Tracking daylight: Minnesota sunsets shift later in less than a month

We’re moving through the darkest days of the year in Minnesota. It’s the time of year where on cloudy days it feels like it starts getting dark shortly after lunchtime.

Later sunsets begin Dec. 14

December sunset times in Minnesota are interesting to watch. Our earliest sunsets actually occur from the end of November into mid-December. The earliest sunsets of the year actually occur before the winter solstice.

In the Twin Cities, sunset time holds at 4:31 p.m. from Dec. 4 through Dec. 13 according to timeanddate.com.

Then starting on Dec. 14, sunset times shift ever so slightly move later. Our 4:34 sunset time is actually 3 minutes later by the December solstice on Dec. 21. And with our sunset at 4:41 p.m. on Dec. 31 we gain a full 10 minutes of evening daylight by the end of the year.

These small changes are hard to notice at first. But by Christmas and New Year’s, it’s easy to notice the growing daylight in the evening hours on sunny days.

The flip side of Minnesota’s daylight coin is later sunrises in the morning hours. The latest sunrises actually occur after the winter solstice during the last days of December into early January.

Earth’s axis and orbit

Seasonally speaking, most extreme sunrise and sunset times don’t match up precisely with the solstices. That’s because the Earth’s orbit is an ellipse, and the Earth’s axis is tilted. The orientation between the Earth and sun causes subtle shifts in the time the sun rises and sets around the solstices.

Like many things about our Earth, the reasons for shifting sun times are complicated. Here’s a good explanation of why our sunrise and sunset times vary from the solstices from Earthsky:

The December solstice marks the shortest day of the year in the Northern Hemisphere and longest day in the Southern Hemisphere. But the earliest sunset – or earliest sunrise if you’re south of the equator – happens before the December solstice. Many people notice this, and ask about it.

The key to understanding the earliest sunset is not to focus on the time of sunset or sunrise. The key is to focus on what is called true solar noon – the time of day that the sun reaches its highest point in its journey across your sky.

In early December, true solar noon comes nearly 10 minutes earlier by the clock than it does at the solstice around December 21. With true noon coming later on the solstice, so will the sunrise and sunset times.

It’s this discrepancy between clock time and sun time that causes the Northern Hemisphere’s earliest sunset and the Southern Hemisphere’s earliest sunrise to precede the December solstice.

The discrepancy occurs primarily because of the tilt of the Earth’s axis. A secondary but another contributing factor to this discrepancy between clock noon and sun noon comes from the Earth’s elliptical – oblong – orbit around the sun. The Earth’s orbit is not a perfect circle, and when we’re closest to the sun, our world moves fastest in orbit. Our closest point to the sun – or perihelion – comes in early January. So we are moving fastest in orbit around now, slightly faster than our average speed of about 18.5 miles per second (30 kilometers per second). The discrepancy between sun time and clock time is greater around the December solstice than the June solstice because we’re nearer the sun at this time of year.

So keep an eye out in mid-December. Minnesota’s sunsets start getting slightly later again in less than a month.