Mars in Retrograde, commissioned by Kat Anderson and dedicated to The Los Angeles Belles, is a 3-part vocalise for SSA and Piano based on planetary motion and gravitational orbits. The voices represent the orbits of the planets (S1 as Venus, S2 as Earth, and Alto as Mars) around the sun, which is represented by the Piano. Each planet (voice) has a distinct repeating rhythmic pattern whose length corresponds to each planet’s sidereal period (how long it takes the planet to fully orbit around the sun). The repeating rhythmic pattern uses the musical technique of isorhythm, where a repeating rhythmic pattern (called the talea) is combined with separate pitch material (called the color). Venus’s sidereal period is roughly .616 Earth years, corresponding to a 7.5 measure talea. Earth’s sidereal period is 1 Earth year, corresponding to a 12 measure talea (based on the 12 months in a year). Mar’s sidereal period is roughly 1.9 Earth years, corresponding to a 22.75 measure talea. The rhythmic activity increases until the mid-point of each talea, after which the rhythmic value decreases again. This represents how planets increase in speed as they approach their closest point to the sun (perihelion) and decrease in speed as they approach the farthest point from the sun (aphelion).
The entire piece is tuned to the fundamental of Bb, as the lowest recorded note in the universe is a black hole that vibrates at a Bb 57 octaves below Middle C. The piece exclusively uses the Bb Lydian Dominant scale, also referred to as the acoustic scale, which can be created by assembling the first 12 partials of the overtone series based on the fundamental of Bb.