---------- Forwarded message --------- From: Michael Ossipoff <email9648...@gmail.com> Date: Fri, Oct 14, 2022 at 10:16 PM Subject: Re: How to turn ecliptic longitude into solar declination? To: Steve Lelievre <steve.lelievre.can...@gmail.com>
Or you could just use the ecliptic longitude, reckoned as usual from the Vernal Equinox…multiply its sine by the sine of the obliquely & take the inverse sine of the result. I’d suggested that other way because there are some spherical trigonometry formulas that require an argument between 0 & 90 degrees. …but that isn’t one of them. > > > On Fri, Oct 14, 2022 at 6:49 PM Michael Ossipoff <email9648...@gmail.com> > wrote: > >> Multiply the sine of ecliptic longitude (reckoned forward or backwards >> from the nearest equinox) by the sine of 23.438 or whatever the current >> obliquity’s exact value is). >> >> Take the inverse sine of the result. >> >> On Fri, Oct 14, 2022 at 4:57 PM Steve Lelievre < >> steve.lelievre.can...@gmail.com> wrote: >> >>> > Of course you’ll know when the declination is negative or positive, so > mark it accordingly. > > > > Hi, >>> >>> For a little project I did today, I needed the day's solar declination >>> for the start, one third gone, and two-thirds gone, of each zodiacal >>> month (i.e. approximately the 1st, 11th and 21st days of the zodiacal >>> months). >>> >>> I treated each of the required dates as a multiple of 10 degrees of >>> ecliptic longitude, took the sine and multiplied it by 23.44 (for >>> solstitial solar declination). At first glance, the calculation seems to >>> have produced results that are adequate for my purposes, but I've got a >>> suspicion that it's not quite right (because Earth's orbit is an >>> ellipse, velocity varies, etc.) >>> >>> My questions: How good or bad was my approximation? Is there a better >>> approximation/empirical formula, short of doing a complex calculation? >>> >>> Cheers, >>> >>> Steve >>> >>> >>> >>> >>> >>> --------------------------------------------------- >>> https://lists.uni-koeln.de/mailman/listinfo/sundial >>> >>>
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