This is the 18502nd most frequent Russian word.
ясного
"Ясного" means "clear" or "bright" in English, depending on context.
The word 'ясного' is used as an adjective modifying 'утра', describing the clarity characteristic of the morning.
В ясного утра воздух свеж и чист.
On a clear morning, the air is fresh and clean.
Here 'ясного' describes 'лунного диска', indicating the moon's clarity in its appearance.
Свет ясного лунного диска озарял улицы.
The light of the clear moon disk illumined the streets.
In this context, 'ясного' describes the state of understanding, indicating clarity or lack of confusion.