taru-adjective, adverb taking the 'to' particle
bright and brilliant; shining brightly
Literary taru-adjective describing a radiant, brilliant light. Often used in classical or poetic contexts. In modern Japanese, こうろう is rare and mostly encountered in literary or formal writing.
晃朗たる朝日が山々を照らした。
The bright and brilliant morning sun illuminated the mountains.
星がこうろうと輝く夜空。
A night sky where stars shine brightly.