Teatime Optics by Serge Stepanenko of the Crimean Astrophysical Observatory (CrAO),Crimea, Ukraine. ©Serge Stepanenko, shown with permission.

Iridescence above a tea cup. Water vapour evaporated from the hot tea mixes with cool air and condenses into the droplet clouds we call 'steam'.

The small droplets diffract light to produce iridescent colours. Serge has backlit the cup to show them to best advantage. The same colours are seen over hoar frost subliming in warm sunshine, sun warmed damp wood and of course clouds.

Optical effects surround us. While contemplating tea or coffee time iridescence look also for caustics on the liquid surface produced by reflections from the curved cup walls. Sit the cup in the sun and watch reflections from the liquid dance on a wall or ceiling - experiment with different taps on the table to change the liquid vibration modes.


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