Ghostly flock
Question: I live in the countryside and I have noticed that when walking home
in the twilight the spring blossom on trees—and even a flock of white
sheep—appear almost to glow in the near darkness. Is there something
special about the twilight that produces this effect or is it just me? It is
certainly very beautiful.
Answer: This glowing effect is caused by the re-radiation or fluorescence of
light at longer (visible) wavelengths from scattered ultraviolet, violet and
blue light in the atmosphere. Remember that the daytime sky is blue because of
the preferential scattering of…
