Clouds form when moist air rises, expands and cools adiabatically until it reaches its dew point, causing water vapor to condense onto airborne aerosol and dust nuclei — cloud condensation nuclei. Puffy cumulus typically build in convective updrafts with cloud bases around 1–2 km, while towering cumulonimbus storm clouds can punch upward to 12–18 km, reaching the tropopause. A single cloud droplet is only about 10–15 microns across, invisible to the eye alone, but billions of them together scatter light as the white puffs seen here. Real time-lapse footage reveals this whole form-billow-dissipate cycle repeating every few minutes as pulses of convection rise and fade. Drag to orbit, scroll to zoom.