Listening to Meteors
Did you know that you can “hear” meteors? meteor trails – those columns of ionized atoms and molecules that we see as bright streaks – reflect radio waves that can be broadcast as audible pings.
These “specular” reflections offer alternative observing methods and valuable scientific data. In fact, radio equipment is capable of detecting even smaller particles than visual observations and it can be employed during daylight hours or on cloudy nights.
There are two main types of meteor trails, each of which is determined by the density of free electrons, and each of which broadcasts distinct signals. Underdense trails typically represent fainter meteors and can be heard as sharp, quick pings, while overdense trails are caused by brighter meteors and have a slower signal rise with a sustained peak.
Other radiometeor events include oscillating, transition “bongs”, and meteor head echo “whistles”. Each has a different sound, and all are distinct from non-meteor signals, such as passing aircraft, which typically result in longer-duration, steady-pitch signals.
There are also two primary types of radio observing methods. With the back-scatter (radar) method, the transmitter and receiver are located together, so that the radio signals are reflected back to where they started. With forward-scatter, the signal is reflected forward to the receiver, which is located many kilometers from the transmitter.
Listening to meteors can be as simple as tuning your digital FM radio to a distant known frequency that you cannot hear (meteors are heard as brief bursts of speech or music.) Serious observers can set up a relatively inexpensive personal radio observatory, which can also be used in other radio astronomy, such as tracking solar flares and detecting Jovian radio storms.