< p >没什么令人费解的照片。它有一些不常见的特性,但没有什么未知的。在下图中,我彻底扭曲了亮度曲线使事情更加明显:< / p > < p > < a href = " https://i.stack.imgur.com/pZ7Ty.jpg " rel = " noreferrer " > < img src = " https://i.stack.imgur.com/pZ7Ty.jpg " alt = "在这里输入图像描述" > < / > < / p > < ol > <李> < a href = " https://www.atoptics.co.uk/rainbows/primary.htm " rel = " noreferrer " > < / >主弧。这是典型的“内部反射”彩虹,你在学校学习。李李< / > < > < a href = " https://www.atoptics.co.uk/rainbows/sec.htm " rel = " noreferrer " >二次电弧< / >。当光这一形式反映两次在一个雨滴,扩大弓和扭转颜色的顺序。李李< / > < > < a href = " https://www.atoptics.co.uk/rainbows/supform.htm " rel = " noreferrer " >额外弧< / >。这些都是由光的波动性质:光,甚至一个单一的颜色,通过雨滴扩散。弧是干涉图样由广泛的光从许多小雨滴,因为这个传播,它们通常是柔和的颜色,而不是单频的颜色主弧。在雨滴的大小变化越少,尖锐的弧线;这些尤其尖锐。 Supernumerary arcs on the secondary bow. These are rarely seen, because they're even more sensitive to variations in raindrop size than the primary arc's supernumeraries. Possible fifth-order bow. This faint green patch is in the right place to be the green stripe from light reflecting five times as it passes through a raindrop. Fifth-order bows are almost never seen because of how faint they are, and are photographed even less often, so this may just be an image artifact. Primary glow. Only the light passing through the edges of a raindrop forms the rainbow. Most of the light passing through the middle just goes straight through to form the zero-order glow (not pictured), but some reflects back to form a glow in the middle of the rainbow. Alexander's dark band. The light making up the rainbows has to come from somewhere, and this band is where it comes from. Reflected rainbow. This isn't a reflection of the primary arc (rainbows aren't real objects, so they don't have reflections), it's the rainbow you'd see if your position had been reflected across the plane of the water. All of these have been known to science for quite some time. The primary arc was the first one to be explained, by Persian astronomers in the 1200s. Supernumerary arcs were the last one to be explained, by Thomas Young in 1803.
The "third rainbow" the BBC is talking about is probably the first few supernumerary arcs of the primary arc. Supernumerary arcs have the same color ordering as the arc they're attached to, but because the brightness and width of the arcs varies, and because they're usually pastel colors rather than spectral colors, it can give the appearance of a reversed spectrum.
The "third rainbow" isn't a twinned rainbow, because the second arc of a twinned rainbow (caused by two rainstorms at different distances with different raindrop characteristics) wouldn't be concentric with the first arc.