Maybe it's because the skies are more colorful, but it seems like there are quite a few airplanes flying over our heads these days. They are very easy to see thanks to the vapor trails that they leave behind in the sky.

Vapor trails, or contrails as some people call them, are man-made clouds that sometimes form behind aircraft. Their formation is triggered by the water vapor emitted in the exhaust of aircraft engines, but can also be triggered by the changes in air pressure in the air over the entire wing surface of the plane.

So why is it you can see them for long periods of time and other times just for a few seconds? The length of viewing is determined by the temperature and humidity at the altitude that the contrails form. Persistent spreading contrails are thought by some, without overwhelming scientific proof, to have a significant effect on global climate.

And now you know.  I enjoy watching them form as the aircraft flies overhead. It's also fun to guess just where that plane might be headed.