Re:

[Fer J. de Vries]

Hi Noam,   Of course the refraction effects the hourangle of all the time systems we use in dialling. But also keep in mind the historical meanings of used systems as the temporal hours.   Temporal hours are calculated in respect to the center of the sun as we do for other time systems. The times of sunrise and sunset however are calculated for the limb of the sun. Should we care about that either?   We want to have time in seconds and even in smaller parts. But in older days the feelings about time was much different. Temporal hours were used as a period of time peolple was in, not an exact moment of time as we often use.   Calculating the temporal hour lines shows that the lines aren't straight but sligthly S-shaped which is best visible with increasing latitude but in older dials the lines are drawn as straight lines.   It's good to think about the effect of refraction but in general I should say, forget the refraction in dialling.   Best wishes, Fer.     Fer J. de Vries   De Zonnewijzerkring mailto:[EMAIL PROTECTED] http://www.de-zonnewijzerkring.nl   Home mailto:[EMAIL PROTECTED] http://www.iae.nl/users/ferdv/index-fer.htm Eindhoven, Netherlands lat.  51:30 N      long.  5:30 E ----- Original Message ----- From: Noam Kaplan To: sundial@rrz.uni-koeln.de Sent: Friday, September 24, 2004 12:30 AM Can anyone answer this? If this is the wrong forum, I apologize. I have a calculation to figure out the atmospheric refraction from Fred Sawyer's article in the NASS Compendium. It is based on calculations that Meeus brings in his book. Refraction changes the apparent altitude of the sun, thereby changing both the apparent declination and apparent hour angle of the sun.   Am I making a mistake when I use the apparent declination and apparent hour angle for the temporal hour calculation? The effect of a few seconds difference for atmospheric refraction on the hour angle seems to have a much bigger effect on the temporal hours.   Thanks for any help you can offer, Noam   My calculations can be seen on the web at http://www.riets.edu/stuff/suncalc/zman.js in the function temporal(localTime)