What causes ball lightning -- the rare glowing, floating orbs of light, sometimes seen after ordinary lightning strikes, that can persist for seconds and even pass through windows or walls?
Under some conditions, does a container of initially hot water actually freeze to ice sooner than an otherwise identical container of initially cooler water, and if so, why?
Why does an airplane passenger or mountain hiker sometimes see concentric colored rings of light (a 'glory') surrounding the shadow of their own head, cast on clouds or fog directly opposite the sun?
Why did the newly opened Millennium footbridge in London begin swaying alarmingly from side to side as soon as a crowd walked across it, even though it had been engineered to withstand pedestrian loads?
Why do certain desert sand dunes emit a loud, sustained booming or humming sound (sometimes audible for miles) when sand cascades down their slope, while most sand dunes and beaches stay completely silent when disturbed?
When a tiny gas bubble trapped in water is driven to violently collapse by a sound wave, why does it emit a flash of light -- and why is the exact mechanism that produces that light still debated among physicists?