The summer solstice arrives Sunday, marking the longest day of the year in the Northern Hemisphere and signaling the official start of astronomical summer. For those in the Southern Hemisphere, it signifies the shortest day and the beginning of winter.
The term "solstice" originates from Latin words meaning "sun" and "stop," referring to the sun's apparent pause in its highest arc across the sky before beginning its descent. This year, the solstice falls on June 21, a date that typically occurs between June 20 and 22.
Earth's orbit around the sun is tilted, causing uneven distribution of sunlight between the Northern and Southern Hemispheres throughout the year. The solstices represent the points at which this tilt is most extreme, resulting in the greatest difference in daylight hours between the two hemispheres.
During the Northern Hemisphere's summer solstice, the planet's upper half leans towards the sun, maximizing daylight. Conversely, the Northern Hemisphere's winter solstice, occurring between December 20 and 23, sees the upper half leaning farthest away from the sun, resulting in the shortest day and longest night.
The year is also divided by equinoxes, when Earth's tilt is neutral relative to the sun, providing nearly equal daylight and darkness across both hemispheres. The autumnal equinox in the Northern Hemisphere typically falls between September 21 and 24, while the vernal equinox occurs between March 19 and 21. These moments align with the sun being directly overhead at the equator.
These astronomical markers differ from meteorological seasons, which are defined by three-month periods based on annual temperature cycles. Under the meteorological calendar, spring begins March 1, summer on June 1, fall on September 1, and winter on December 1.