It’s a common question many of us ask as the days grow shorter and winter approaches – will the days ever start getting longer again? The simple answer is yes, the days will eventually start to lengthen after the winter solstice in late December. But to fully understand why the days get shorter and longer over the course of a year, we need to explore some basic astronomy concepts.
What causes the seasons?
The seasons are caused by the tilt of the Earth’s axis of rotation relative to the plane of its orbit around the sun. Here’s a quick explanation:
- The Earth rotates on an axis that is tilted 23.5 degrees relative to the plane of its orbit around the sun
- As the Earth orbits the sun over the course of a year, its tilted axis always points in the same direction
- So in June, the Northern Hemisphere is tilted towards the sun, resulting in more direct sunlight and warmer temperatures – this is summer
- In December, the Southern Hemisphere is tilted towards the sun, resulting in winter in the Northern Hemisphere
This tilt is what causes the seasons, as either hemisphere receives more direct sunlight during its summer months and less during its winter. The tilt also impacts the length of days over the course of the year.
Why do days get shorter leading up to winter?
As we approach winter in the Northern Hemisphere, the days get progressively shorter. Why does this happen?
- As the Earth orbits the sun, the Northern Hemisphere gradually tilts away from the sun’s direct rays
- This means the sun follows a lower path across the sky each day
- In June, the sun is high in the sky, resulting in about 15 hours of daylight in the Northern Hemisphere
- In December, the sun stays lower in the sky, resulting in only about 9 hours of daylight
So the further the Northern Hemisphere tilts away from the sun, the shorter the days become, culminating in the winter solstice in late December – the day with the least amount of sunlight.
When do days start getting longer again?
After the winter solstice, the process reverses itself and days start to lengthen again in the Northern Hemisphere. Here’s why:
- Around December 21-22, the North Pole is tilted as far away from the sun as it gets
- After the winter solstice, the Northern Hemisphere starts tilting back toward the sun
- This allows the sun to take a slightly higher path across the sky each day
- So in January, there’s a bit more daylight each day compared to December
- This increase in daylight each day continues until the summer solstice in June
So in the Northern Hemisphere, the shortest day of the year marks a turning point – after that, we gain a little bit more sunlight each day as we tilt back toward the sun.
A table showing daylight hours
To visualize how daylight hours change over the course of the year, here’s a table for a location at 40° N latitude:
| Date | Daylight Hours |
|---|---|
| June 21 (summer solstice) | 15 hours |
| September 21 (fall equinox) | 12 hours |
| December 21 (winter solstice) | 9 hours |
| March 21 (spring equinox) | 12 hours |
As you can see, the daylight hours are longest on the summer solstice in June. They get progressively shorter leading up to the winter solstice in December, which has the least amount of daylight. After December 21, the daylight hours start increasing again each day.
Does location affect day length?
Yes, location affects how much daylight you experience throughout the year. Here’s why:
- Places at higher latitudes (farther from the equator) experience more extreme variations in day length
- For example, Helsinki, Finland at 60°N has 19 hours of daylight in June and only 6 hours in December
- Places near the equator like Singapore have a constant 12 hours of daylight all year long
- The further north or south you are from the equator, the more day length varies over the seasons
So if you live far north of the equator, like in Alaska or Scandinavia, you’ll experience very long summer days and very short winter days. If you live near the equator, the amount of daylight remains fairly consistent year-round.
Daylight variation by latitude
Here’s a table showing how daylight hours vary by latitude on the summer and winter solstices:
| Latitude | June 21 daylight | December 21 daylight |
|---|---|---|
| 80°N (Northern Alaska) | 24 hours | 0 hours |
| 60°N (Helsinki, Copenhagen) | 19 hours | 6 hours |
| 40°N (New York, Madrid) | 15 hours | 9 hours |
| Equator (Singapore, Ecuador) | 12 hours | 12 hours |
As you can see, the further north you are, the more daylight you experience in summer vs. winter. This effect is most dramatic inside the Arctic Circle above 66°N.
When do equinoxes occur?
Equinoxes are the two days a year when day and night are equal length worldwide. They occur in March and September:
- March Equinox – around March 21, marks the start of spring in the Northern Hemisphere
- September Equinox – around September 21, marks the start of fall
- On these days, the sun is exactly above the equator, so daylight and night are equal length (12 hours)
- Equinoxes are the midpoint between solstices – half a year before/after the summer and winter solstices
After the March equinox, days start becoming longer than nights in the Northern Hemisphere as we head towards summer. After the September equinox, nights start becoming longer as winter approaches.
Does the winter solstice always occur on December 21?
Not exactly. While the winter solstice usually occurs on December 21st or 22nd, the exact date can vary slightly from year to year. Here’s why:
- The Earth takes 365.24 days to orbit the sun – but our calendar years are 365 days
- So the winter solstice can occur anywhere from December 20-23 to “catch up” with the Earth’s position
- In 2020, the winter solstice occurred on December 21
- In 2021, it occurred on December 21
- In 2022, it will fall on December 21
- In 2023, it will occur on December 22
So while it usually falls on the 21st, the exact date shifts around slightly. December 21 or 22 are the most common dates.
Upcoming winter solstice dates
| Year | Winter solstice date |
|---|---|
| 2023 | December 22 |
| 2024 | December 21 |
| 2025 | December 21 |
| 2026 | December 21 |
| 2027 | December 22 |
As you can see, while usually on the 21st, it can vary by a day depending on the year and how the dates align with the solar calendar.
Will days keep getting longer after the summer solstice?
No, the pattern reverses itself again after the summer solstice in June. Here’s what happens:
- Around June 21, the North Pole tilts most directly towards the sun – giving us the longest daylight hours
- After June 21, the Northern Hemisphere starts tilting away again, causing days to get progressively shorter
- This leads to the September equinox, when day and night are equal length again
- Days continue shortening until the December winter solstice, and the cycle repeats
So the longest day of the year in June marks a turning point – after that, days start to shorten again as we head back towards winter. It’s an endless cycle caused by the tilt of the Earth’s axis as we orbit the sun.
Will days keep getting longer each year?
In the short term, the length of days at solstices and equinoxes will remain stable from one year to the next. However, over millennia, the Earth’s axis tilt and rotation are slowly changing, causing very gradual shifts in day lengths. Here are some key points:
- Currently the tilt is 23.5 degrees – but it varies between 22.1 and 24.5 degrees over a 41,000 year cycle
- When tilt is less, seasonal contrasts are less extreme (shorter winter days)
- The direction Earth’s axis points also shifts over a 26,000 year cycle
- These subtle shifts affect when seasons occur and cause day lengths to change ever so slightly over thousands of years
So in our lifetime, seasonal day lengths will appear constant year to year. But over the course of future millennia, astronomers predict gradual shifts of up to 20 minutes in solstice and equinox day lengths due to slow changes in Earth’s axial tilt and rotation.
Conclusion
In summary, the recurring cycle of longer and shorter days over the year is driven by the tilt of the Earth’s axis as we orbit the sun. The winter solstice marks the shortest day of the year – after that point, we gain progressively more daylight each day until summer. While the exact winter solstice date can vary year to year, the pattern of decreasing and increasing daylight repeats annually. And though tiny changes may occur over thousands of years, this cycle of seasons and daylight will continue far into the future.