An Earth-observation satellite circles the planet about fourteen times a day, from pole to pole, while the Earth turns beneath it. Each orbit lays one thread across the map, a little to the west of the last. After sixteen days Landsat's threads close into a cloth and the pattern starts again exactly where it began. Its orbit is tilted so that Earth's equatorial bulge turns it once a year, in step with the Sun: every thread crosses the equator at the same local time, mid-morning, wherever it is.
Changing the altitude keeps the orbit sun-synchronous: the inclination follows from the altitude. Sound starts only when you press Sound: one note for each equator crossing.
The orbit. A circular orbit around an Earth with its equatorial bulge (the J2 term, 1.08263 × 10⁻³). The bulge makes the orbit's plane turn: Ω̇ = −(3/2)·n·J2·(R/a)²·cos i. Choosing the inclination so that Ω̇ matches the Sun's yearly motion, 360° in 365.2422 days, gives a sun-synchronous orbit: the guide's formula. The bulge also speeds up the satellite's motion around the orbit, u̇ = n·[1 + (3/4)·J2·(R/a)²·(8cos²i − 2)], which sets the nodal period, from one equator crossing to the next of the same kind.
The weave. Each point of the track is the satellite's direction from Earth's centre turned into latitude and longitude, with the Earth rotating underneath at 7.2921 × 10⁻⁵ rad/s (sidereal). Successive tracks cross the equator further west by the angle the Earth turns in one nodal period. The pattern repeats when a whole number of orbits fits a whole number of days, measured against the turning orbit plane: N·Tnodal = D·2π/(ωE − Ω̇). Snap solves that for the altitude. Sentinel-2's 143 orbits in 10 days come out at 786.1 km, its published altitude. Landsat's 233 in 16 give a semi-major axis of 7,077.7 km, which is how Landsat's orbit is specified; the familiar "705 km" is the height above the ground near the equator rather than above the 6,378 km reference radius used here. The gap between neighbouring tracks at the equator, 2πR/N, is Landsat's 172 km between paths.
Local time. The orbit plane is set so the descending crossing of the equator (heading south, on the day side) happens at the chosen local mean solar time. The Sun's position and the day–night line come from a standard low-precision solar formula; the night side is shaded.
Coverage. The swath, the strip the instrument sees, is painted onto a coverage map as the satellite moves; the percentage is the painted area weighted by the cosine of latitude, within the latitudes the swath can reach.
A data sculpture in the language of weaving: one thread at a time, the newest bright and the older ones fading, a cloth that only shows its pattern when the cycle closes. It recreates no specific work.