The first day of summer arrived with the solstice on Sunday, June 20, 2021, at 11:32 p.m. EDT.
For those living in the Northern Hemisphere, Earth is tilting mostly toward the Sun. As seen from Earth, the Sun is directly overhead at noon 23.5 degrees north of the Equator, at an imaginary line encircling the globe, known as the Tropic of Cancer. It is named for the constellation “Cancer the Crab,” its northernmost point.
For those who live in the Southern Hemisphere, this is the shortest day of the year and the arrival of Winter. The solstice happens at the same moment for everyone, everywhere on Earth.
Why isn’t Summer on the same date every year? The timing of the summer solstice is not based on a specific calendar date or time. It depends on when the Sun reaches that northernmost point from the Equator. The summer solstice can occur anywhere from June 20-22.
The term “solstice” comes from the Latin words sol (sun) and sistere (to stand still.) At the solstice, the angle between the Sun’s rays and the plane of the Earth’s Equator (called declination) appears to stand still. This phenomenon is most noticeable at the Arctic Circle, where the Sun hugs the horizon for a continuous 24 hours, thus the term “Land of the Midnight Sun.”
Some people believe that our seasons are caused by the Earth’s changing distance from the Sun. In reality, it is due to the 23-degree tilt of the Earth’s axis, that the Sun appears above the horizon for different lengths of time at different seasons. The tilt determines whether the Sun’s rays strike at a low angle or more directly.
