What causes a sonic boom? Everything you need to know after this morning's incident in Derbyshire
This morning a sonic boom could be heard across Derbyshire.
It was caused by two RAF jets travelling at high speed to an emergency incident.
At about 9.50am, residents across the county, particularly in the Ilkeston and Derby areas, reported hearing a 'loud bang' which caused homes to shake and set off car alarms.
The noise was soon confirmed by Derbyshire police to be two RAF Typhoons passing over the county as they headed to a security alert on an Air India Boeing 777 plane travelling from Mumbai to Newark.
Thankfully, this was not the case.
But the RAF jets did escort the plane to London Stansted Airport.
An RAF spokesman said: "The RAF can confirm QRA Typhoons were launched this morning from RAF Coningsby to intercept a civilian ac [aircraft].
"The ac was escorted to Stansted. The Typhoons transited at supersonic speed for operational reasons; any inconvenience caused to local residents is regretted."
A spokesperson for Essex Police said: "An aircraft was diverted to Stansted Airport at around 9.50am today following reports of a security alert. The plane is currently at the airport and officers are making enquiries."
And a spokesperson for London Stansted Airport said: "An Air India Boeing 777 diverted into London Stanstead Airport at approximately 10.15am and landed safely with Essex Police in attendance.
"It is parked on an isolated stand away from the normal airport operations.
"Our runway has now re-opened and is fully operational. We are very sorry for any delays and disruption caused by the incident, but our first priority is always the safety of passengers and staff."
But what exactly is a sonic boom?
A sonic boom is an incredibly loud sound that sounds similar to an explosion, which is what residents reported hearing this morning.
As we mentioned, the RAF Typhoons were travelling at very high speeds, around 770mph.
When an aircraft reaches this level of speed, the air in front of the plane builds up a pressure front because it has nowhere to escape.
The sonic boom then happens when the trapped air escapes.
The reason the sonic boom can be heard over such a large distance is because it moves with the plane.