A working three-dimensional model of the Sun's helical voyage through the Milky Way, sounded by a generative engine. Eight planets, ten of their moons, the asteroid and Kuiper belts, the galactic plane in the distance. The Sun does not sit at a centre; it travels through the galaxy at roughly two hundred and thirty kilometres per second, and the planets, dragged along, corkscrew behind it.

The work

Helioscope runs in real time. Planets corkscrew behind the Sun. Moons trace cycloids around the planets. The asteroid belt smudges through the gap between Mars and Jupiter; the Kuiper belt glows cold at the far edge. A year passes in about thirty seconds at the default tempo. You can pause it, speed it up, or just sit; the simulation has no end state to arrive at.

The sound

Every body's motion is sonified. A planet plucks a note when its orbit sweeps past a fixed angle, and its moons add finer plucks an octave above. Mercury rings every several seconds. Neptune only every several minutes. Underneath, a long drone holds the room. All of it sits inside a convolution reverb deep enough that the bells never quite stop ringing.

The piece is meant to play for hours. There is no track length and no loop; the score is whatever the planets happen to be doing.

Tuning

The piece is in F Lydian — the mode of the major scale with a raised fourth degree. Schubart, in his 1780s catalogue of keys, called F major the key of "complaisance and calm." The Lydian raised fourth opens that calm outward into wonder, the awe of looking up at a clear sky. Still warm, still settled, but reaching. Adjacent scale degrees are close enough together that any combination of bells ringing at once stays consonant — a structural choice for a piece intended to run for hours.

Each planet takes one degree of the scale, descending with distance from the Sun. The eight degrees ride from D5 down to D4 — D, C, B, A, G, F, E, D. Earth sits on the raised fourth (B), the Lydian "colour" note that gives the mode its open character. Saturn anchors the tonic (F). Each moon plays an octave above its parent, glittering in the brighter register. Underneath everything is a drone on the tonic F plus its fifth C and the octave above — quiet enough that you don't really hear it as melody, more as warmth.

There is no meter. The orbital periods of the planets are not in whole-number ratios with one another — they can't be, physically — so the pulse that emerges never repeats. Mercury rings every few seconds, Neptune every few minutes. Occasionally two bells nearly coincide and you hear a brief alignment; then the orbits drift apart and that arrangement is gone for good.

Each note is synthesised additively, as a stack of detuned sines — a fundamental plus quieter partials at inharmonic ratios. The classical 2.76 ratio sits in there, the one that gives a struck metal vessel its bell character. Attack slow, decay long, upper partials darker than the bottom. Through the convolution reverb the strikes overlap into a wash that almost never empties.

Each planet has its own voice. Mercury rings as a small crystal bell, sharp and bright; Venus as a singing bowl, slow to wake; Earth as a classic temple bell; Mars as a clangorous iron one. The gas giants are larger instruments: Jupiter a deep gong whose low partials beat against each other, Saturn a dry wooden marimba bar that stops almost as soon as it sounds. The ice giants change register entirely — Uranus a glass armonica, slowly bowed; Neptune a cast church bell with a sub-octave hum tone underneath, the longest-sustaining voice in the piece. With your eyes closed you should be able to tell which planet just rang.

Solar weather

The Sun is not still inside the room either. Sunspots — dark patches where the magnetic field punches through the surface — sit at real heliographic positions, the ones NOAA's Space Weather Prediction Center is reporting today. They drift slowly across the disc as the Sun rotates beneath them.

Occasionally one of them flares. A flare is a sudden release of stored magnetic energy; in the image it shows as a brief whole-disc flash, and in the music as a deep gong and a long opening of the drone. The flares are real: every X-ray event GOES-18 has detected in the last seven days is replayed on a one-hour loop, with each event's class — B, C, M, or X — setting how loudly the gong rings.

A fraction of flares throw a coronal mass ejection — an expanding cloud of plasma launched outward at a few million kilometres an hour. The model includes them as turbulent fronts ballooning from the active region. When one reaches a planet, two things happen: the planet briefly haloes in aurora-blue, its limb brightening as if its magnetosphere were compressing under the wave; and the room rings with that planet's bell at gallery volume — Earth or Mars or Jupiter struck on the chime, exactly as the actual particles would arrive a day or two later.

Spaceship Earth

The piece is, in the end, a portrait of a ship. Earth, and us with it, moves through the Milky Way bound to a star. The Sun is the engine of that journey and also its shield: photosynthesis runs on it, the weather runs on it, and the Sun's magnetic field blows the heliosphere out past Pluto and keeps interstellar cosmic rays from sterilising the inner planets. Pull the Sun from the diagram and there are no orbits anywhere; the planets cool, they go dark, and the thing falls apart.

The other bodies are working too. The Moon's tide stabilises the oceans and pins Earth's axial tilt; without it the climate would walk. Jupiter has spent four billion years using its gravity to sweep comets out of the inner system — a quiet bouncer for the rocky worlds. Earth's own magnetic field deflects the solar wind it sits inside. Nothing in the system is incidental; every body is part of what keeps the cradle habitable.

Buckminster Fuller, nearly sixty years ago, called this Spaceship Earth — a single closed vessel with no spare parts. The crew is now about eight billion. Helioscope is one way of seeing the vessel: the Sun pulling forward, everything else dragged along after it.

Two engines

Helioscope can be heard in two ways. The default is the browser engine — synthesis is internal, mixed to your speakers or headphones. An alternate analog engine silences the internal voices and emits eight DC control signals through the audio device's outputs: pitch at one volt per octave, gate, velocity, two slow LFOs derived from the simulation, and three per-group trigger gates. Patched into an outboard analog rack, the geometry plays the room.

The piece in the practice

Joshua Borsman is an artist and engineer. His work treats physical phenomena — tides, gravity, telemetry, light — as collaborators rather than subject matter, and the pieces are usually instruments built to make those phenomena audible or visible at human scale.

Helioscope is one of those instruments. Its score is the geometry of the solar system; the composer is gravity. The orbital periods of the planets don't fall into whole-number ratios with one another, so the rhythm they make can never loop, and the Sun's motion through the galaxy runs a single slow line under everything. Nothing in the piece is invented. The pitches, the cadence, the silences between rare deep tones — all of it is the solar system, watched and listened to for long enough.

The work joins a small group of Borsman's pieces in which a celestial or temporal system is made audible: a telescope tuned to a stellar spectrum, a string plucked when the International Space Station passes overhead, a pendulum tracing the figure of its own decay. In Helioscope, the system being made audible is the solar system itself.

Materials

Image

WebGL · custom fragment shaders for the Sun, planets, and nebula

Sound

Web Audio · synthetic convolution impulse · DC sources for control voltage

Analog interface

Browser audio routed to a DC-coupled multichannel audio device · eight channels of control voltage

Orbital data

NASA JPL ephemerides · real periods, distances, and inclinations · visual scaling compressed for legibility

Solar data

NOAA Space Weather Prediction Center · live sunspot positions and GOES X-ray flare events · 7-day window replayed on a one-hour loop

Duration

Continuous · generative · non-repeating

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