Astro Bob: Hear the drone of a nebula, the tinkle of a star

A new technique called sonification turns astronomical images into paintings of sound.

Sonification M16.jpg
Using sonification, astronomers have converted the data in a picture, like this one of the "Pillars of Creation" in the Eagle Nebula, into a soundscape. Contributed / NASA/STScI; Sonification: NASA/CXC/SAO/K.Arcand, SYSTEM Sounds (M. Russo, A. Santaguida)

Julie Andrews had it right. When she sang "Do-Re-Mi" in the "Sound of Music," she used simple syllables to teach a musical scale, then mixed up their order to create new songs and melodies. The process of assigning notes to syllables is called solmization and originated in ancient India.

In a similar manner, astronomers now use sonification to turn astronomical images from the Chandra X-ray observatory and other telescopes into sound. First, let's be clear about outer space. It's basically a vacuum, so space ships, spinning planets and even exploding stars don't make a sound. Not even a whisper. To reach our ears their rumblings require a medium such as air, water or solids. Thinking about that much silence makes me love this planet that much more.


But there's nothing stopping us from assigning sounds to things in space to create a sonic picture of a nebula, star cluster or galaxy. In the videos included here, stars and other compact sources are converted to individual notes, while broader drones depict clouds of nebulosity. Each picture is further divided by pitch, with higher notes nearer the top of the image and lower ones below. And just as you'd expect, the brighter the star or nebula, the louder the volume. As the cursor moves across the image, sounds represent the position and brightness of the sources. Listening to a sonification is rather like reading a book written in tones instead of words.

When I first heard of sonification, I thought of my old friend Bryan from college. He and I traveled through Europe back in the day, visiting shops, historical sights and museums. One day, somewhere in Italy, we discovered an out-of-the-way exhibit of paintings by an Italian artist whose name escapes me. Since Bryan was blind, I did my best to explain the scenes and people depicted in the art, along with the technique the painter used to give them depth. I'm glad it wasn't a gallery of astronomical images or I would have been at a complete loss.

Sonification provides a way not only for people who are blind to gain a better perception of celestial objects but adds a delicious layer of aural information to an otherwise silent scene. Astronomers frequently study the sky well beyond the visual spectrum, employing telescopes that can see into the infrared, ultraviolet, X-ray and radio. Each provides a unique perspective on the subject. Adding sound to a photo feels like that by going beyond the visual sense.


In the topmost soundscape you're looking toward the center of the Milky Way Galaxy about 26,000 light-years from Earth. Images from three telescope were combined into a composite. The Hubble photo depicts bright clouds called nebulae where stars are being born. NASA's Spitzer Space Telescope's infrared eye shows glowing clouds of dust, while Chandra's X-ray vision spotlights gas heated to millions of degrees from supernovae explosions, along with of hot, ionized gas from the supermassive black hole in the galaxy's heart.

Together, the three views create a mini-symphony of cosmic music. There are also sonified versions of Hubble's famous "Pillars of Creation" inside the Eagle Nebula, the expanding remains of the supernova Cassiopeia A (Cas A) and many others.


In Cas A the sounds are mapped to the distribution of four key elements found within the stellar debris: silicon (red), sulfur (yellow), calcium (green), and iron (purple). Intensity of the light emitted by those elements controls the volume. At the center of the puff lies a city-sized, super-dense neutron star, representing the original star's leftover core.

As you watch Friday morning's near-total lunar eclipse , try listening closely and imagining what it might sound like.

"Astro" Bob King is a freelance writer for the Duluth News Tribune. Read more of his work at .

"Astro" Bob King is a freelance writer and retired photographer for the Duluth News Tribune. You can reach him at
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