The Winter Solstice: The Science Behind the Shortest Day
Each year in late December, we experience a turning point in Earth’s journey around the Sun: the winter solstice. Often described as the “shortest day of the year,” the winter solstice marks a precise astronomical moment.

What Is the Winter Solstice?
The winter solstice occurs when Earth’s Northern Hemisphere is tilted as far away from the Sun as possible. At this moment, the Sun follows its lowest and shortest path across the sky, resulting in the fewest daylight hours of the entire year.
This isn’t caused by Earth being farther from the Sun, Earth is actually closest to the Sun in early January. Instead, the solstice happens because Earth is tilted about 23.5 degrees on its axis. That tilt controls how much sunlight each hemisphere receives throughout the year.
Why Is It the Shortest Day?
On the winter solstice:
- The Sun rises at its southernmost point on the horizon
- Solar noon is lower in the sky
- Sunlight strikes the Northern Hemisphere at a more indirect angle
All of this reduces both the duration and intensity of sunlight we receive. In much of the continental United States, daylight lasts only about 9–10 hours on the solstice.
When Do We Start Gaining Daylight?
Here’s the hopeful part: the return of the light begins immediately after the winter solstice.
- In the days following the solstice, daylight increases by about 1–2 minutes per day
- By late January, the daily increase can approach 2–3 minutes per day
- The rate continues to increase until around the spring equinox
Interestingly, the latest sunrise doesn’t occur exactly on the solstice, it happens a few days later. This is due to the way Earth’s elliptical orbit and axial tilt interact, a phenomenon known as the equation of time.
How Long Until the Summer Solstice?
From the winter solstice in late December, there are approximately 182 days until the summer solstice, which occurs around June 20–21.
That long arc from shortest day to longest day represents Earth slowly tipping the Northern Hemisphere back toward the Sun—bringing longer days, higher sun angles, and eventually summer warmth.
A Brief History of Solstice Celebrations
Long before modern astronomy, people noticed the solstice’s significance.
- Ancient stone structures like Stonehenge align with solstice sunrises and sunsets
- Roman celebrations such as Saturnalia honored the return of longer days
- Norse cultures observed Yule, a festival centered on light, renewal, and survival
While the traditions varied, the shared theme was universal: the Sun’s return meant hope, food, and life.
High Touch High Tech offers programs demonstrating the Earth’s tilt, solar eclipses, and lunar eclipses through hand-on experiments. We will bring the laboratory to your school! Go to sciencemadefun.io to check for a location near you!
Citations
- National Aeronautics and Space Administration (NASA). Earth’s seasons and axial tilt.
- National Weather Service. Winter solstice and daylight changes.
- Time and Date AS. Daylight length and solstice timing.
- Smithsonian National Museum of Asian Art. Historical solstice observances.
- Royal Museums Greenwich. Solstices and equinoxes explained.






























