[fitswcs] Draft WCS Paper V: Time

[Patrick Wallace]

William Thompson wrote:

> However, I'm not entirely certain how one distinguishes between the
> mean ecliptic of date and the true ecliptic of date in Calabretta
> and Greisen.

There is no such thing as mean ecliptic of date, nor true ecliptic of
date are incorrect terms.  The ecliptic by definition is a secularly
moving plane.  There are only two sorts:  J2000, which is fixed in
ICRS, and "of date", which slowly turns as the Earth's orbit is
disturbed by the planets.


Patrick Wallace
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