When is the shortest day when days get longer?

Graph of solar parameters

Graph of three solar parameters that affect the time of sunrise and hence the shortest day in the northern hemisphere. Latitude is a fourth parameter.

Summer has come and days are warmer—holidays are round the corner—but longer days are here no longer… Well, it is past summer solstice already! It is true the days are shortening now in the northern hemisphere. But when will the days get longer again? This is a technical puzzle. Like everything solar and astronomical there is no easy answer to the question.

Each year in December the media speak about the shortest day and then go on to say the mornings will still get darker. They are correct but how can this be? I thought I ought to clarify the question for myself if I could. It probably will not relieve anyone’s confusion by starting with a graph, so I have put my own study of the shortest day into an article for The British Sundial Society.

It has turned out a longer read than I expected—A study of the shortest day, Alastair Hunter. BSS Bulletin Volume 31(ii) June 2019