This is the 13814th most frequent Russian word.
ночное
"Noчное" means "nighttime" or "night-related" in English.
Here, 'ночное' is used as an adjective describing 'небо' (sky), indicating that the sky is observed during the night.
Я обожаю ночное небо.
I adore the night sky.
In this sentence, 'ночное' is an adjective modifying 'время' (time), highlighting the time of night as the part of the day being referred to.
Ночное время считается самым спокойным.
The nighttime is considered the most peaceful.
This usage of 'ночное' modifies the noun 'чтение' (reading), designating the activity as occurring during the night.