Radical Rayleigh Sunset

By the time I noticed this spectacular sunset it was too late to switch to my wide-angle lens, so I started shooting with my stock 18-55 mm. My first thought was to capture a set of overlapping images and stitch them into a sunset panorama. But that requires downsampling to fit the panorama on this page, or horizontal scroll bars to drag it around, so I decided to just compose for a slide show. There’s some interesting cloud structure in this display, typical of altostratus undulatis (commonly known as “wind-row clouds”). I kept shooting till the colors started to fade and the waves began to dissipate.

The date was Feb 16, 2018. A small storm system had dropped a little rain and was on its way out. The intense reddish colors you see in the slide show appeared and faded in the space of some 15 minutes (note the time stamps on the slides). It was what I call a “fast sunset.” I’ve done several posts featuring Arizona sunsets and explained the colors as a result of Rayleigh scattering, so I won’t dwell on any of the physics here. I just wanted to share my photos of this recent display.

My camera was on full auto and chose ISO 400. Exposures varied from f/4 to f/9 and 1/160 to 1/40 second. The first six images were taken at 1 minute intervals. The last two images were at 5 minute intervals, with the Sun dropping farther below the horizon and the display less interesting.

The “speed” with which a sunset happens is a bit subjective, and while distracted by the display it’s easy to miss this higher-order phenomenon. The Sun itself sets in an easily calculated amount of time. But the duration of sunset colors is a function of the geographic extent of cloud cover. As we learned in my Feb 26, 2018 post, reddish light from the Sun can be abruptly switched on or off by intervening clouds.

I’d never claim that Arizona has the best sunsets on the planet, and I’d certainly never claim that Arizona has the best sunsets on any planet, but I know what I like. Wherever you reside, I urge you to spend some time outside at sunset and see what Nature throws your way. Send me photos if you catch a good one.

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