What Does The Sun Sound Like?

What sound does the Sun make, and would it be musical if we could hear it?
This montage of 366 images shows our Sun through the eyes of ESA’s Proba-2 satellite, as seen each day in 2016. The satellite’s SWAP camera works at extreme ultraviolet wavelengths to capture the hot turbulent atmosphere of the Sun, known as the solar corona. Each image was created from 30 separate images centred on 01:00 GMT each day, which were processed to enhance the features extending from the solar disc. Throughout 2016 the Sun’s 11 year activity cycle continued towards its minimum, a period when the number of sunspots, active regions, solar flares and eruptions diminish. Nonetheless, the most active region of last year can be seen in the 17 July image. The bright region close to the centre of the Sun produced eight of the 20 most powerful flares witnessed last year. Other prominent features are coronal holes – darker regions indicating lower levels of emission. However, coronal holes can produce streams of fast solar wind that can trigger geomagnetic storms on Earth. One of the largest holes observed last year can be seen towards the north of the Sun on 24 November, and was present for several solar rotations. Image credit: ESA/Royal Observatory of Belgium

This montage of 366 images shows our Sun through the eyes of ESA’s Proba-2 satellite, as seen each day in 2016. The satellite’s SWAP camera works at extreme ultraviolet wavelengths to capture the hot turbulent atmosphere of the Sun, known as the solar corona. Each image was created from 30 separate images centred on 01:00 GMT each day, which were processed to enhance the features extending from the solar disc. Throughout 2016 the Sun’s 11 year activity cycle continued towards its minimum, a period when the number of sunspots, active regions, solar flares and eruptions diminish. Nonetheless, the most active region of last year can be seen in the 17 July image. The bright region close to the centre of the Sun produced eight of the 20 most powerful flares witnessed last year. Other prominent features are coronal holes – darker regions indicating lower levels of emission. However, coronal holes can produce streams of fast solar wind that can trigger geomagnetic storms on Earth. One of the largest holes observed last year can be seen towards the north of the Sun on 24 November, and was present for several solar rotations. Image credit: ESA/Royal Observatory of Belgium

Originally posted on Forbes!

Sound is a tricky thing in space. Sound is a pressure wave, an oscillation in the density of air or water, which moves through the air or through water until it reaches something it can rattle. If that sound is reaching a human ear, and if the oscillation is within the range of frequencies we are sensitive to, it will be heard. Our Earth produces a number of these pressure waves, from the sound of a person next to you speaking, or the crash of a wave on a beach, or a sonic boom of an airplane above you. However, there are plenty of sounds produced which we are outside our range of hearing - with an instrument tuned to receive those pressure waves, we can prove their presence, but it would be impossible to play back and hear it without speeding up the recording.

In space, we have a major problem with recording sounds; there’s no atmosphere for sound waves to travel through, so any pressure waves an object may be producing will be instantly silenced without a medium to compress. However, if you’re clever about it, there are other ways of recording information which can be translated into a sound; the easiest one is vibrations. The ‘crunch’ of Philae, Rosetta’s lander on the comet 67P, hitting the surface of the comet made the rounds - but this noise is not, in fact, the result of a microphone on the landerThis noise is a translation of the vibrations of the feet of the lander at the moment when it hit the surface of the comet.

Rosetta’s lander Philae has been identified in OSIRIS narrow-angle camera images taken on 2 September 2016 from a distance of 2.7 km. The image scale is about 5 cm/pixel. Philae’s 1 m-wide body and two of its three legs can be seen extended from the body. The images also provide proof of Philae’s orientation. A Rosetta Navigation Camera image taken on 16 April 2015 is shown at top right for context, with the approximate location of Philae on the small lobe of Comet Churyumov-Gerasimenko marked. Main image and lander inset: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA; context: ESA/Rosetta/NavCam, CC BY-SA IGO 3.0

Rosetta’s lander Philae has been identified in OSIRIS narrow-angle camera images taken on 2 September 2016 from a distance of 2.7 km. The image scale is about 5 cm/pixel. Philae’s 1 m-wide body and two of its three legs can be seen extended from the body. The images also provide proof of Philae’s orientation. A Rosetta Navigation Camera image taken on 16 April 2015 is shown at top right for context, with the approximate location of Philae on the small lobe of Comet Churyumov-Gerasimenko marked. Main image and lander inset: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA; context: ESA/Rosetta/NavCam, CC BY-SA IGO 3.0

However, if you want to translate a data set into sound, you’re not limited to just dealing with vibrations. You can turn pretty much anything into a set of tones, if you’re creative enough. Sonification is a booming area of data manipulation -- it’s another face of the data visualization scene; instead of presenting the information visually, you can code it audibly, and listen to it over time. You simply have to decide what you want the pitch of the musical note to correspond to, what you want the timing between each note to correspond to, and what you want the volume to correspond to.

For data coming from a spacecraft which monitors the Sun, there is often a new image every hour and a half or so. In this case, the pacing between notes is easily given to the time between observations, which will form a regular cadence. However, extracting a volume and pitch out of the data will depend very much on exactly what part of the data you’re interested in reflecting.

For Rosetta’s “singing comet” sonification, there was a very low frequency oscillation in the magnetic field surrounding the comet, measured by Rosetta. The decision here was to use the frequency of that vibration in the magnetic field as the pitch, but sped up by a factor of 10,000, so that it could register in the human ear. The volume here is driven by how large the oscillations were, much as it would be for a sound wave on Earth.

Single frame enhanced NavCam image taken on 27 March 2016, when Rosetta was 329 km from the nucleus of Comet 67P/Churyumov-Gerasimenko. The scale is 28 m/pixel and the image measures 28.7 km across. Image credit: ESA/Rosetta/NavCam – CC BY-SA IGO 3.0

Single frame enhanced NavCam image taken on 27 March 2016, when Rosetta was 329 km from the nucleus of Comet 67P/Churyumov-Gerasimenko. The scale is 28 m/pixel and the image measures 28.7 km across. Image credit: ESA/Rosetta/NavCam – CC BY-SA IGO 3.0

For the Sun, not only do we have to speed up the oscillation, but we also have to choose which observed oscillation we want to convert into a sound. The most common choice that I found was to examine the roiling surface of the Sun, which resembles nothing more than a pot of water at high boil. You could imagine examining how high the bubbles rise above the surface, and how quickly they do so. If we convert this amplitude and rapidity into a volume and a tone, we can get a musical note out for every bubble that rises to the surface. This is only one of many possible optionsfor sonifying the Sun, but it seems to be one of the more common choices.

What do we hear? Here’s a few examples.

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