Sky Matters: Shortest day of the year happens this month — or maybe August
Since we don’t know what’s causing the Earth to spin faster, we can’t exactly predict what happens next. Pictrure: iStock
If asked to name the shortest day of the year, most of us would plump for December 21. It’s the sort of slam-dunk pub-quiz question designed to lull us into a false sense of “knowing stuff” – or perhaps that’s just me and pub quizzes. But the answer, surprisingly, is not December 21, but rather July 9 or possibly July 22 or maybe even August 5, at least in 2025.
To resolve this apparent conundrum, we first have to define what is meant by a “day”. If it was the time between sunrise and sunset, then December 21 would be the correct answer. If it is the time taken for the Earth to spin once on its axis then it's more complicated, leading to the three possible dates in July and August.
