Seen here on June 13th from southern New Mexico, this Comet McNaught's long ion tail sweeps across the telescopic field of view (a negative image is inset).

这是6月13日新墨西哥南部所见，麦克·诺特的长离子尾扫过望远镜的视野，插图是负片。

youdao

The conventional tail must be at a negative Angle of attack, and the canard tail at a positive Angle.

通常的尾翼必须处于负迎角，而鸭式尾翼则为正迎角。

youdao

Second, the definition ignores tail risk, or the risk of extreme outcomes, including negative outcomes.

FORBES: A Frame of Reference: Downside Risk