, after the buildup by the shock wave, is heard as the sonic boom.

The change in air pressure associated with a sonic boom is only a few pounds per square foot – about the same pressure change experienced riding an elevator down two or three floors. 

It is the rate of change, the sudden changing of the pressure, which makes the sonic boom audible.”