Natural Satellite
for guitar duo (2013)
duration: 22’
GRT • 164
score available from
Australian Music Centre
program note
A natural satellite, moon, or secondary planet is a celestial body that orbits a planet or smaller body, which is called its primary. Earth has one large natural satellite, known as the Moon. No “moons of moons” (natural satellites that orbit the natural satellite of another body) are known. In most cases, the tidal effects of the primary would make such a system unstable. The seven largest natural satellites in the Solar System are Jupiter’s Galilean moons (Ganymede, Callisto, Io, and Europa), Saturn’s moon Titan, Earth’s moon, and Neptune’s captured natural satellite Triton.
I: The gravitational influence of Titan
Most regular moons in the Solar System are tidally locked to their respective primaries, meaning that the same side of the natural satellite always faces its planet. The only known exception is Saturn’s natural satellite Hyperion (the first non-round moon to be discovered), which rotates chaotically because of the gravitational influence of Titan. The 3:4 orbital resonance between Titan and Hyperion may also make a chaotic rotation more likely.
II: The moons of Jupiter
The planet Jupiter has 67 confirmed moons. The most massive of them, the four Galilean moons, were discovered in 1610 by Galileo Galilei and were the first objects found to orbit a body that was neither Earth nor the Sun. This incontrovertible discovery dealt a serious blow to the prevailing geocentric theory that everything orbited around the Earth. The three inner moons – Ganymede, Europa, and Io – participate in a 1:2:4 orbital resonance.
III: Triton Captured
Triton is the largest moon of the planet Neptune. It is the only large moon in the Solar System with an orbit in the opposite direction to its planet’s rotation, and consequently thought to have been captured from the Kuiper belt.
IV: Within the rings of Saturn
Small bodies have been observed within rings of Saturn, but only a few were tracked long enough to establish orbits.
V: Earth’s Moon
The Earth–Moon system is unique in that the ratio of the mass of the Moon to the mass of the Earth is much greater than that of any other natural satellite:planet ratio in the Solar System. Our Moon makes Earth a more liveable planet by moderating our home planet’s wobble on its axis, leading to a relatively stable climate, and creating a rhythm that has guided humans for thousands of years.