After two RAF Typhoons were scrambled to intercept a civilian aircraft last week, a sonic boom was heard across London, Cambridgeshire and Essex.
But what is a sonic boom?
Firstly, when travelling at subsonic speed – anything below 767mph – pressure waves move away from an aircraft in all directions.
At the speed of sound, 767mph, the waves compress to form a shockwave.
But, when the speed of an aircraft exceeds the speed of sound, as NASA explains on its website, the air reacts like a fluid.
As a supersonic object moves through the air, molecules are pushed out of the way with huge force, creating a shockwave – like a boat creating a wake in the water.
These molecules, or waves, then merge into one single shockwave cone of pressurised, built-up air molecules which move in all directions and extend all the way to the ground.
And it is the release of pressure, after the build-up of a shockwave, when the sound of the sonic boom is heard.
According to the US Air Force, an aircraft will continuously create shock waves, producing sonic booms along its flight path.
They also state that "from the perspective of the aircraft, the boom appears to be swept backwards as it travels away from the aircraft".
If an aircraft was to sharply change direction or pull up, the sonic boom would then strike the ground in front of the aircraft.
There are multiple factors which may influence a sonic boom, including the weight, size and shape of an aircraft.
The larger an aircraft is, the more air it must displace and the more lift it must create to sustain flight so, the larger the aircraft, the larger the boom.
Additionally, altitude, attitude, flight path and weather or atmospheric conditions can also affect the size of a sonic boom.
Cover image: RAF Typhoon FGR4 from RAF Coningsby (Picture: MOD).