Fun With Contrails … And Auroras

“X” marks the (sun) spot! Contrails from two planes formed the letter X. The sun followed along the one “spoke” as winds pushed the contrails east. Cool! Bob King

Contrails, those streaks of condensed moisture that form in the wake of high-flying aircraft, can be annoying if you’re a photographer. They mark up an otherwise blue sky and can add an unwanted man-made element to pristine landscape photos. But sometimes contrails can become a subject of their own, where they add an geometric or atmospheric flavor to a scene.

Three separate feathery contrails bisect a lunar halo last month. You can also see the shadow that each contrail casts on a lower layer of clouds. Bob King

Contrails — short for condensation trails — are clouds that form behind a plane when water condenses on tiny soot-like exhaust particles produced by the burning jet fuel. They’re not smoke from the engine, but made of water ice. Most of the water comes from the surrounding air with a smaller part from the plane’s engines. They form at high altitudes where the air is extremely cold, usually less than -40° F (-40° C). Depending on humidity and wind direction at airplane altitudes, contrails can disappear quickly or linger and spread into a band of thin clouds.

People have been watching contrails since the early days of aviation, with the first contrail reported in 1918. They’re common now since so many of us live under or within sight of a flyway. Keep your mobile phone at the ready because you never know when you’ll see interesting patterns created by these airplane-induced ice crystals.

Last night, the northern lights put on a gentle show in the lower half of the northern sky. Bob King

The northern lights arrived on schedule last night. I noticed a glow low in the northern sky around 10:45 and got out at 11:30 with a camera. What a wonderful time: watching the display, standing in an open field with spring peepers for background sound. There are things to love about spring. I saw faint rays reaching to about 35, a few moving rays (from east to west) and some palpitating glows closer to the northern horizon.

There’s a chance for more minor aurora tonight early on around nightfall for the northern parts of the northern states.

Jupiter rises over a wavy Lake Superior in Duluth during twilight last night (May 6). Bob King