Hexagonal cloud cells in the South Atlantic Ocean

Here we see an arrangement of hexagonal clouds photographed by the Moderate Resolution Imaging Spectroradiometer (MODIS) sensor aboard the Terra satellite on 6 June, 2002.

These formations are produced by Rayleigh-Bénard convection, and constitute a good example of how thermodynamic systems often self-organize into hexagonal structures as a consequence of roughly circular regions of force pressing against or pulling away from each other, effectively generating Voronoi diagrams from a lattice of circular (or cylindrical) cell centers.

(This phenomenon is, presumably, wholly unrelated to the well-known Saturn hexagon, though both clearly demonstrate the tendency of self-organizing systems to prefer hexagonal configurations over lesser geometries.)