Science meets art: the sun gets a soundtrack

The sun gets a soundtrack (Image:NASA)

We've all seen mesmerizing footage of the sun's fiery surface as it bubbles and seethes at 6.5 million degrees, but now we can hear it! Researchers from University of Michigan and a composer from Alumnus School of Music have interpreted the sun's solar wind into music by a process called sonification. This has allowed them to understand events happening the sun in a whole new way.

Solar wind is the sun's atmosphere; a stream of charged particles emanating from the sun and expanding rapidly past us and beyond the solar system. Additionally short-lived events known as "coronal mass ejections" (CME) or solar flares make up what could be termed "space weather" that can have big impacts on Earth.

Particularly energetic solar flares have the capacity to short-circuit satellites, damaging them or parts of them irreparably. Flares have also been known to cause power outages on Earth and doomsayers will be familiar with the risk of a particularly large solar flare knocking out all our satellites and power simultaneously. It is therefore important for us to understand what's coming and when so we can take precautions. Our instruments on Earth continually measure the sun's temperature and density, and how fast solar flares are going and which direction they're coming from.

Thomas Zurbuchen, associate dean in engineering and an atmospheric science professor, thought perhaps scientists were missing information from the solar wind speed and particle density data by interpreting them visually in graph-form, and sought to further our understanding of the solar cycle through an interpretive process known as sonification. Together with Jason Gilbert, a research fellow in the Department of Atmospheric, Oceanic and Space Sciences, and Robert Alexander, composer at Alumnus School of Music they began the process of sonification which takes each form of data from the solar wind and interprets it musically.

The process was performed on solar wind data captured by the NASA’s Advanced Composition Explorer satellite in 2003. Robert Alexander started by analyzing the features of terrestrial wind, and generated the sweeping wind sound from both solar wind density and velocity. The velocity measured controls the cut-off frequency of a band-pass filter placed over pink-noise which creates a whooshing sound, while the density dictated the volume of the wind sound; a higher density leading to a louder wind. During a solar flare this is further amplified and processed with a form of distortion known as overdrive which causes the wind to swell and ebb in a more pronounced manner.

Changes in the carbon state distribution were matched to six distinct vocal layers, while the value average charge state of carbon is represented by a further set of vocals, provided by Alexander's sister, singing in a higher register. The ratio of solar wind density to oxygen (He/O) is represented by a chord composed of an extremely high frequency set of triangle waveforms which could be described as a "glistening". During a CME the reverb suddenly swells to much higher volume before receding gently back to a baseline which creates a feeling of sudden expanse. A tribal beat was overlaid to represent the rotation of the sun and the playback speed of the data is scaled so that the rotation lines up precisely with the tempo of the music set at 150 beats per minute (bpm). This means a full Sidereal Carrington rotation (25.38 days) takes place every eight measures.

The researchers found that they could now hear when the temperature of the sun is elevated, or when density increases but in fact did not detect any new information as a result of the sonification. However Zurbechen remains proud of the beautiful, ethereal music produced by the project. “To me, this project exemplifies what University of Michigan is about: creativity reaching seamlessly across many fields to create something new,” he said.

“Every piece of scientific data tells a story. I'm expressing this story through music,” said Alexander.

“I am excited for sonification’s potential in research, but I think more work will need to be done to realize that potential,” summed up Jim Raines, research computer specialist with the Department of Atmospheric, Oceanic and Space Sciences.

"The Dynamic Sun" DVD by NASA/Sun-Earth Connection Living with a Star Program. Video clips have been arranged such that auditory events often correspond visually to solar flares or CME events.

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