冴(さ)えるto be clear (of a sight, sound, colour, etc.), to be bright, to be vivid, to be crisp, to be clear-headed, to be alert, to be on the ball, to be wide awake, to look upbeat, to be perky, to be cheerful, to master (a skill), to excel at, to cleanly execute, to be satisfying, to become frigid, to become intensely cold

田舎(いなか)の夜空(よぞら)では星(ほし)が冴(さ)えています。

In the countryside night sky, the stars are shining brightly.

プロのバイオリンの音色(ねいろ)は冴(さ)えている。

The tone of a professional violin is vivid.

冬(ふゆ)の夜(よる)は冴(さ)えるので、温(あたた)かくして寝(ね)て下(くだ)さい。

The winter nights are frigid, so please sleep warmly.

私(わたし)は冴(さ)えた赤色(あかいろ)の薔薇(ばら)に加(くわ)えて、淡(あわ)い赤色(あかいろ)の薔薇(ばら)も大好(だいす)きです。

In addition to bright red roses, I also love pale red roses.

精神(せいしん)科(か)医(い)：「気分(きぶん)が冴(さ)えない時(とき)はランニングか何(なに)かで体(からだ)を動(うご)かすといいですよ。」

Psychiatrist: 'When you're not feeling perky, it's good to get moving, like going for a run or something.'