Article of the month May

Horizontal sundial

Effect of a wide style triangle on date line shape

Below is a horizontal sundial with two time systems:
- local apparent time on the outsidee
- zone time on the inside.    That is, apparent time adjusted for longitude.

Every other hour is numbered.
Pairs of hour lines are joined at the ends, forming islands.

Besides time indications, there are date lines according to the signs of zodiac. They are used with the index: a small horizontal bar on the style triangle, just visible over the equinox.

The sundial has a wide style triangle.

Earlier, this site discussed the effect of a wide style triangle on the hour lines.
The hour lines above the VI - VI line must be moved out; those under it, in.
The blue lines illustrate this.
See Article of the month, 2003 archive, month 03-08.

The wide style triangle has a similar effect on the date lines.
Those parts of date lines that are above the VI - VI hour line must be moved out, together with the hour lines; parts below move inward.
This explains the kink visible in two of the date lines.