What is a lunar rainbow and why is it white?
A16: Like the sun, the moon can also generate rainbows. However, because moonlight is much less intense than sunlight, the lunar rainbow usually is too dim for us to see any colors in it. Recall that even under a full moon, objects that look vividly colored during the day appear only in shades of gray. Thus the lunar rainbow is white (Chapter 8; Minnaert 1993, pp. 207-208). Q17: What are the pale green and purple arcs sometimes seen within the primary rainbow? A17: These are the supernumerary rainbows. Despite their superfluous-sounding name, they are an integral part of the rainbow (Figs. 8-3, 8-8). In fact, explaining how supernumeraries occur also explains the primary and secondary rainbows (see A14 above). Q18: Why does a rainbow grow brighter and darker so quickly? A18: See A6 above. Q19: Can I touch the rainbow or reach its end? A19: No. Because the rainbow is an image, not an object, you can never reach or touch it (Chapter 4). However, in the same way that you can touch a mirro
