September 08, 2003
Even though at first glance the photo above is breathtaking, it's also a bit disturbing. Those myriad crimson streaks slicing the purple sky result from jet condensation trails (known as contrails), which here are being highlighted by a sunken Sun. This photo was captured last September over the Netherlands, shortly after sunset. Contrails form when hot jet exhaust mixes with the extremely cold (less than about -25 F or -32 C) ambient air of the upper troposphere (greater than about 25,000 ft or 8,065 m). When contrails cross the sky, the atmosphere, at the level of the jet aircraft, has to be near saturation. Contrails are especially noticeable where commercial airlines have established flight paths, for example, from northern Europe to the northeastern U.S.
Today marks the beginning of the 4th year of the Earth Science Picture of the Day.