The longest day of the year, the summer solstice, is commonly believed to host the year’s latest sunset. While the solstice marks the peak of daylight hours, the latest moment the sun dips below the horizon actually occurs several days or weeks afterward. This discrepancy arises because the timing of the sun’s daily path is not perfectly aligned with the steady 24-hour cycle of our clocks. The Earth’s complex motion causes a subtle yet measurable shift in when solar noon—the moment the sun reaches its highest point—occurs each day. This misalignment explains why the sunset continues to get later even after the days have begun to shorten.
Identifying the Latest Sunset Dates
The specific date of the latest sunset shifts depending on a location’s latitude and hemisphere. In the Northern Hemisphere, the summer solstice typically falls around June 21st, but the latest sunset occurs approximately one to two weeks later, usually in early July. For a location at a mid-northern latitude, such as 40° North, the latest sunset may occur around June 28th, a full week after the longest day of the year.
Conversely, in the Southern Hemisphere, the longest day is the December Solstice, around December 21st. The latest sunset there occurs in early January, following a similar delay pattern. The latest annual sunset is always associated with the summer period.
The phenomenon is also observed around the winter solstice, although the focus shifts to the earliest sunset. In the Northern Hemisphere, the earliest sunset of the year arrives in early December, often around December 8th, before the winter solstice on December 21st.
The Astronomical Reason for the Delay
The reason for the delayed latest sunset lies in the difference between clock time and the true time dictated by the sun, a factor scientists quantify with the “Equation of Time.” Our standard 24-hour day is based on the average length of a solar day throughout the year. However, the actual time it takes for the sun to return to the same position in the sky—a true solar day—is not exactly 24 hours.
This variation is caused by two astronomical factors working in combination. The first is the Earth’s axial tilt, which is responsible for the changing seasons and the varying length of daylight. The second is the Earth’s elliptical orbit around the sun.
The Earth moves faster in its orbit when it is closest to the sun, a point called perihelion, which occurs in early January. It moves slowest when it is farthest away, at aphelion, which occurs in early July. Because of this varying speed, the Earth has to rotate a slightly different amount each day for the sun to appear in the same position.
Around the time of the summer solstice, the varying orbital speed causes the solar day to be slightly longer than 24 hours. This means solar noon, the moment the sun is highest in the sky, arrives a few minutes later each day by clock time. This shift in solar noon is what delays the sunset.
Even though the total length of daylight is decreasing after the solstice, the sun’s highest point is still occurring later on the clock. This later solar noon effectively pushes the entire day’s solar events, including sunset, later until the orbital mechanics reverse this trend. The combination of the day length decreasing and the solar noon shifting later determines the exact date of the latest sunset.
Latest Sunrise vs. Latest Sunset
The delayed latest sunset is part of a larger pattern where the times of sunrise and sunset do not change symmetrically around the solstices. While the latest sunset happens after the summer solstice, the earliest sunrise of the year actually happens before it. For example, at a mid-northern latitude, the earliest sunrise may occur around June 14th, about two weeks before the latest sunset.
This asymmetry is most noticeable around the winter solstice, the shortest day of the year. The earliest sunset occurs well before the winter solstice, typically in early December. In contrast, the latest sunrise of the year occurs weeks after the winter solstice, usually in early January.
The shifting solar noon, driven by the Equation of Time, affects both sunrise and sunset times. Around the winter solstice, the day length is still slightly decreasing, but the solar noon continues to shift later, pushing the sunrise time later into January.
How Daylight Saving Time Alters Observation
The human practice of Daylight Saving Time (DST) further complicates the observation of the latest sunset. DST is a convention where clocks are moved forward by one hour during the warmer months, artificially extending the evening light. This clock shift does not change the physical astronomical event of sunset, but it significantly alters the time displayed on the clock.
When DST is in effect, the latest sunset that naturally occurs in early July appears an hour later than it would under Standard Time. The one-hour clock adjustment is superimposed on the natural solar delay caused by the Equation of Time. Therefore, the latest observed clock time for sunset is a combination of the natural astronomical delay and the human-imposed DST shift.