How to determine the limits of the extreme period?


First of all, one must calculate the astronomical phenomena (i.e. twilight rise, sunrise, noon, sunset, twilight set and midnight) times for the whole year. Visually the astronomical phenomena times may be plot in a figure.

In order to determine if there is any summer extreme period and its corresponding limits, the following checks focusing on summer (or even could start from late spring to early autumn) can be done:

The limit which gives the longest period of summer extreme period is selected.

In order to determine if there is any winter extreme period and its corresponding limits, the following checks focusing on winter (or even could start from late autumn to early spring) can be done:

The limit which gives the longest period of winter extreme period is selected.