A small noise begins as a low rumble, barely noticeable in the distant sky. It’s not much louder than an old car. But soon the noise becomes a ferocious roar, tearing through the heavens in explosive crescendos louder than any orchestra. The very air shakes and vibrates as the now tremendous clamor overshadows almost every other sound. What’s happening? Is this the apocalypse? No, it is only a fighter jet preforming maneuvers.

Any Madison College student taking classes on the Truax campus has likely heard the booming symphony of the jets as they fly overhead. With the airport in close proximity to the school, it is almost impossible not to hear them. But what are these aircraft and why are they so loud?

The noise from a jet comes from two sources – the engine itself and the reaction the exhaust has with the surrounding air. A jet engine works by taking in air through the intake and compressing it as much as 12 times its original pressure. From there, fuel is injected into the compressed air and sent to a combustion chamber where the air-gas is ignited. Once ignited, the highly pressurized air-gas mixture is pushed through a turbine and out a nozzle at the rear of the engine, giving the aircraft its thrust. The more energy needed to ignite the air-gas mixture and expel it from the engine, the louder the engine will be. In layman’s terms, the louder the jet the less efficient it is.

The hot exhaust makes a sound of it’s own. After it leaves the turbine and exits the nozzle, the exhaust is traveling at a much faster rate than the air flowing around it. Vapor in the exhaust sometimes condenses as clouds, forming the iconic white tail most aircraft leave behind at high altitudes known as “contrails.” The incredible resistance of the hot exhaust and the cooler air is what gives most jet engines their thunderous and crackling roar.

But just how noisy is one of these aircrafts? A decibel (dB) is a unit of measurement that uses ratios to measure sound, with 60dB being the noise level of an average conversation. Imagine standing close to one of the speakers at the loudest rock concert possible, measuring around 115dB. Even without hearing protection and standing only a few feet away, the noise from the speakers would do little to mask the sound of a jet passing 100 feet overhead rated at 140dB. This is only 40dB away from the point where hearing tissue begins to die, and 54dB from the loudest sound possible.

But not to worry, it would take repeated exposure to such high decibels at close ranges for significant hearing loss to occur. Jets generally fly at high enough altitudes so that the sound emitted from them has dissipated well before it can do damage to anyone at ground level.

The next time the sky echoes with massive vibrations and tremendous sound, don’t look for the end of the world, just look for a jet.