This module computes solar insolation at any latitude and any time from 250 Ma to the Recent (the results are less accurate before 50 Ma). The calculation can be done for a "true" orbital longitude, "mean" orbital longitude (corresponding to a certain date in the year), averaged over a certain month in each year, or integrated over a whole year.
The implementation in PAST is ported from the code by Laskar et al. (2004), by courtesy of these authors. Please reference Laskar et al. (2004) in any publications.
It is necessary to specify a data file containing orbital parameters. Download the file INSOLN.LA2004.BTL.250.ASC from http://vo.imcce.fr/insola/earth/online/earth/earth.html and put in anywhere on your computer. The first time you run the calculation, PAST will ask for the position of the file.
The amount of data can become excessive for long time spans and short step sizes!
Reference
Laskar, J., P. Robutel, F. Joutel, M. Gastineau, A.C.M. Correia & B. Levrard. 2004. A long-term numerical solution for the insolation quantities of the Earth. Astronomy & Astrophysics 428:261-285.