August 7 - 13, 2016: Issue 275

Double Rainbow

Photo by Bernadette Kelly, Friday August 5th

These great photos by a local student were taken at Avalon Beach on Friday afternoon. We all know it's been a but cold and damp this week, lots of snow for those who love skiing or tobogganing , and lots of rain for ducks to go paddling in.

Among all the showers there have been bursts of sun, which can make rainbows.

A double rainbow, or secondary rainbow, is caused by a double reflection of sunlight inside the raindrops, and are centered on the sun itself. They are about 127° (violet) to 130° (red) wide. Since this is more than 90°, they are seen on the same side of the sky as the primary rainbow, about 10° above it at apparent angles of 50–53°. As a result of the "inside" of the secondary bow being "up" to the observer, the colours appear reversed compared to the primary bow. The secondary rainbow is fainter than the primary because more light escapes from two reflections compared to one and because the rainbow itself is spread over a greater area of the sky. Each rainbow reflects white light inside its coloured bands, but that is "down" for the primary and "up" for the secondary. The dark area of unlit sky lying between the primary and secondary bows is called Alexander's band, after Alexander of Aphrodisias who first described it.

Alexander of Aphrodisias was a philosopher and teacher. The term "philosopher" comes from the Ancient Greek word (philosophos) meaning "lover of wisdom". Its origination has been ascribed to the Greek thinker Pythagoras.

Alexander lived and taught in Athens at the beginning of the 3rd century, where he held a position as head of the Peripatetic school. 

The school originally derived its name Peripatos from the peripatoi (Greek  "colonnades") of the Lyceum in Athens where the members met. A similar Greek word peripatetikos refers to the act of walking, and as an adjective, "peripatetic" is often used to mean itinerant, wandering, meandering, or walking about. 

Thanks Bernadette - great snap!