As I write this post, it’s completely dark outside and it’s only 5 o’clock in the afternoon. Today is 4 December, and most people I come across think that it will continue to get dark earlier and earlier in the afternoons until 21 December, the shortest day of the year (at least for those of us in the northern hemisphere). This, however, is not the case.  The evenings in fact start to draw out a week or so before December 21, although it does not start to get lighter in the  mornings until  early in the new year.

This post aims to explain this interesting phenomenon.

Sunrise and Sunset in December

The table below shows the sunrise and sunset times for London in December 2014.

In the table the daylight interval column shows the number of hours, minutes and seconds between sunrise and sunset. This clearly shows that December 21 has the shortest period of daylight. However, the…