Meeus's Astronomical Algorithms is not out of print. Check out http://www.willbell.com/math/mc1.htm. Also, it's cheaper on the publisher's website ($30 + S&H). Brad
On Thu, Feb 3, 2011 at 5:41 AM, Kevin Karney <[email protected]> wrote: > 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 > > > --------------------------------------------------- > https://lists.uni-koeln.de/mailman/listinfo/sundial > > >
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