Contrails: Lines the Sky Forgets

A sky is built out of curves and smudges, and then something draws a line through it. The line is exhaust turned to ice: water that left an engine warm and found air cold enough to freeze it in place. It only happens where the air is cold and damp enough to keep it, which is why some afternoons are laced with them and others hold nothing at all.

The interesting part is how quickly they stop being straight. A fresh one has a hard edge and a bright core, drawn maybe two minutes ago. An hour later the same line has gone soft and wide, bent by winds that were invisible until the sky had something to bend, and by evening it is indistinguishable from ordinary cirrus. The plane has landed somewhere; the sentence it wrote is still being blurred.

At dusk they are the last things lit. The ground has gone blue, the clouds have cooled, and a trail eight kilometres up still catches a sun that set here twenty minutes ago. On a screen that kind of picture is easy to live with — an empty sky with one line across it gives the eye a direction to take and nothing else to do.