Dear
Dialists,
I have been
pondering the effect of refraction on dial performance.
Refraction quoted at
.1 degree to .5 degree apparent difference in altitude below 10 degrees of
altitude, will impact the hour angle to some degree. See http://www.gcstudio.com/calcuse.html These
are average values - refraction (according to Meeus quoting someone) can vary by
up to .3 degree at the lower altitudes.
1. It would seem to me that dials
that attempt to tell time during the hour after sunrise and hour
before sunset could usefully take refraction into account. However
altitude for a given hour angle changes through out the year.
Are there dials laid out with reference to average refraction
effects?
And
2. We know that Mean
time + EoT = Apparent Time
However because
viewing the sun through our atmosphere's refraction is unavoidable -
Is there
established terminology to distinguish between Apparent Time (geometric) as
just defined above and Actual Observable Apparent Time (after
refraction)?
David
