Secondary Rainbow

Secondary rainbow and reversed colours Primary and secondary rainbow

A bright primary bow with a much fainter secondary bow showing the reversed colours. The primary bows comes from light reflected once inside the drops while the secondary comes from light reflected twice.

The secondary is much fainter than the primary so it is usually only seen when there is a strong primary and a suitable background. Only a fraction of the light entering a raindrop ends up in the bow anyway.

Strong secondary rainbow Faint secondary rainbow on its own

A strong secondary bow stands out against the dark background Apart from the strong primary and secondary bows this dramatic rainbow showed most of the rainbow features. These included supernumerary bows, the brightening inside the primary bow and, very subtly, the brightening outside the secondary.

At first glance there is nothing to see here, but a faint secondary bow does run diagonally across the image toward bottom right. The sun altitude was 37 degrees so even if there was a primary bow it would barely have reached over the hills to the left. It was only because I was looking out for this bow that I even noticed it.

Other Bows Topics