Hi Kevin, Thanks for your comments and detailed analysis of the numbers calculated - I appreciate it. I am a software engineer by profession and I am routinely asked to implement scientific and technical algorithms. I am just familiarizing myself with solar calculations -though I have implemented them as per available information, it in no way makes me an expert - I am just learning. My interest in this is from the angle of applying it to the solar energy field.
I am using the method as described in NOAA page: http://www.srrb.noaa.gov/highlights/sunrise/azel.html Here are my responses: (1) I don't know about this one - I am just listing the RA as calculated - how did you figure out it was in degrees? (2) Internally the times are in Local Standard Time. (3) Yes, Logitude as entered in the user interface is +ve in East, but internally it is converted to other way around. Yes, you are right - I am based in San Francisco Bay Area! Thank you, Kaarigar =================== ________________________________ From: Kevin Karney <[email protected]> To: [email protected] Cc: Sundials List <[email protected]> Sent: Thu, February 3, 2011 2:37:07 AM Subject: Re: Solar Position Calculator Hi Kaarigar Firstly WELL done. Your web interface is very nice. I think it's great when people get back to basics and understand the background physics/astronomy behind their gnomonics. I remember the satisfaction that came when I first worked things out and found I could generate results of surprising accuracy. To calibrate your routines you should use NASA's JPL's Horizons program or US Naval Observatory MICA - which others have mentioned. The Horizons web application is superb inasmuch as it is easy-to-use, free, fast and can deliver results in spreadsheet format back to your computer. It is continuously updated for the earth's erratic slowing and its internal DE405 routines for the positions of solar system bodies are used by MICA as well - so represents the best available technology. The Horizons printable user guide (which you do not need) contains the wonderful exhortation "if your career or spacecraft depends on a non-lunar satellite or small body ephemeris, contact JPL before using it...". The most sophisticated do-it-yourself astronomical routines available are to be found in Meeus' book "Astronomical Algorithms" which is (I think) out of print, expensive but usually available on abebooks.com. (Does anyone know of a book that betters Meeus ???) What is of interest to gnomonists are simple routines that give sufficient accuracy for sundials. I made a tiny check on your results for today at 8 & 20 hrs UTC = midnight & midday California time using MICA. RA was correct to 11 secs of arc Declination was correct to 3 secs of arc Altitude was correct to 21 & 87 secs of arc Azimuth was correct to 82 & 39 secs of arc The variable error in altitude & azimuth may be because you just calculated a geocentric RA & Decl, whereas to be entirely thorough one should calculate the topographic RA & Decl. But, on that tiny sample, your routines are MORE than good enough for any gnomonic studies ! A few small points to clarify on your web interface... 1) Right Ascension has no units, you have put it in degrees - but it is frequently quoted in hours ? Also, by convention, it is always rectified to within 0 - 24 hours or 0 - 360 degrees. (In contrast, Hour angles by convention are always rectified to -180 to +180 degrees). 2) Are your times in local mean time, local standard time or UTC? Your results seem to be in local standard time - which is logical ! 3) The sign used for your longitude conforms to IAU convention, but many gnomonists seem to prefer +ve West I was interested to know where you came from - so assumed your web interface default location was your home. You appear to live at sea, in the San Francisco Bay!! What is the background of your calculations ? Best regards Kevin Karney Freedom Cottage, Llandogo, Monmouth NP25 4TP, Wales, UK 51° 44' N 2° 41' W Zone 0 + 44 1594 530 595 On 2 Feb 2011, at 20:22, [email protected] wrote: I had asked a question earlier about how to design a contraption such that a sunlight beam falls on a place (or point) exactly each year at a specific time. Having gone through the responses and realizing that I will have to learn to do some basic solar position calculations myself, I have implemented it and made it available through a web site - please check it out and let me know if it is right/wrong/ or simply works. Thanks! > >http://www.heliometry.com/solpos > >Kaarigar >================ >--------------------------------------------------- >https://lists.uni-koeln.de/mailman/listinfo/sundial > >
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