Ellie Arroway is a young radio astronomer played by Jodie Foster in the 1997 film Contact. Ellie is on her mission to detect extraterrestrial life, and in a famous scene from the Very Big Array, she sits on the edge of the observatory listening to the radio sounds of the sky with antennae antennae in the background.

It’s a great cinematic moment that underscores Ellie’s solitary quest for truth, and it’s become so iconic that many VLA visitors get “that shot” with headphones while standing in front of a radio dish. But as beautifully poetic as this scene is, it’s Hollywood magic, not science. Radio signals from Ellie’s headphones and computer interfere with the observatory’s sensitive equipment, so radio astronomers don’t listen to the sky.

The idea that radio astronomers listen to celestial bodies is probably the biggest misconception in radio astronomy. And it’s understandable to some extent. People listen to the radio all the time, so radio astronomers should do the same. However, the sounds we hear on the radio are not the sounds of the radio itself. They are converted from electrical signals. Sound waves need a medium to travel, such as air, and since space is essentially a vacuum, sound cannot travel through it. If astronomers listened to the sky, they would hear nothing but silence.

Radio is a form of light. It is like visible light, but with a much longer wavelength. Visible light has wavelengths at the atomic scale, while radio light has wavelengths from the thickness of a pencil to the length of a tire.

Because radio wavelengths are on a human scale, radio astronomy technology is often very different from optical astronomy technology. There are so many similarities. Both optical and radio astronomy use reflective surfaces to focus light on a detector or receiver, which converts the light into a digital signal. Astronomers can then use this digital signal to create astronomical images. But since radio wavelengths are much longer than visible wavelengths, we must achieve this feat in several ways.

One of the key factors is the size of the reflector. In general, the larger your reflector or mirror, the more light you can focus on and the sharper and brighter your image will be. This is why the best optical telescopes have mirrors several meters in diameter. But the size of your reflector should match the size of your wavelength. Because radio waves are thousands of times longer than visible waves, the mirror of a radio telescope must be larger than Manhattan. It’s not something we can create, instead we create arrays of smaller plates. Each aerial antenna acts as part of a larger mirror. Astronomers can then combine data from a series of small dishes to simulate a city-wide dish.

Another factor is that radio light is usually much dimmer than visible light, and there are many things that make radio light. This means that radio telescopes must be protected from everyday objects such as cell phones and computer equipment that emit radio light. Antenna receivers must also be very cold. Objects at room temperature emit a lot of weak radio light, which can affect the accuracy of observation data, so the receivers and other electronics of the radio telescope must be supercooled to convert the radio light into a digital signal.

Of course, once astronomers have their data, they can always translate it into audio. This is most famously done with pulsars, where bursts of electrical energy from a neutron star are converted into audible bursts. Astronomers have also transformed phenomena such as Jupiter’s stormy aurora or the howl of a distant nebula. These sounds can give us an emotional connection to the cosmos, but like the scene in Contact, they are just a poetic interpretation of the radio light we receive.