The earth isn’t at night or dark at all altitudes at the same time.
It might be night on the ground but high up it might still be day.
This is exactly what happens at sunset.
Not much is know about this phenomenon also known as polar mesospheric clouds.
The following picture shows such a man made noctilucent cloud.
More information and photos on their site.
Here are two more galleries of noctilucent cloudsNoctilucent Cloud ImagesTunguska
