(50g) Week day / Season begin / Mean / True ecliptic / Julian Day / Astron Nutation

[Gil]

The calculation for the tropical year was added recently to the directory.

An error relative to it was fixed up in this
new version Xi (the reference of which + date to be found on last page 10.5 of the directory).

The input and output for the tropical year (at page 1.5) are now saved on page 2.1 & 2.2 under names DAT.T (for Date T=Tropical) & TRP. YR.

On page 2.3, the input for the epsilon program (at page 1.6), is now labelled DAT.epsilon (and no more under name DATE.H).

As always, possible to find the Julian Day from (page 1.4) starting from "calendar date + fraction of day" and reverse (page 1.3).

Season and weekday calculation remain at the very beginning of the directory, at pages 1.1 & 1.2.

My thanks to Pascal Descamps of Institut de mécanique céleste et de calcul des éphémérides (IMCCE) for his readiness in forwarding me the formulae relative to tropical year, including its most up-to-date expression in connection with VSOP2013.