English Translation
The sky was bright and clear.
晴れる = become sunny; 明るい = be bright
There is no translation of “clear” in the Japanese sentence. And 晴れる and 明るい are somehow overlapping. My alternative translation is:
空は晴れて澄みきっていた。（はれてすみきっていた）
晴れ渡った空だった。（はれわたったそらだった）
澄み渡る（すみわたる）is also interchangeable with 澄みきる in this context. Both phrases are frequently used to describe clear sky/air or pure water of a river/pond/lake. 澄み渡る is often used for large/vast space (e.g. sky) because 渡る has the nuance of “throughout” or “across”.
晴れる merely means “become sunny” whereas 晴れ渡る has the nuance of “sunny and clear/fresh with no dust or cloud”.