Summer solstice arrives June 21 at 4:24 a.m. ET — When Is The Longest Day Of The Year

The answer to when is the longest day of the year comes on June 21 at 4:24 a.m. ET, when the summer solstice arrives in the Northern Hemisphere. Julia Gomez wrote that the event marks the first day of astronomical summer.

It is also the point when the Northern Hemisphere gets its longest days and shortest nights. The Southern Hemisphere, by contrast, will experience its winter solstice at the same time.

Stonehenge and Newgrange

People gather at Stonehenge to watch the sun peek through its pillars. The site in Wiltshire, England, was built between approximately 3100 and 1600 BC, and thousands still gather there for the solstice.

Stonehenge took on religious significance in the 20th century for people who subscribed to New Age beliefs, including Neopaganism and Neo-Druids. Newgrange in Ireland is one of several other places around the world known for celebrating the solstice.

Earth's 23.5-degree tilt

The seasonal shift follows the way Earth rotates on a 23.5-degree tilt, with the planet's northernmost tip angled toward the sun during the summer solstice. That tilt is what places the date at the center of the year’s astronomical calendar in the Northern Hemisphere.

For anyone tracking the daylight change, June 21 at 4:24 a.m. ET is the point to watch. After that moment, the Northern Hemisphere moves into astronomical summer while the Southern Hemisphere moves into winter.