The winter solstice is the shortest day, but the earliest sunsets come a couple of weeks before the solstice, in early to mid-December, depending on your latitude. What’s more, the latest sunrises come after the winter solstice, in January.

Why isn’t the earliest sunset on the year’s shortest day? It’s because a clock ticks off exactly 24 hours from one noon to the next, while the actual days – as measured by the spin of the Earth – are rarely exactly 24 hours long.

One Earth spin can be measured from what is called one “solar noon” or “midday” to the next. Solar noon refers to that instant when the sun reaches its highest point for the day. At this time of year, the time period from one solar noon to the next is actually half a minute longer than 24 hours. So – two weeks before the solstice, for example – the sun reaches its noontime position at 11:52 a.m. local standard time. Two weeks later – on the winter solstice – the sun reaches its noontime position at 11:59 a.m. That’s 7 minutes later.

The later clock time for solar noon also means a later clock time for sunrise and sunset. The result: earlier sunsets before the solstice and increasingly later sunrises for a few weeks after the solstice.

By the way, the exact date of earliest sunset varies with latitude. But the sequence is always the same: earliest sunset in early December, winter solstice, latest sunrise in early January.

Here’s more detail about the earliest sunsets.