Like anything that is not completely see-through, the water vapor from jet planes, called jet contrails (NOT chemtrails), can cast shadows. These can create some interesting photo opportunities, and we show a few here, submitted by EarthSky readers. As well, even though shadow casting is normally nothing strange, the appearance of contrail shadows can at times make us scratch our heads: are they actually above the contrail or below?
We wondered what light source was creating the shadow and asked an expert, Les Cowley at the great website Atmospheric Optics. On his page about jet contrails, you can read what he said:
Contrail shadows sometimes appear counter-intuitive. [They may seem to be cast] by a low altitude bright light shining upwards and casting the contrail shadow on a higher cloud. The reverse is the case …
In other words, he said, the jet itself and its contrail are always higher up than the shadow, which is cast on clouds below. By email, Les told us:
Contrail shadows often don’t look ‘right’ and seem as if the contrail is below the clouds. But the shadow casters – the sun and moon – always shine downwards so the shadow must be below the contrail.
Like all statements there is an exception! At sunset and sunrise rays can travel very slightly upwards to illuminate the underside of clouds. Under those circumstances however a contrail shadow would be a long way from the contrail.
And that might be the case for some of the photos showcased here. You will need to check the time the photograph was taken and the distance of the shadow to try to discern whether the shadow is below (which is normally the case) or maybe actually above the contrail!
Bottom line: Shadows from jet contrails often appear to be above the contrail, seemingly cast by a low-altitude bright light shining upwards. In fact, the shadow is normally cast on clouds below the jet and its contrail since the sun (and the moon) are above. View images submitted by EarthSky readers here.