The winter solstice is often misunderstood regarding when the days begin to lengthen. While the solstice marks the shortest period of daylight, the idea that the entire day shifts symmetrically afterward is a source of confusion. The question of when we start gaining sunlight has a simple answer, but the timing of individual sunrises and sunsets reveals a deeper complexity in how we measure time against the Earth’s orbital mechanics.
Defining the Winter Solstice
The winter solstice is an astronomical event defining the moment when one of Earth’s hemispheres is tilted farthest away from the Sun. This phenomenon typically occurs on December 21st or 22nd in the Northern Hemisphere. It results directly from the planet’s axial tilt of approximately 23.4 degrees relative to its orbital plane. This maximum tilt away causes the Sun to follow its lowest and shortest path across the sky.
This short path means the hemisphere experiencing the solstice receives the minimum amount of daylight for the year, resulting in the longest night. The solstice is not an entire day but a precise instant in time. Afterward, the tilt begins to reverse its angle relative to the Sun. This reversal initiates the slow, gradual process of increasing daylight hours, signaling the astronomical start of winter and the symbolic return of the Sun.
Immediate Gain: Tracking Daylight Duration
The total amount of daylight begins to increase immediately following the winter solstice. On the day after the solstice, the duration between sunrise and sunset is slightly longer than the day before. This increase occurs because Earth moves past the point of maximum tilt away from the Sun, causing the Sun’s daily path to begin moving northward again.
The initial gain is small, often only a matter of a few seconds of daylight added each day. This rate of increase is not constant and accelerates as Earth moves toward the spring equinox. In regions like the northern continental United States, the daily gain may be a few minutes, increasing steadily until the summer solstice is reached.
The Shifting Clock: Why Sunsets and Sunrises Don’t Match
Although the total amount of daylight increases right after the solstice, the times for the earliest sunset and the latest sunrise do not align with this date. The earliest sunset actually occurs several days or even weeks before the solstice, while the latest sunrise happens several days or weeks after the solstice. This asymmetry is a result of a discrepancy between the uniform time kept by mechanical clocks and the variable time measured by the actual position of the Sun in the sky.
The difference between these two timekeeping methods is quantified by a concept called the “Equation of Time.” Our clocks assume every day is exactly 24 hours long, based on the average length of a solar day over the year, known as mean solar time. However, the actual length of a solar day—the time it takes for the Sun to return to the same position in the sky—varies slightly throughout the year.
This variation is caused by two astronomical factors: the Earth’s axial tilt and its elliptical orbit around the Sun. The Earth moves faster in its orbit when it is closer to the Sun in January and slower when it is farther away in July. This changing orbital speed means that around the winter solstice, the true solar day is slightly longer than 24 hours.
Because the solar day is longer than 24 hours in late December, the time of “solar noon”—the point halfway between sunrise and sunset—shifts slightly later each day according to our clocks. This daily delay causes both sunrise and sunset to be pushed later. The combined effect of the increasing daylight duration and the daily delayed solar noon creates the timing quirk.
The increasing length of the day pulls the sunrise earlier and the sunset later, while the shifting solar noon pushes both later. In the weeks leading up to the solstice, the shifting solar noon effect dominates the sunset time, causing it to occur later, which makes the earliest sunset happen in early December. After the solstice, the solar noon continues to shift later, which delays the sunrise time and pushes the latest sunrise into early January. The exact dates for the earliest sunset and latest sunrise vary depending on latitude.