The Shortest Day of the Year in the Northern Hemisphere
Updated: 1 day ago
The December Solstice The shortest day of the year in the Northern Hemisphere occurs during the December solstice, an astronomical phenomenon that takes place between 20 and 22 December, according to the Gregorian calendar. In 2024, the solstice was recorded on 21 December, at 09:21 (Lisbon time) and 10:21 (Madrid time). This event marks the beginning of winter in the Northern Hemisphere and of summer in the Southern Hemisphere.
The December solstice corresponds to the moment when the Sun reaches its lowest declination relative to the Celestial Equator in the Northern Hemisphere, resulting in the day with the fewest hours of sunlight and the longest night of the year.
What is the solstice?
The word "solstice" comes from the Latin solstitium, formed from solis (sun) and sistere (to stand still), referring to the apparent "halt" of the Sun in the sky. During this phenomenon, the position of the Sun at sunrise and sunset seems to remain constant, marking a reversal in the apparent movement of its path.
This phenomenon is due to the tilt of the Earth's axis (approximately 23.5 degrees relative to the orbital plane), which causes the Sun's rays to strike the different regions of the planet unevenly over the course of the year.
Characteristics of the December solstice in the Northern Hemisphere
Shortest day of the year: The December solstice brings the fewest hours of daylight, which vary with latitude. The further north you are, the shorter the day and the longer the night.
Lowest height of the Sun in the sky: At solar noon, the Sun reaches its lowest position above the horizon of the entire year.
Beginning of winter: This phenomenon marks the official start of the coldest season in the Northern Hemisphere, even though the coldest weather arrives weeks later because of thermal lag.
Symmetry with the Southern Hemisphere
In the Southern Hemisphere, the December solstice brings the opposite phenomenon to that of the Northern Hemisphere. While the North experiences the shortest day of the year and the beginning of winter, the South has the longest day of the year, marking the official start of summer. This difference results from the Earth's axial tilt, which distributes sunlight unevenly between the two hemispheres over the year.
Cultural and historical importance
Since ancient times, the December solstice has been celebrated by many cultures as a moment of renewal and rebirth, given the gradual return of sunlight in the days that follow.
Saturnalia (Ancient Rome): A festival dedicated to the god Saturn, associated with the harvest cycle and the rebirth of the Sun.
Yule (Germanic peoples): Festivities in honour of the Sun and of the hope for the return of longer days.
Christmas: Many Christmas traditions have their roots in solstice celebrations, representing light overcoming darkness.
Astronomy and science
At the December solstice, the Tropic of Capricorn, at 23.5° south latitude, receives the Sun's rays perpendicularly. This astronomical alignment results in the Earth's maximum tilt, with the Northern Hemisphere inclined away from the Sun.
Climate impact: seasonal lag
Although the December solstice marks the beginning of winter, the lowest temperatures usually occur a few weeks later. This phenomenon, known as seasonal lag, is due to the thermal capacity of the oceans and the atmosphere, which take longer to cool in response to the reduced solar radiation.
Curiosities about the December solstice
The length of the day at the solstice varies with location. In Lisbon, the day lasts about 9 hours, while in Arctic regions there may be no daylight at all.
After the solstice, the days gradually grow longer until the spring equinox in March.
Sites such as Stonehenge, in the United Kingdom, and Machu Picchu, in Peru, have architectural alignments that celebrate the solstices.
The December solstice is an astronomical and cultural milestone that symbolises transition and the cycle of nature. This day, with its long night and short daylight, inspires the celebration of the return of light and the start of a new annual cycle.
Timepieces and solstices
Sundials
Sundials were widely used to indicate the position of the Sun in the sky, and some were designed to mark the solstices:
Analemmatic sundials: They use the position of the Sun throughout the year, with specific points for the summer and winter solstices.
Vertical or horizontal gnomons: The shadow cast by a gnomon can be used to identify the solstice when it reaches its maximum or minimum position along a specific line.
Astronomical Clocks
Complex astronomical clocks, such as those that can be seen in some cathedrals and historic squares, incorporate solar calendars that indicate the dates of important astronomical events, such as the solstices.
Orloj - Prague
Orloj - Prague Astronomical Clock: Displays solar, lunar and seasonal information, as well as the time.
Strasbourg Astronomical Clock: Shows representations of the Sun's movement in relation to the seasons.
Megalithic Sundials and Alignments
Newgrange and Stonehenge
Monuments such as Stonehenge, in the United Kingdom, or Newgrange, in Ireland, have specific alignments with the solstices and work as primitive "sundials".
Modern Watches with Astronomical Complications
Watches such as the Vacheron Constantin Les Cabinotiers Celestia can also feature astronomical complications that indicate the solstices and equinoxes:
Watches with an annual or perpetual calendar: Some advanced horological models take detailed astronomical scales into account.
Solar complications: Some pieces indicate the solar declination, a complication known as the equation of time, as well as other phenomena linked to the cycles of the Sun.
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