# Is there an “authoritative” source for ephemeris data?

I find some variation in the values reported for ephemeris by the various sources I have access to. For example for 2012-11-27T03:31:55 UTC I get solar declination values of -21.1828°, -21.18296°, -21.1814°, -21.1834°, -21.1906° and (again) -21.1814°. Are the differences among these values meaningful? Is there an "authoritative" source (ideally online) for ephemeris data?

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Out of curiosity, have you gotten similar inconsistencies with point sources? The Sun might be special. Also, a quick glance tells me several of these sites give $\pm 1$ arcsecond (0.0003 degrees) as the precision. –  Chris White Nov 28 '12 at 2:57

Agreed. That's what started me wondering. I was using Wolfram (Alpha and Mathematica's AstronomicalData) and was getting weird results. Do you know if there is a web-based API that uses their algorithms? Something I can call from code as a substitute for AstronomicalData. (I can check the docs, but if you know off hand that would be great.) –  raxacoricofallapatorius Nov 28 '12 at 1:38
My purpose is just basic study, so I don't need especially precise ephemeris (e.g., I'm not aiming a research telescope). One thing I'm trying to do "rediscover" some basic astronomical patterns and properties (e.g. the equation of time) using the datasets such as Wolfram's AstronomicalData, but I keep running up against small discrepancies that I can't explain, and wonder of they're from inaccuracies in the data. (That matters because the alternative may be instructive, e.g. revealing something like precession or $\Delta T$.) –  raxacoricofallapatorius Nov 28 '12 at 1:44