The Celestial Ancient is an immense winged creature that looks like it's made of the night itself. It's darker than the night (or dusk) sky behind it, and its body contains many stars of varying brightness. Wherever the creature's shadow strikes, it is night. It is one of the abstract elemental beings.
"We thought the clouds had moved from the night sky. Then the night sky moved, and the horizon grew wings." -Josuri