Daylight hours refer to the period each day from sunrise to sunset. Many people notice the shortening days as autumn progresses into winter and often wonder when the trend will reverse.
The Winter Solstice: The Turning Point
Daylight hours begin to increase in the Northern Hemisphere immediately following the Winter Solstice. This astronomical event marks the Northern Hemisphere’s shortest day and longest night of the year, typically occurring around December 21st or 22nd annually.
The Winter Solstice signifies the moment Earth’s Northern Hemisphere is tilted farthest away from the Sun. After this point, the tilt gradually shifts, leading to more direct sunlight and longer days. While the change is subtle at first, becoming more noticeable by late January or February, more daylight consistently returns. Conversely, in the Southern Hemisphere, the December solstice marks their summer solstice, experiencing their longest day of the year.
Why Daylight Hours Change
The primary reason for the changing length of daylight hours is Earth’s axial tilt combined with its orbit around the Sun. Earth is tilted on its axis by approximately 23.5 degrees relative to its orbital plane. This tilt means that as Earth revolves around the Sun, different parts of the planet receive varying amounts of direct sunlight.
When the Northern Hemisphere tilts towards the Sun, it experiences summer and longer days; when it tilts away, it experiences winter and shorter days. This constant tilt, rather than Earth’s distance from the Sun, is the fundamental cause of the seasons and the variations in day length across the globe.
The Path to Maximum Daylight
Daylight hours steadily increase after the Winter Solstice, progressing towards the Spring Equinox. The Spring or Vernal Equinox occurs around March 20th or 21st, when day and night are roughly equal in length across most of the world. This period sees a significant gain in daylight, particularly noticeable in higher latitudes.
The lengthening of days continues past the Spring Equinox, leading up to the Summer Solstice. The Summer Solstice, occurring around June 20th or 21st in the Northern Hemisphere, marks the longest day of the year. Following the Summer Solstice, the cycle reverses, and daylight hours gradually begin to shorten once more.