Name something you can see in the sky (no living or manmade things)
STEVE
STEVE is a natural purple auroral sky phenomenon named from the film Over the Hedge.
Airglow
Airglow is a faint emission of light by Earth's atmosphere, a natural night-sky phenomenon visible from the ground.
Source:en.wikipedia.org
Brocken spectre
A Brocken spectre is the magnified shadow of an observer cast on clouds, an optical phenomenon seen in the sky.
Source:en.wikipedia.org