This is the 3211th most frequent Russian word.
небе
"Небе" is the dative or prepositional case of "небо," meaning "sky" or "heaven" in English.
'небе' refers to the sky as part of the idiomatic expression 'На небе' meaning 'In the sky'.
На небе светит яркое солнце.
A bright sun shines in the sky.
Here, 'небе' is in its locative form, denoting the location, 'sky', during the evening.
Я увидел облака на вечернем небе.
I saw clouds in the evening sky.
In this sentence, 'небе' is used to indicate the place where the birds are flying, emphasizing the spatial attribute.