When the sun and moon are near the horizon, we notice that they are distorted from a circular form into ovals, and are usually o
f a reddish colour. The former effect is due to the fact that the amount of refraction changes rapidly near the horizon, being greater below than above. Thus the lower edges of these bodies are raised more than the upper ones, so that the vertical diameter is diminished. The horizontal diameter is not affected, and so the sun and moon appear to be oval and not circular. Their reddish colour is due to absorption. White light is composed of all the “colours of the rainbow” —red, yellow, green, blue, violet, etc., —and of these, the green, blue, and violet (the shorter “waves”) are more readily absorbed by the atmosphere, or rather its vapours (for pure dry air exercises scarcely any absorption), than the red and yellowish rays (which are longer). Thus this process of selective absorption results in the loss of a greater amount of the blue and violet rays, and so the sun and moon, when seen low down near the horizon, appear reddish or yellowish rather than white, an effect seen also when the sun shines through a “November fog.” Which of the following most belongs in a set of notes about the passage? “an effect seen also when the sun shines through a ‘November fog.’” “White light is composed of all the ‘colours of the rainbow’—red, yellow, green, blue, violet, etc.” “When the sun and moon are near the horizon” “Thus this process of selective absorption results in the loss of a greater amount of the blue and violet rays, and so the sun and moon, when seen low down near the horizon, appear reddish or yellowish rather than white”
