Tonight on BBC4, a unique piece of music will be broadcast. Commissioned by the BBC, in association with the Minnesota Orchestra, Deep Field is a 25 minute-long soundscape of epic ambition. It was recorded on Sunday 9 August at its European premiere, as part of the BBC Proms 2015 at the Royal Albert Hall.

Hubble at 25: the space telescope's timeline - in pictures Read more

As Whitacre explained in his introduction at the concert, he was inspired by the Hubble Space Telescope’s historic image, the Hubble Deep Field. Taken over a 10-day period between 18-28 December 1995, the image is the result of a 342 separate images taken of the same region of sky.

The region was tiny, just one-twelfth the width of the full moon, yet Hubble revealed around 3000 distant collections of stars. These galaxies are among the furthest we have ever seen. They are so far away that their light has taken more than 10 billion years to reach us, meaning that we were seeing them as they appeared in the infancy of the Universe.

The Hubble Deep Field revolutionised the study of the early universe, a realm that we had never seen before. Given its importance to astronomy, it seems fitting that someone should write a piece of music about it.

Facebook Twitter Pinterest The historic Hubble Deep Field image. Photograph: Robert Williams and the Hubble Deep Field Team (STScI) and NASA

Music and astronomy have a long history of association. It stems from the identification that musical pitch can be related to the length of a plucked string. Therefore a musical interval between two notes can be expressed as a mathematical ratio between the lengths of two strings. Following this realisation, 6th century BC philosopher Pythagoras wondered whether the movement of the planets could be understood in terms of similar ratios.

Each celestial body was at a different distance from the Sun, and moved across the sky at different speeds. So Pythagoras postulated that each planet “emitted” a different hum and together these notes made up the musica universalis, often referred to as the harmony of the spheres.

In the 17th century, German astronomer and mathematician Johannes Kepler picked up the baton. He discovered that the key to understanding planetary motion was that instead of all moving in circular orbits at constant speeds, most planets followed elliptical paths and varied their speed as they went.



He recast the harmony of the spheres as a series of scales in which the musical intervals for each planet were dictated by its range of speeds. Venus, which does follow a circular path, could only sing one note. The Earth, with its almost circular path could sing two notes, separated by a semitone.



Kepler identified these as the major-third and the perfect fourth, Mi and Fa. Ever the optimist, he said this was because misery and famine held sway on Earth. Charming. Mercury and Mars, with their more elliptical orbits had a much greater range of notes to emit. (See The Harmony of the World, page 439 for musical notation, or the video below)

The register of each planet was governed by its average speed, in other words its distance from the Sun. This gave Kepler his celestial choir: Mercury (soprano), Venus and Earth (altos), Mars (tenor), Jupiter and Saturn (basses). The YouTube video below is an example using keyboards of what Kepler’s harmony of the spheres sounds like.

Facebook Twitter Pinterest An modern interpretation of Kepler ‘s harmony of the spheres.

There were times when Whitacre’s Deep Field sounded somewhat similar to this shifting soundscape, with simple phrases building on top of one another. But the best part of the performance was saved for last.

About twenty minutes into the piece, the Royal Philharmonic Orchestra built to a shimmering crescendo. As the music died away, so too did the lights. Soon, there was nothing more than a moonlight glow in the concert hall, and the members of the BBC Symphony Chorus and BBC Singers filed silently down the seven walkways into the auditorium.

Once in position they sang repeating pairs of chords that matched the beauty of the Hubble Deep Field, which spontaneously appeared on audience members’ smart phones. This latter was the result of the Deep Field app that we had downloaded beforehand and triggered on cue from the conductor. The app also emitted faint electronic sounds that filled the night-time ambience of the hall, allowing the choral voices to float on top.

The contribution from the chorus has been likened to that heard in Gustav Holst’s Neptune from the famous Planets Suite. But this is not a criticism. Each generation of astronomers has built on the work of the last, reinterpreting and refining. So, why not echo that tradition in music inspired by astronomy?

Deep Field will be broadcast as part of Prom 32 at 19:30 BST on Friday 14 August on BBC4.

Stuart Clark is the author of The Sky’s Dark Labyrinth (Polygon). He is teaching the Guardian Masterclass, How the Universe Works in September.