Planetary orbits.
A planet's orbital period is just a frequency: cycles per second, far below human hearing. Take Earth's year — about 31.6 million seconds — and double it thirty-two times, and you land at 136.10 Hz. The same multiplier (232) is applied to every body in the solar system, so the orbital ratios are preserved exactly. Inner planets land squarely in the audible band; outer giants sit below 20 Hz and play as infrasonic keys — present, but felt rather than heard.
Each planet, its own pitch.
Pick a planet. The orbits are drawn to scale (logarithmically) — the relative spacing is real. The selected body's orbital frequency is divided in half until it reaches the audible band, and the readout shows you exactly how many octaves up that takes.
An orbit is a frequency.
Anything that repeats has a frequency. A pendulum. A heartbeat. A planet going around its star. Earth completes one orbit roughly every 3.156 × 107 seconds, which is the same as saying it has an orbital frequency of 3.169 × 10−8 Hz.
That's preposterously slow — far below anything we can hear. But every time you double a frequency you raise it by exactly one octave. Double Earth's orbital frequency thirty-two times — multiply by 232 ≈ 4.295 × 109 — and the result is ≈ 136.10 Hz, smack in the middle of a baritone's range. Thirty-one doublings would land an octave below; thirty-three would land an octave above. Thirty-two is just the integer that puts Earth squarely in the audible band.
The cosmic octave.
This idea was published by the Swiss mathematician Hans Cousto in The Cosmic Octave (1988). Cousto's insight wasn't astrological — he wasn't claiming planets cause these tones. He was making a mathematical observation: octave equivalence is a defined operation on any periodicity, so any periodic phenomenon, no matter the timescale, has a corresponding pitch.
Once you accept that, planetary tunings stop being mystical and become what they are: a precise, defensible mapping. Earth's year is 136.10 Hz, full stop. Mars sits just under an octave below at 72.36 Hz; Mercury, with the shortest year, lands at 565.09 Hz; Pluto sits below human hearing at 0.55 Hz. The ratios between any two of these match the orbital-frequency ratios exactly. Same MIDI notes. Different physics.
Halving a year.
Start with a planet's orbital period T in seconds. The orbital frequency is the reciprocal:
forbit = 1 / T
Then apply Cousto's octave-shift operator. The same integer N — the same multiplier 2N — is used for every body in the system, so the orbital ratios survive the transposition unchanged:
Eigentone picks N = 32 because that's the value that lands Earth at 136.10 Hz — the canonical "cosmic octave" Earth tone Cousto published in 1988. With that choice locked in, every other body follows: Mercury (the shortest year) jumps to 565.09 Hz, while Pluto (the longest) sits at 0.55 Hz, four-and-a-half octaves below human hearing.
Kepler's third law (T2 ∝ a3) means that knowing any planet's semi-major axis is enough to know its pitch — and conversely, every Eigentone planet note encodes a real distance from the Sun.
One multiplier for the whole solar system — about 49 710 Hz·days. Inner planets land in audio; outer giants stay infrasonic. The frequency ratios match the orbital ratios exactly, which is the entire point of uniform N.
Venus : T = 224.70 d → 221.23 Hz
Earth : T = 365.26 d → 136.10 Hz
Mars : T = 686.97 d → 72.36 Hz
Jupiter : T = 11.86 yr → 11.47 Hz · infrasonic
Saturn : T = 29.45 yr → 4.62 Hz · infrasonic
Uranus : T = 84.01 yr → 1.62 Hz · infrasonic
Neptune : T = 164.79 yr → 0.83 Hz · infrasonic
Pluto : T = 247.94 yr → 0.55 Hz · infrasonic
Periods from NASA NSSDC fact sheets (2020). Frequencies after Hans Cousto, The Cosmic Octave (1988); same uniform multiplier as dsp/FrequencyData.h.
What each key plays.
Nine keys, nine bodies — outermost on C, innermost on B. Neptune and Saturn ride the two black keys (C♯ and D♯). Pluto, Uranus, and Jupiter are real frequencies but sub-20 Hz: present, not heard.
Hear the solar system.
Planetary Orbits is in the free tier. Every white key is a real body's year, octave-shifted into your monitors.