Nutation
To calculate positions in coordinates referred to the true equinox of date, which takes account of nutation, check the entry Ephemeris -> Nutation from the main menu. If the entry is unchecked coordinates are computed referring to the mean equinox of date. The true equinox of date is available only for geocentric and topocentric ephemeris types; for all other types the mean equinox is used and the selection of equinox is inapplicable. The equinox used is shown in the status bar of the ephemeris window. To toggle between mean and true equinox, click equinox setting in status bar.
It is standard in ephemerides to refer geocentric ecliptical coordinates to the mean equinox of date and equatorial coordinates to the true equinox of date. Topocentric coordinates are not generally tabulated, but using the mean equinox for ecliptical and the true equinox for equatorial and horizontal coordinates, which are computed from equatorial coordinates, would seem to be preferable.
Alcyone Ephemeris
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