Peter Ross captured this strange sight.
The sun was low, behind and to the right of the aircraft. The antisolar point, directly opposite the sun, is at image centre and 30-45° left of the plane's heading.
Upwards from the antisolar point are familiar anticrepuscular (antisolar) rays. Why do we call shadows, rays? Clouds cast these shadows. Clouds higher than the aircraft but otherwise anywhere in the sky. One ray from a lower altitude cloud streams inwards from the right. The rays are all parallel. They only appear to converge with distance.
The dark and curved shapes are more puzzling. They are shadows. From what? And why curved?
The aircraft is making contrails. Their shadows project through the sky ahead of the plane and to its left because the sun is shining from the right. On the flight deck they stream from the left towards the antisolar point.
Why curved? On many aircraft the airflow and engine nacelle angle induce contrails to initially curve downwards before levelling out. This helps give the peculiar shadow shapes, especially to the right-hand one coming in from below the airplane.
Photographs ©Peter Ross, shown with permission