One Month After the December Solstice: What’s Changing?

How Are Daylengths Changing?

Our thoughts often turn to the Sun around the solstices and equinoxes, when daylengths around the world are at either their most extreme or their most equal.

How about in between these dates? Subtle changes in the Sun’s movement across the sky are going on throughout the year. Around the solstices, these changes happen more slowly; close to the equinoxes, they happen more quickly.

What does this all mean for you? We thought we’d check in and catch up with what the Sun’s doing on January 21, 2026—exactly one month on from the December solstice.

We’ll take a look from the perspective of Chicago in the Northern Hemisphere, and Melbourne in the Southern Hemisphere. And we’ll go to Nairobi to see what’s happening at the equator.

We’ll see that daylengths in Chicago and Melbourne have only changed by around half an hour during the month since December 21. But the pace of change is getting quicker: During the next month, up to February 21, daylengths in Chicago and Melbourne will change by more than an hour.

What Is the Subsolar Point?

But first, let’s step back and ask: Why do things change at all?

Astronomers don’t define solstices and equinoxes by daylengths. Instead, they look at the position of the subsolar point. This is the spot on the globe where the Sun is directly overhead.

The Earth is spinning, so the subsolar point is always on the move, travelling from east to west along a particular line of latitude. (Lines of latitude are the horizontal grid lines we can see on maps of the world.)

Crucially, the Earth is tilted, so the subsolar point moves up and down over the course of the year—from the Southern Hemisphere to the Northern Hemisphere and back again. This north/south movement is what gives us solstices and equinoxes.

• At the December solstice, the latitude of the subsolar point is 23.4 degrees south: directly above the Tropic of Capricorn (which passes through South America, southern Africa, and Australia)
• At the March equinox, the latitude of the subsolar point is zero degrees: directly above the equator
• At the June solstice, the latitude of the subsolar point is 23.4 degrees north: directly above the Tropic of Cancer (which passes through Mexico, northern Africa, the Middle East, India, and China)
• At the September equinox, the latitude of the subsolar point is zero degrees: directly above the equator for the second time in the year

So Where Is the Sun Now?

What’s the latitude of the subsolar point around January 21? We’re roughly one-third of the way between the December solstice and the March equinox, so we might imagine it would be around 15.6 degrees south (23.4 degrees minus a third). But that’s not the case.

In fact, the latitude of the subsolar point on January 21 is around 19.8 degrees south. On a map, that line of latitude is still pretty close to the Tropic of Capricorn.

This is a way of showing that the speed at which the subsolar point moves northward and southward varies over the course of the year. Either side of the solstices, the north/south movement is slow—and, on the day of solstice itself, it comes to a complete stop. Either side of the equinoxes, the up/down movement is quick—in the space of just 24 hours, it can shift by up to 0.4 degrees.

In turn, this affects how quickly things change in towns and cities around the world.

What’s Happening in the Northern Hemisphere?

Let’s take our first example and go to Chicago, at a latitude of 41.9 degrees north in the Northern United States.

On January 21, the Sun rises at 07:12 (7:12 am), reaches its highest point in the sky at 12:01 (12:01 pm), and sets at 16:51 (4:51 pm). This gives Chicago a daylength of around 9 hours and 39 minutes.

If we go back a month to December 21, Chicago’s daylength on the Northern Hemisphere‘s shortest day of the year was only 32 minutes different: 9 hours and 7 minutes. But if we jump forward a month to February 21, the daylength is 10 hours and 53 minutes: a change of 1 hour and 14 minutes.

Daylength is not the only thing that’s changing. Each day, the Sun is climbing a bit higher in the winter sky—and, again, the change is quickening. Around midday on December 21 in Chicago, the Sun reached an altitude of 25°. On January 21 it’s 28°; on February 21 it will be 38°.

One more thing: The points on the horizon where the Sun rises and sets are moving northward with increasing speed. On December 21, the Sun rose in Chicago at 121° (an east-southeast direction). On January 21 it’s 116°, while on February 21 it will be 103°.

And in the Southern Hemisphere?

Now let’s go to our second example, Melbourne, at a latitude of 37.8 degrees south in Southern Australia.

On January 21, the Sun rises at 06:20 (6:20 am), reaches its highest point at 13:31 (1:31 pm), and sets at 20:41 (8:41 pm). This gives Melbourne a daylength of around 14 hours and 20 minutes.

Again, if we go back a month to December 21, Melbourne’s daylength on the Southern Hemisphere’s longest day of the year was just 27 minutes different: 14 hours and 47 minutes. But again jumping forward a month to February 21, the daylength is 13 hours and 15 minutes: a change of 1 hour and 5 minutes.

Likewise, we can again see quickening changes in how high the Sun climbs into Melbourne’s summer sky: 76° on December 21, 72° on January 21, and 63° on February 21.

And in Melbourne the points on the horizon where the Sun rises and sets are moving northward in an almost identical way to Chicago: The Sun rises at 121° (east-southeast) on December 21, 116° on January 21, and 104° on February 21.

Meanwhile at the Equator

What about our third example, Nairobi? Kenya’s capital city sits almost on the equator, at a latitude of 1.3 degrees south.

Around the equator, the rules are different: Almost every day is like an equinox, with a daylength of roughly 12 hours. On January 21, the Sun rises at 06:38 (6:38 am) and sets at 18:49 (6:49 pm), giving Nairobi a daylength of around 12 hours and 10 minutes.

And so it goes every day of the year in Nairobi. Let’s jump all the way forward to June 21—around the June solstice—which is the most extreme difference to January 21 we can find. The Sun rises at 06:33 (6:33 am) and sets at 18:35 (6:35 pm), producing a daylength of 12 hours and 2 minutes.

Bottom Line: Changes Are Speeding Up

In January, daylengths are becoming longer in the Northern Hemisphere, and shorter in the Southern Hemisphere—and these changes are happening with increasing speed. Meanwhile at the equator, little changes: The daylength is roughly 12 hours on every day of the year.