Sunday marks the sun’s ultimate time to shine as the Northern Hemisphere experiences the longest day of the year. This event is the summer solstice, signaling the official start of astronomical summer north of the equator. Conversely, the Southern Hemisphere will experience its shortest day, ushering in the arrival of winter.
Deriving from the Latin words sol (sun) and stitium (to stop or pause), the “solstice” represents the peak of the sun’s annual journey across the sky, where it forms its longest and highest arc. For sun lovers, however, the event brings a bittersweet reality: following the solstice, the sun begins its gradual retreat, and days will steadily shorten until late December.
Humans have celebrated this celestial milestone for millennia through festivals and monuments. Sweden’s vibrant Midsummer celebrations and the ancient pillars of Stonehenge—precisely engineered to align with the sun’s path during both solstices—stand as enduring testaments to this history.
The phenomenon is driven by the Earth’s axial tilt. As the planet orbits the sun, it does so at an angle, causing sunlight and warmth to fall unequally across the northern and southern halves for most of the year. The solstices mark the exact moments when the Earth is tipped most extremely either toward or away from the sun, creating the greatest disparity between day and night.
During the Northern Hemisphere’s summer solstice, which typically lands between June 20 and 22, the top half of the planet leans directly toward the sun. In contrast, the winter solstice (occurring between December 20 and 23) marks the point where the northern half leans furthest away, resulting in the shortest day and longest night.
The solstices differ fundamentally from the equinoxes. Derived from the Latin for “equal night,” an equinox occurs when the Earth’s tilt is neutral relative to the sun, distributing sunlight equally across both hemispheres. On these days, the sun rises almost exactly due east and sets due west, making day and night nearly identical in length. The vernal (spring) equinox occurs between March 19 and 21, while the autumnal (fall) equinox lands between September 21 and 24, marking the precise moment the sun sits directly over the equator.
While astronomical seasons depend on how the Earth moves around the sun, meteorological seasons are defined by the weather. Meteorologists break down the year into three-month seasons based on annual temperature cycles. By that calendar, spring starts on March 1, summer on June 1, fall on Sept. 1 and winter on Dec. 1.
