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?
The most authoritative solar system ephemeris system is the JPL Horizons system. There is a web interface that will let you perform computations and extract solar system data from the JPL development ephemerides, the international standard.