Noam Kaplan queried: > ... why does Waugh write that the sun will never shine on > a vertical direct south dial before 6 AM or after 6 PM?
Hmmm. The erudite answer from Tony Moss notwithstanding, this assertion, as written, is not strictly true. With his recent travels to the Far North fresh in his mind, Tony will know that once you cross the Arctic Circle all kinds of rules start to go awry. Let us start with Tony's example: ...on midsummer day the sun rises at my latitude - 55° north - at just after 3.0am (GMT) and at a point on the horizon approx. 45° north of due east. Before/after 6.0 am/pm it is shining on the north face of an east/west wall. This is correct. The sun shines on the south side of the wall for only about 9 of the 18 hours that it is above the horizon. As you go further north, the time the sun shines on the south side of a direct south-facing wall gradually increases until, when you reach the arctic circle, it shines on the south side for about 11 hours. The tantalising bit comes next... On the day of the summer solstice the sun is above the horizon for all 24 hours at the arctic circle so it is on the NORTH side for about 13 hours. This still doesn't violate Waugh's assertion but... Translate your wall to the ANTarctic circle and here, at OUR winter solstice, the sun shines on the SOUTH side for about 13 hours. These are the hours from roughly 5:30pm to 6:30am which include ALL the hours between 6pm and 6am that Waugh is denying us. All we need now is a client for Tony Moss who wants a wall dial in the Antarctic and we can see this at work. Frank King Cambridge University England -
