On Tue, 11 Feb 2003, Roger Bailey wrote:
In any case a tropical analemmatic dial suffers from reversing shadows and a
compressed hour ellipse. The question remains. Have any tropical analemmatic
sundials been built?
It would be interesting to draw lines from the terminator maps to the
Hi John and all,
Thanks for your appreciation!
I noticed that the date divisions are at ten day intervals so that the
correction numbers don't look crowded. If one week divisions were used,
the
dateline might get pretty busy.
For the same reason some 10-day markers are omitted towards the
An analemmatic dial at the equator is the simplest case of Samuel Foster's
Diametral Sundial - which I covered in an article in both BSS Bulletin and
NASS Compendium. Foster's idea was published in 1654 - and a facsimile
edition of his original work is in planning for publication later this year
John's point on analemmatic sundials for the tropics is a good one. Look at
how close the date line comes the hour point ellipse at the latitude of 25
degrees, 31 minutes. At the tropic latitude , 23.5 degrees they intersect.
The length of the noon shadow on the solstice is zero as the sun is
