Why doesn't the solstice coincide with the earliest dawn?

25 January 2011


Using the Southern Hemisphere as example, on or about 22 December (Summer Solstice), the Sun is overhead at its furthest point South (Tropic of Capricorn), causing the longest hours of daylight, for all places South of that Tropic, (and of course, the shortest for all places North). The situation is reversed on or about 21 June (the Winter Solstice).

This being the case, it would be logical to expect that, on the longest day, Sunrise would occur at its earliest for any day of the year, and Sunset at its latest. However, on studying tables of Sunrise and Sunset times, it is clear that this is not the case... The facts are that the earliest Sunrise occurs roughly 3 weeks before the Solstice (1 December), and thereafter starts to occur later again each day. Similarly, the latest Sunset occurs roughly 3 weeks after the Solstice (15 January), and only thereafter starts to occur earlier again each day.

A clear, reasoned explanation for this unexpected phenomenon is needed.

We look forward eagerly to hearing what you think. Cheers and Happy Holidays (if you're a southerner stay cool & if you happen to be in the northern climes, try to keep warm ;-)


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