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Regarding Archie Howitt’s letter in the September 2018 issue, the Sun isn’t normally due south at 12:00 UTC. The ‘equation of time’ resulting from Earth’s elliptical orbit means the Sun crosses the Greenwich meridian more than 16 minutes early in the first week of November and 14 minutes late in the middle of February.
An observer’s longitude should also be taken into account. Edinburgh, where Archie is based, is more than 3° west of the Greenwich Meridian, which means that the Sun will cross the Meridian there some 12 minutes after it crosses the 0° longitude line. Using the Sun’s shadow at 12:00 UTC without accounting for these two together, he could be off the true north/south line by up to 6.5°. Bev Ewen-Smith, Centro de Observação Astronómica no Algarve (COAA), Portugal