The solstice is the 24-hour period during the year when the most daylight hits the Northern Hemisphere
The summer solstice marks the official start of summer. It brings the longest day and shortest night of the year for the 88 percent of Earth’s people who live in the Northern Hemisphere. People around the world observe the change of seasons with bonfires and festivals and Fête de la Musique celebrations.
Astronomers can calculate an exact moment for the solstice, when Earth reaches the point in its orbit where the North Pole is angled closest to the sun. That moment will be at 6:07 a.m. Eastern Time on June 21 this year. From Earth, the sun will appear farthest north relative to the stars. People living on the Tropic of Cancer, 23.5 degrees north of the Equator, will see the sun pass straight overhead at noon. Six months from now the sun will reach its southern extreme and pass overhead for people on the Tropic of Capricorn, and northerners will experience their shortest days of the year, at the winter solstice.
The sun’s angle relative to Earth’s equator changes so gradually close to the solstices that, without instruments, the shift is difficult to perceive for about 10 days. This is the origin of the word solstice, which means “solar standstill.” This slow shift means that June 21 is only about 1 second longer than June 20 at mid-northern latitudes. It will be about a week before there’s more than a minute change to the calculated amount of daylight. Even that’s an approximation – Earth’s atmosphere bends light over the horizon by different amounts depending on weather, which can introduce changes of more than a minute to sunrise and sunset times.
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