I was sitting by a window, rereading some of the short chapters that make The Hidden Life of Trees so easy to follow and enjoy. It had been raining hard throughout the night. The term ‘pelting’ had come to my sleepy mind as gusts of wind drove the raindrops onto our windows, sounding like the huge hail that sometimes makes us doubt the strength of glass.
Throughout the night, the rainwater that collected on the flat roof of our bedroom was being sluiced off in sheets that pounded percussively on the skylights we put in the lower roof. It was hard to sleep through the noise.
Tired, the sun low in the sky this autumnal morning, I was reading and not paying much attention to the continuing gust driven rain, products of the forecasted squalls.
I noticed a rainbow had materialised to the north as I thought about wood and how twenty percent of all terrestrial life forms depend on it. Across Dublin Bay, beyond the rainbow, on Howth, there is always a white building at sea level that catches my attention. As I looked this time, it was touching the leading edge of the rainbow.
Next time I looked, the white building was behind the red-yellow transition. The rainbow intensity varied in the ever changing light conditions. It was luminous at times, so bright that I briefly considered getting a camera. But to get the camera was to lose the thread of the book. So I carried on reading. ‘There’s consensus among German politicians that 5% of the forest should be left to their own devices so that they can become the old-growth forests of tomorrow.’
When I next looked up, the coastal white house was coated in green-blue spectral colours. I watched for a few minutes and I could see the right hand arc of the rainbow move towards the east. Nothing new here, I thought. That’s because I regularly see the moon and the sun move as does anyone who tries to photograph either object with a big telephoto lens. Likewise for other celestial objects. Star trails will appear and can ruin night time exposures if you aren’t careful. Or make the photo, if that was your intention.
There’s a simple rule of thumb photographers call ‘500’. To avoid star trails with a static camera, you need to limit the exposure time. So photographers divide 500 by the focal length to determine the maximum exposure time (in seconds). Simply put, a 500 mm lens has a maximum exposure time of 1 second. That’s not enough time to gather sufficient light to make a picture without relying on the very high sensitivities that create unsightly artefacts. So astrophotographers tend to use much shorter focal lengths on static cameras. A 50 mm lens would allow you about 10 seconds. Use a 25 mm lens and the camera can gather starlight for about 20 seconds before the stars begin to blur.
I looked out again and saw the rainbow had moved further east and the white house down at sea-level was now bluish.
I jumped up and looked at a wider field of view. Arrghhh! I had just missed the photographic opportunity of a lifetime.
There had been a really bright double rainbow and I hadn’t realised I was looking at the outer, second rainbow. I hadn’t noticed it was ROYGBIV not VIBGYOR. The rainbow develops an outer arc by double refraction of the sunbeams as they pass through the raindrops and so the colour progression is inverted. If you know your mnemonics, especially in America, kids are often taught to recall Roy G Biv as the way to recall the colour spectrum. Red, orange, yellow, green, blue, indigo and violet. Of course, I went to boarding school where I was taught to never forget that Richard Of York Got Buggered In Venice.
I was looking at the rainbow as it faded and my opportunity to share a magnificent double arc to others was reduced to these words. Chinese mythology reckon that double rainbows are a sign of future success. I’ll take that.