The timing of sunrise and sunset changes throughout the year, and the specific dates when the sun rises latest or sets earliest are often unexpected. Many people assume the latest sunrise occurs on the Winter Solstice, the shortest day of the year, but this is incorrect. This misconception overlooks an astronomical effect that offsets the latest sunrise by several weeks from the shortest day. The precise timing is determined by the interplay between Earth’s orbital speed and its axial tilt.
The Exact Timing of the Latest Sunrise
In the Northern Hemisphere, the latest sunrise occurs not in late December, but in the early part of the following year. This event typically occurs between January 3rd and January 7th, varying slightly depending on a location’s latitude. For example, at a latitude of 40° North, the latest sunrise is usually observed around January 5th. This timing is measured using Standard Time, as Daylight Saving Time is not in effect during this period in most regions.
The latest sunrise signifies the point when the sun’s daily clock-time shift reverses direction, causing sunrises to begin occurring progressively earlier. Although the effect is most noticeable in the mid-latitudes, the underlying astronomical reason applies globally.
The Shortest Day Versus the Latest Sunrise
The Winter Solstice, which occurs around December 21st, marks the shortest period of daylight and the longest night of the year. While the Solstice features the shortest day, it does not hold the record for the latest sunrise. The earliest sunset happens even earlier, usually in early December, several weeks before the Solstice. This separation between the earliest sunset, the shortest day, and the latest sunrise is a result of the sun’s apparent movement not being perfectly uniform across the sky.
The latest sunrise occurs because the time of “solar noon”—the exact moment the sun reaches its highest point in the sky—is continually shifting later each day during this winter period. Even though the amount of daylight is increasing after the Solstice, the entire day, including sunrise and sunset, is still being pushed later by this shifting solar noon.
Why the Time Shifts (The Equation of Time)
The primary reason for the mismatch between our clocks and the sun’s apparent position is a phenomenon called the Equation of Time. This term describes the difference between time measured by a clock (mean solar time) and time measured by a sundial (apparent solar time). The length of a true solar day, measured from one solar noon to the next, is not always exactly 24 hours, fluctuating throughout the year.
Two main astronomical factors cause this fluctuation in the solar day length. The first is the elliptical shape of Earth’s orbit around the sun. In early January, Earth reaches perihelion, its closest point, causing it to move fastest in its orbit. This increased speed means the Earth has to rotate slightly more on its axis to bring the sun back to the same apparent position, making the solar day longer than 24 hours during this time.
The second factor is the 23.4-degree tilt of the Earth’s axis relative to its orbital plane (the obliquity of the ecliptic). The angle of the sun’s path across the sky changes throughout the year due to this tilt. The combination of the Earth’s fastest orbital speed and the axial tilt effects is greatest around the Winter Solstice. This causes the apparent sun to run “slow” compared to our clocks in December and January, delaying both sunrise and solar noon. This cumulative delay effect pushes the latest sunrise into the new year, even after the days have begun to lengthen.
How Geography and Time Zones Affect Observation
While the astronomical reasons for the latest sunrise are the same everywhere, the exact time shown on a clock varies significantly based on geographic location. The most influential factor is a location’s specific longitude relative to the center of its designated time zone. Each time zone spans 15 degrees of longitude, but their boundaries are often drawn along political lines.
A location situated on the far western edge of a time zone will experience all solar events, including the latest sunrise, later by clock time than a location on the far eastern edge. Because the Earth rotates four minutes for every degree of longitude, this longitudinal effect can easily mask the subtle annual shift in sunrise time. Latitude also plays a role, as the magnitude of the overall sunrise/sunset shift throughout the year is more pronounced the closer a location is to the poles.