七月流火

Etymology
From the , poem 154 (《詩經·豳風·七月》):



In antiquity, Chinese astronomers saw the westerly motion of Antares, the Great Fire Star (大火), as a sign of autumn's arrival. Whether this idiom should be interpreted as referring to the current heat or the imminent cooling is a matter of constant dispute.

Idiom

 * 1) the summer heat recedes during the seventh lunar month, and the cold season becomes imminent
 * 2) scorching heat during July