【英语时差8,16】蓝鸟为什不蓝？（下）（在线收听）

 The glittery blues seen on bird wings are often caused not by pigment, but by the way light waves interact with the feather. Physicists call this “structural color”. Because of the layered structure of the feather, light waves entering it bounce back at different times and thus collide, or “interfere” with each other. Certain wavelengths get cancelled out while others become reinforced. The reinforced colors that come back strongly to your eye are mostly in the blue range. The result is that eye-catching display of blues. As it turns out, there aren’t many blue pigments used by birds in general. So any time you see blue or purple on a bird’s wing, you can suspect that at least some of it is structural color. Especially if it’s got that razzle-dazzle effect.