These two applets plot the changes in insolation values and orbital parameters of the earth with time.
The values are calculated following Berger, A. L. 1978 Long-Term variations of Daily Insolation and Quaternary Climatic Changes. Journal of the Atmospheric Sciences, vol. 35, pp. 2362-2367.
There is plenty of information on the topic at: The World Data Center A- Paleoclimatology, which publishes insolation values for the last 5 million years.
At this moment the code does not check for absurd values, so check your inputs. It only works properly for latitudes where the sun rises and set. I will consider an extension soon. Recommended resolution of the screen: 1024 x 768 or higher.
An Excel worksheet with the equations can be downloaded here.
OrbitTerms.java has the core routines in java for the calculation of the orbital parameters.
Solarcalc is a insolation calculator for direct and difusse radiation at any given latitude and terrain orientation.
Comments are welcome