This graph shows the levels of solar radiation recorded daily in
Martinborough, New Zealand between the 1st of Jan. and the 31st of Dec. 2014,
reported against the number of hours of sunshine in that day.
Although a clear linear relation is visible, there is still a high unexplained
variance in the data.
Click on the graph to show the date of recording ... It now appears that the variation
in the relation radiation vs. sunshine hours is related to the season. (Recall that
the New Zealand summer takes place from December to March)