Solar time angle at midpoint of the period (for periods < 1 day).
w(x, long.deg, control = list(Lz = 345))date-time object (e.g, POSIXct, POSIXlt or Date objects).
longitude of the measurement site (degrees east of Greenwich) (for periods < 1 day)
list for control parameters and empirical factors (see Details)
Allen, R. G., Pereira, L. S., Raes, D., & Smith, M. (1998). Crop evapotranspiration-Guidelines for computing crop water requirements-FAO Irrigation and drainage paper 56. FAO, Rome, 300(9).