A clear sky is a sky with no cloud in it at all. Under a clear sky, a clear sky tonight, wait for a clear sky.
A clear sky at night means a cold morning, since nothing holds the day's heat in. It is what astronomers wait for and what gardeners fear in spring, when frost follows.
1nounclear skyA sky with no cloud in it at all.
“They set the telescope up under a clear sky at last.”
clear sky is a sky.
Practised in Weather & Seasons