Double Rainbow

Nijū no niji | DSC-RX1 | 1/250s f/11.0 ISO100 35mm 

(click the photo for full-screen)

This morning was one of my least favourite kinds of weather - sideways rain due to strong winds. The umbrella is merely used for its placebo effects. The sun broke through the clouds at around 5pm, with sunset due at 5:27pm (so early in Tokyo). As I walked past one of the labs, I noticed an amazing colour in the sky, and made a dash for the emergency fire escape - to be treated by a view like no other... a double rainbow (二重の虹) over Tokyo Sky Tree. I switched my camera to manual mode, as I wanted maximum detail and control over the exposure. The above is the result of a 3-photo vertical stitch, as the arc was just too wide. I think I've probably got an opening slide for the next presentation I give on atmospheric aerosols!

Info: Secondary rainbows are caused by a double reflection of sunlight inside the raindrops, and appear at an angle of 50–53° (a single rainbow is at 42º). As a result of the second reflection, the colours of a secondary rainbow are inverted compared to the primary bow, with blue on the outside and red on the inside. 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. The dark area of unlit sky lying between the primary and secondary bows is called Alexander's band.