The sun has set from the POV of the camera, but not from the POV of the contrail which is both miles west toward the sun, but more importantly probably ~30,000 feet higher than the camera. So you see the sun light reflecting off the bottom of the contrail.
The sun has set from the POV of the camera, but not from the POV of the contrail which is both miles west toward the sun, but more importantly probably ~30,000 feet higher than the camera. So you see the sun light reflecting off the bottom of the contrail.In that case then the furthest west point of the contrail would be the last part to fall into shadow.
As you can see there the "farthest west," or bottom, of the contrail is the first to fall into shadow. It also passes in front of a line of clouds in the distance. If it were an airplane at 30k ft coming from the horizon it would pass over that relatively near and low line of clouds.