Hello Frank ,
In my opinion the Waugh's statement is correct if we think only to the
sundials in the North hemisphere (as Waugh did).
For a sundial in the South hemisphere, with latitude smaller then - 24°, the
"active" face (the one mostly exposed to the Sun) is the North face and
therefore for the South hemisphere the sentence of Waugh should have changed
in "the sun will never shine on a vertical direct North dial before 6 AM or
after 6 PM"
For this reason it seems to me a little " trick " to consider the period of
illumination of the South face in a sundial to the ANTarctic polar circle
:-)
For curiosity I send some approximate values (calculated with mean values of
the Sun's declination) for the day June 20th
Latitude
55°
66° 27'
89°
90°
Dawn
3h 27m
0h 00m
0h 00m
0h 00m
Start of the illumination
7h 11m
6h 43m
6h 02m
6h 00m
Sun's altitude
29.1°
25.7°
23.45°
23.45°
Length of the illumination
9h 39m
10h 33m
11h 56m
12h
Length of the day
17 06m
24h 00m
24h 00m
24h
Gianni Ferrari
44° 39' N 10° 55' E
Mailto : [EMAIL PROTECTED]
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