Today marks the June, or summer solstice in the Northern Hemisphere. It's the longest day of the year and the beginning of astronomical summer. Solstice comes from the Latin solstitium, meaning “sun standing still.” The Earth continues to move, but the sun’s apparent movement across our sky nearly does.
Since December, the sun has been climbing higher in the midday sky while rising and setting farther north along the horizon. Days have been steadily growing longer as a result. Those changes are easy to notice through the winter and spring, but as the June solstice approaches, both the sun’s northward movement and the daily increase in daylight begin to slow dramatically.
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By the time the solstice arrives, the difference in the sun’s position from one day to the next is almost imperceptible. In Raleigh, the sun reaches its highest noon altitude of the year, about 76 degrees above the horizon. The length of daylight also reaches its annual maximum at about 14 hours and 35 minutes. Yet even that change has nearly stalled. Around the solstice, the day-to-day difference in sunrise, sunset, and total daylight amounts to only a few seconds.
This happens because Earth is tilted about 23.5 degrees relative to its orbit around the sun. At the June solstice, the Northern Hemisphere reaches its maximum tilt toward the sun, placing the sun at its northernmost position in our sky. With nowhere farther north to go, its apparent motion, as well as the rate at which daylight is increasing, slows to a crawl before reversing direction.
Ancient skywatchers noticed this long before they understood why it happened. By tracking where the sun rose and set, they observed that its movement slowed, stopped, and then reversed. They likely noticed the same pause in the changing length of day. For several days around the solstice, the amount of daylight changes so little that it seems almost frozen in place before beginning its gradual return in the opposite direction.
The solstice is therefore more than just the longest day of the year. It is a celestial turning point, a brief pause in two annual cycles. The sun’s march northward has reached its limit, and the steady lengthening of daylight has come to an end. Beginning tomorrow, both will slowly reverse course as the Northern Hemisphere starts its long journey back toward winter.
