Music of the spheres
ANDREW MAY explores the celestial harmonies of Johannes Kepler and their modern-day revival in musical-astronomical collaborations.
Johannes Kepler lived at the same time as Galileo, and shared his interest in planetary motion. His contributions to the field were significant enough for NASA to name its first planethunting space telescope after him. But while Galileo had the materialistic viewpoint of a modern scientist – and famously got into conflict with the Church – Kepler saw things in a completely different way.
From 1601 to 1612 his official position was Imperial Mathematician to the Holy Roman Emperor Rudolph
II – which sounds scientific enough, until you recall Rudolf’s obsession with the occult (he was also a patron of Edward Kelley and John Dee). For Kepler, there was no incompatibility between the scientific and the mystical, as his biographer David Love writes: “These two aspects of his work were always an integrated whole... he was taking a single unified approach to nature, which he saw as the creation of a mathematically motivated
1 deity.”
This comes across as clearly as anywhere in Kepler’s work on the “music of the spheres”. Even in his own time this was an old concept, going back to the Ancient Greek philosophers. To them, the planets really did revolve on invisible spheres – centred on the Earth rather than the Sun – and they believed that these spheres were arranged in simple ratios analogous to strings vibrating in musical harmony.
Like Galileo, Kepler understood that the planets go round the Sun rather than the
Earth. He also knew that sound is a wave that travels through air, with musical pitch being governed by the frequency of oscillation. In modern terms, frequency is measured in hertz, or oscillations per second. The piano keyboard, for example, spans approximately 30 to 4,000 Hz. But any regularly repeating cycle can be measured in hertz – even the Earth’s orbit around the Sun, which takes a year to complete. With a frequency of just 32 nanohertz, that’s much too low to hear – but at least it gives a tenuous validity to the concept of a “music of the spheres”.
Thinking along these lines, Kepler transformed the notion from the literal sound imagined by the ancient Greeks into an intellectual abstraction. In his own words, “the celestial motions are nothing else than a continuous heavenly music which can be perceived only with the mind, not with the ear.” That’s a quote from his book Harmonices Mundi (“Harmony of the World”) dating from 1619. Although it’s padded out with a lot of mystical speculation, the book has an important place in the history of science because it’s where Kepler formulated the last of his three laws of planetary motion. The first stated that planets move around the Sun in elliptical orbits, not circular ones, while the other two describe how a planet’s speed varies around its orbit, and from one planet to another.
We now know that these laws are unavoidable consequences of the way gravity works, but for Kepler they were simply part of the creator’s design spec for the Solar System. Obviously, there was some rationale behind them, so why not a musical one? His three laws described how planetary speeds vary in the course of an orbit, and from that he could determine the corresponding frequency (which likewise varies over time). He then arrived at his version of the music of the spheres – which he wrote out in standard notation – by scaling those frequencies up into the audible range.
It’s an interesting exercise
– and one that scientist John
Rodgers and musician Willie Ruff repeated using modern data in 1979. They chose their scaling factor so that Earth’s average frequency – the 32 nanohertz mentioned earlier – translates to 800 Hz in the audible range. But it’s not a constant tone, because the ellipticity of the Earth’s orbit means the frequency wobbles by roughly a semitone – from G to G-sharp in Rodgers and Ruff’s system. Kepler discovered this semitone wobble too, which he interpreted as an oscillation between the notes mi and fa in the do-re-mi system. Since nothing happened by accident in Kepler’s worldview, this obviously conveyed some important message from the Creator. “The Earth sings mi-fa-mi,” he wrote, “so that even from the syllables you may guess that in this home of ours misery and famine hold sway.”
The other planets play tunes of their own: the inner ones, Mercury and Venus, at higher frequencies and the outer ones – only Mars, Jupiter and Saturn being known in Kepler’s time – at lower frequencies. The last two are particularly interesting, as Rodgers and Ruff point out:
“Jupiter’s song covers a minor third, from D down to B just below the bass staff. Still farther
“A continuous heavenly music which can be perceived only with the mind”
out and still lower is Saturn. Its range is a major third, from B down to G, the B at the top being just an octave below the B at the bottom of Jupiter’s range. Thus the two planets together define a major triad, and it may well have been this concord that made Kepler certain he had cracked the code and discovered the secret of the celestial harmony.”2 (This may sound cryptic to nonmusicians, but it’s just saying that the notes G, B and D make up the harmonious chord of G major).
In Kepler’s time, planetary motions were the only regularly repeating phenomena known in astronomy. Since then, many other examples have been discovered – on a vast range of frequencies from far below the audio spectrum to far above it. By applying the same scaling procedure, any of these can be converted into a modern-day “music of the spheres”. The process has become so wellestablished – among space geeks at least – that it’s been given a formal name: astronomical sonification.
One of the most widely heard examples was produced by the European Space Agency in 2014, as part of its social media blitz during the Rosetta mission to comet 67P. Called “The Singing Comet”, this particular sonification was based on oscillations in the comet’s magnetic field. Occurring at very low frequencies between 40 and 50 millihertz, these were scaled up by a factor of 10,000 to make them audible. The result received almost six million listens on SoundCloud, and was widely reported by news outlets around
3 the world.
Another potential source of outer space sounds is radio astronomy – an obvious one, given the use of radio for sound broadcasting on Earth. In fact, the sonification of radio signals has more than entertainment value, since it can be used alongside visualisation as an aid to data analysis. In this context, the science of “acoustic astronomy” was created by Fiorella Terenzi, when she was working on her doctoral thesis at the University of California in 1987. She used
a computer sound synthesis program – still quite a novelty in those days – to convert radio telescope data from the galaxy UGC 6697 into audible form.
Now a professor at Florida International University, Terenzi has applied the same technique to many other astronomical phenomena, ranging from the Sun and the planets Jupiter and Saturn to distant pulsars, quasars and X-Ray binaries. You can hear a selection of samples on her
4
website.
It’s a bit of a stretch to describe the sonifications we’ve met so far as “music” – but some people have taken the idea a step further. In 2011, astronomers Alex Parker and Melissa Graham produced a
Supernova Sonata based on data from 241 supernova events, with all the musical elements – pitch, volume, instrumentation and so on – determined by different
5
astrophysical parameters.
The following year a similar exercise was reported on a NASA blog, this time using data from a gamma ray burst, which was converted into music by Sylvia
6
Zhu. Each gamma-ray photon was scaled down from its original, enormously high, frequency to the audible spectrum, with the rate of arrival of photons also
slowed down to a sensible tempo.
Although the results sound interesting enough, such efforts by members of the scientific community are more likely to have novelty than aesthetic value. But a few professional musicians have got in on the act too. Thomas Dolby, for example, used input from Fiorella Terenzi on his 1994 album The Gate to the Mind’s Eye, while the reggae band Echo Movement used data from the Kepler space telescope on Love and the Human Outreach (2012). And FT editor David Sutton drew my attention to extensive work in this area by former Grateful Dead drummer Mickey Hart.
In 2013, Hart teamed up with cosmologist George Smoot of the Lawrence Berkeley Laboratory in California. A few years previously, Smoot had won the Nobel Prize for his work on the cosmic microwave background (CMB) – the oldest radiation in the Universe, which Hart describes as “beat one”.7 The collaboration resulted in a 20-minute audiovisual experience called Rhythms of the Universe, first mounted at the Smithsonian Air and Space Museum in Washington, DC. Taking Smoot’s data on the CMB as a starting point, Hart worked with Lawrence Lab scientists to combine it with other astronomical data – from the Sun, pulsars and distant galaxies – and convert it into something that actually sounds like music (Hart admits he took some artistic liberties with the scientific data to produce the sound he wanted).
Hart made a second foray into astronomical sonification in April 2018, this time for an event called Musica Universalis at the Hayden Planetarium in New York. That title – Latin for “Music of the Universe” – is a virtual synonym of Kepler’s “Harmony of the World”, and Hart seemed to echo Kepler’s worldview in an interview he gave at the time:
“Music is vibrations, which are an essential part of life, but are also an essential part of the Universe. We’re just a miniature of what’s happening in the cosmos... the Universe is one giant instrument played by the forces of nature. And that’s what Musica Universalis is all about. It’s
8 the greatest story ever told.”
NOTES
1 David K Love, Kepler and the Universe, Prometheus Books, New York, 2015, p. 163
2 John Rodgers & Willie Ruff, “Kepler’s Harmony of the World: A Realization for the Ear”, American Scientist, May-June 1979, p. 292
3 Emily Baldwin et al, Communicating Astronomy with the Public, issue 19 (March 2016), pp. 33-4
4 Fiorella Terenzi, “Acoustic Astronomy: The Sounds of the Universe”, http:// faculty.fiu.edu/~fterenzi/research/
5 Alex Harrison Parker, “Supernova Sonata”, http://www.astro.uvic. ca/~alexhp/new/supernova_sonata.html
6 Julie McEnery, “The Sound of a Fermi Gamma-Ray Burst”, https:// blogs.nasa.gov/GLAST/2012/06/21/ post_1340301006610/
7 Natasha Geiling, “Former Grateful Dead Drummer Mickey Hart Composes Music from the Sounds of the Universe”, https://www.smithsonianmag.com/ science-nature/former-grateful-deaddrummer-mickey-hart-composes-musicfrom-the-sounds-of-the-universe-265907/
8 Sam D’Arcangelo, “Mickey Hart Talks Sounds of the Universe”, https:// liveforlivemusic.com/features/mickeyhart-sounds-universe/
2 ANDREW MAY is a freelance writer and defence consultant and a regular contributor to FT. His latest book is The Science of Sci-Fi Music (Springer, 2020).