This article ran in The Textbook Letter for May-June 1992,
accompanying a review of the high-school book PSSC Physics.

In the Land of the Midevening Sun

Lawrence S. Lerner

I was so impressed by the accuracy of PSSC Physics that I spent a while in puzzling over what seemed to be one of the book's few errors. The photograph on page 1 has a caption saying, "A picture of the sun at midnight (Daylight Saving Time) in the Aleutian Islands. The photograph was taken on the Island of Attu at a latitude of 53 degrees." What the photograph shows is a bleak seascape in which the sun, though veiled by clouds, is obviously well above the horizon.

But how can we see the midnight sun at a latitude that is so far below the Arctic Circle? In most other textbooks, the apparent contradiction would not have seemed important: I probably would have dismissed it by assuming that some hack had decorated a page with a picture that bore no connection to reality. PSSC Physics, however, is the work of careful writers, not hacks, so the matter seemed worthy of some inquiry.

Attu is at the southwestern end of the Aleutian chain. When I consulted an atlas I found that, although Attu is politically a part of Alaska, it lies about two and a half time zones west of the Alaska Standard Time meridian (150 degrees W). Hence the sun time on Attu is some 2.5 hours earlier than the sun time at Anchorage, on Alaska's mainland. The clock time on Attu is the same as the clock time on the mainland, but only because time-zone boundaries have been gerrymandered to produce that result.

After subtracting the 2.5-hour discrepancy, I subtracted another hour to allow for Daylight Saving Time. Now I had the answer: Though the clock time on Attu was midnight when the picture was taken, the sun time was only 8:30 PM -- and it is hardly unusual for a summer sun to be above the horizon at that hour. In a way, then, the photo is erroneous (or at least misleading). Maybe the next edition of the PSSC textbook will show us a real midnight sun -- one that can be seen, at Arctic latitudes, when the local sun time is indeed midnight.

Lawrence S. Lerner is a professor in the Department of Physics and Astronomy at California State University, Long Beach. His specialties are condensed-matter physics, the history of science, and science education. He served on the panel that wrote the State of California's 1990 Science Framework, which guides science education in California's public schools.


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