Art At the solstices there is no ambiguity. The analemma intersects the tropic of cancer and the tropic of capricorn at one point so there is only one value for the EoT. At all other times of the year, except for one instant when the two paths of the analemma cross, there is only the need to know which leg of the analemma to use. This does not require knowledge of the date, only knowledge of the season. True, the date of the solstices is needed if one is to know if the sun has started north or south yet. In the spring the lower right leg is used (with the analemma viewed projected onto a sphere with the gnomon in front of the analemma, upper left if the analemma is projected onto a surface behind the gnomon), upper left in early summer, upper right in late summer and lower left in the fall. I place a small arrow on each leg of the analemma to indicate the motion of the sun during the year. This identifies to the user which leg to use. One could also label each leg with the season but there does not seem to be reason to know the date.
I have attached two views of the analemma, one as projected onto a sphere and one projected onto a plane behind the gnomon. The first shows the arrows that I use, the second I have labeled with the season. Dan Wenger >Daniel Lee Wenger <[EMAIL PROTECTED]> writes: > >> The reading of standard time via a sundial may be accomplisted by >> mearly reading the declination of the sun and using an analemma, >> determining standard time. At no point is the current date needed to >> do this. > >Way, way back I explained why I was not totally satisfied with this >method, essentially because there are (almost always) two values of >the EoT for each value of declination. At the solstices there are >even an infinite number of values (in some technical sense). >Consequently, if you are interested in relating the sundial reading to >clock time, you always need some knowledge of the current date. > >Art Carlson Attachment converted: Macintosh HD:analemma.arrows.gif (GIFf/GKON) (0000FB7A) Attachment converted: Macintosh HD:analemma.labeled.gif (GIFf/GKON) (0000FB7B) Daniel Lee Wenger Santa Cruz, CA [EMAIL PROTECTED] http://wengersundial.com http://wengersundial.com/wengerfamily
