明(あか)らむto become luminous at dawn (esp. the sky)

朝(あさ)五(ご)時(とき)になり、東(ひがし)の空(そら)が明(あか)らんできた。

At five in the morning, the eastern sky began to become luminous at dawn.

冬(ふゆ)になると、明(あか)らむ時間(じかん)が遅(おそ)くなります。

In winter, the time when it becomes luminous at dawn becomes later.

今(いま)は真夏(まなつ)なので朝(あさ)に空(そら)が明(あ)らむ時間(じかん)が早(はや)いです。

Since it is midsummer now, the time when the sky becomes luminous at dawn is early.

まだ明（あき）らんでいない時間帯(じかんたい)に運転(うんてん)するのは極(きわ)めて危険(きけん)です。

Driving during the time period when it has not yet become luminous at dawn is extremely dangerous.

季節(きせつ)が冬(ふゆ)へ移(うつ)ったのだから、空(そら)が明(あ)らむのが遅(おそ)くなるのも当然(とうぜん)である。

Since the season has shifted to winter, it is only natural that the sky becomes luminous at dawn later.