This function calculates the obliquity for a given epoch. It is a
wrapper for function swe_calc_ut of package swephR.
Usage
obliquity(year = skyscapeR.env$cur.year)
Arguments
year
Year for which to calculate the obliquity.
Defaults to present year as given by Sys.Date
References
Laskar, J. et al. (2004), A long-term numerical
solution for the insolation quantities of the Earth, Astron.
Astroph., 428, 261-285, doi:10.1051/0004-6361:20041335.