= Tidal locking
{wiki}
<Tidal locking> settles a body's spin into a sustained relation with its orbital motion through <tidal forces> and <tidal dissipation>. The simplest case is <synchronous rotation>, a $1:1$ <spin-orbit resonance>. On an ideal <circular orbit>, with spin axis perpendicular to the <orbital plane>, the body keeps the same face toward its companion, as the <Moon> approximately does toward <Earth>. https://science.nasa.gov/moon/tidal-locking/[Tracy Vogel, NASA: tidal locking]{ref}.
This article retains the broader sense of <tidal locking> as capture into a <spin-orbit resonance>; the term is also commonly used specifically for <synchronous rotation>. Tidally evolved rotation need not be $1:1$: <Mercury> has a $3:2$ <spin-orbit resonance> with the <Sun>, turning three times in two <orbital periods>. The distinction matters when inferring illumination or climate from a spin period. https://arxiv.org/pdf/1209.1580[Rodríguez et al. (2012): spin-orbit coupling]{ref}.
Back to article page
