Sky at Night Magazine - - INTERACTIV­E -

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

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