Understanding the Solstice: The Longest Day in the Northern Hemisphere

Sunday marks the longest day of the year in the Northern Hemisphere, known as the solstice. This event signifies the start of astronomical summer north of the equator. In the Southern Hemisphere, it marks the shortest day and the beginning of winter.

The term “solstice” derives from the Latin “sol,” meaning sun, and “stitium,” meaning pause or stop. The summer solstice is when the sun reaches its highest arc and makes the longest journey across the sky. Following this, the sun appears to retreat, resulting in shorter days until late December.

Historically, solstices have been celebrated worldwide with festivals and monuments. For instance, Sweden holds midsummer eve celebrations, and Stonehenge aligns with the sun’s path during the solstices.

The Earth’s orbit causes these annual events. As the Earth orbits the sun, its tilt ensures unequal distribution of the sun’s warmth and light across the northern and southern hemispheres.

The solstices mark when the Earth tilts most toward or away from the sun. During the Northern Hemisphere’s summer solstice, the upper half of the Earth leans toward the sun, creating the longest day of the year, usually between June 20 and 22. This year, it falls on June 21.

The winter solstice occurs when the Northern Hemisphere leans farthest from the sun, resulting in the shortest day and the longest night, usually between December 20 and 23.

Equinox Explained

During the equinox, neither hemisphere tilts toward or away from the sun, resulting in nearly equal daylight in both hemispheres. The sun rises due east and sets due west.

The term “equinox” is from Latin words meaning equal and night, reflecting that day and night are almost equal in length. The fall equinox occurs between September 21 and 24, while the spring equinox happens between March 19 and 21. The exact equinox occurs when the sun is directly overhead at the equator.

Differences Between Meteorological and Astronomical Seasons

Astronomical seasons rely on Earth’s orbit around the sun. Meteorological seasons are based on annual temperature cycles. Meteorologists divide the year into three-month seasons: spring begins March 1, summer on June 1, fall on September 1, and winter on December 1.

The Associated Press Health and Science Department is supported by the Howard Hughes Medical Institute’s Department of Science Education and the Robert Wood Johnson Foundation. The AP maintains sole responsibility for its content.