Thanks Kevin, A quick review demonstrated how useful your work can be for folk like us. Here is a specific example. I have been working with solar and lunar ephemerides date from the JPL Horizons website. http://ssd.jpl.nasa.gov/horizons.cgi#top This site provides a wealth of data that the user can customize for their own purposes. The problem is the user does not know how the data was calculated nor how it is to be used The Explanatory Supplement helps but it is difficult to understand. One simple example is understanding a solar data compilation that provided among other things Right Ascension and Declination. But I really wanted the EQT. Your formula 9 in Part 1 gave me the simple relationship, obvious in hindsight that I was looking for, the conversion of RA to EQT.
I look forward making good use of your work. Thank you for making it available. Thanks again, Roger Bailey Walking Shadow Designs From: Kevin Karney Sent: Sunday, February 23, 2014 11:32 AM To: [email protected] List Subject: Calculating the Equation of Time and other Solar Parameters Dear Friends I have spend many happy hours during this wet, wet winter investigating and learning how to calculate all the solar parameters that a gnomonist might possibly need - Equation of Time, Declination, RA, Altitude, Azimuth, Time of Sunset/Rise, etc, etc. I have been surprised to find that - with traditional calculation methods and an absolute minimum of astronomical information - it is possible to calculate everything from first principles to a surprising degree of accuracy. Other than location and local time, only six pieces of astronomical information are required - obliquity, eccentricity, Sun’s GHA at 1/1/2000, longitude of perihelion, a single precessional constant and the length of the tropical year. Accuracies for the EOT are +/- 2 seconds of time For altitudes/azimuths, less than 1 minute of arc - much better than needed by most gnomonic problems. If any of you are interested in such calculations, I have loaded a document with all the astronomical theory and background plus the code onto my website www.precisedirections.co.uk/sundials The code is written in Python, a language available on every type of computer, which is very easily understood, quite easily learnt and very easily translated into any other coding language you might like. If you own an iPad or iPhone, and are prepared to buy a cheap little app called Pythonista, the code will extract locational & time information from your phone - so you do not even have to input this to get your calculations done You might also like to see a graphic of a civil mean time horizontal dial, which I think is called a hectomoros dial, that is destined for my garden. This is also on the website. Enjoy Kevin -------------------------------------------------------------------------------- --------------------------------------------------- https://lists.uni-koeln.de/mailman/listinfo/sundial -------------------------------------------------------------------------------- No virus found in this message. Checked by AVG - www.avg.com Version: 2014.0.4335 / Virus Database: 3705/7118 - Release Date: 02/23/14 ----- No virus found in this message. Checked by AVG - www.avg.com Version: 2014.0.4335 / Virus Database: 3705/7118 - Release Date: 02/23/14
--------------------------------------------------- https://lists.uni-koeln.de/mailman/listinfo/sundial
