At 10:48 AM 8/12/01 EDT, Bill Gottesman wrote:
>Hello All,
>I know Fred must be right about the declination being non-zero at the
>equinoxes, but I can't figure out why. As I understand, solar celestial
>right ascension must equal solar ecliptic longitude (Lambda) on the equinoxes
>(0 degrees spring and 180 degrees fall).
Bill,
The Sun's ecliptic latitude can amount to a full arcsecond (although
it is usually much less), and this can also cause the Sun's declination
to be slightly different from zero at an equinox. The main reason
is the pull of the Moon, whose orbit is inclined to the ecliptic.
The Earth's center is not precisely at the Earth-Moon barycenter,
but is "orbiting around" the barycenter. This also explains why the
dates of the Earth's aphelion and perihelion dates jump around by
several days from year to year.
-- Roger
