Last summer, as I was walking across campus I noticed the above cloud with wave-like structure. This cloud is most likely an isolated example of altocumulus undulatus, which most commonly occurs in the altitude range of 2.5–6 km. This cloud was at approximately a 45-degree elevation, and the wavelength (or crest-to-crest distance) was about the width of my index finger held at arm’s length. Estimate this wavelength.

Estimate the area of the shadow cast on the ground by the cloud. (Assume the cloud lies in a horizontal plane and is of negligible vertical extent.)

Look for the answers online at under “Browse,” at the very end of the current issue.

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