July 31, 2010
I live not far from Chicago's O'Hare Airport, one of the busiest airports in the world. Commercial aircraft not only take off and land at O'Hare but pass high above on their way elsewhere. As shown here, photographed from my backyard, three condensation trails (contrails) are fortuitously aligned. Such attention-getting patterns have been observed more frequently in recent decades as our skies have become increasingly crowded. It’s estimated that conditions supporting contrail formation, which typically occur 20,000 ft (6,096 m) or more above the surface, exist perhaps 10 to 20 percent of the time when the air is clear. The fact that these contrails have spread out and not dissipated twenty minutes or more after forming indicates that sufficient water vapor is present at the level of the jet aircraft to keep the trails intact. When atmospheric moisture is low, the contrails will quickly evaporate. Photo taken on July 18, 2010.
Photo details: Camera Maker: Samsung Techwin; Focal Length: 17.4mm (35mm equivalent: 106mm); Aperture: f/12.4; Exposure Time: 0.0056 s (1/180); ISO equiv: 80; Exposure Bias: none; Metering Mode: Matrix; Exposure: program (Auto); White Balance: Auto; Flash Fired: No; Color Space: sRGB