Check out this amazing picture taken last Monday during the solar eclipse (seen as a partial eclipse from Montreal).
Chloe Rose Stuart-Ulin explains in the New York Times:
The plane passing over Montreal during the partial phase of the eclipse left a typical contrail in its wake. When this happens in full sunlight, the shadows cast by contrails on clouds are usually too diffuse to see. In this case, the sharpness of the shadows was explained by the eclipse.
Though the shadows of the contrails appeared to be on a layer of clouds above the aircraft, as though cast from reflected light from the Earth, this was an illusion. The shadows were made by the light of the sun, cast downward onto clouds below it.
