Video of Earth Transitioning From Winter Released to Mark Summer Solstice 2021

Summer has started in the Northern Hemisphere, and satellite imagery of the Earth's transition between the seasons has been released.

On Sunday, the U.S. National Oceanic and Atmospheric Administration (NOAA) released a video to Facebook showing how the Earth's tilt causes us to experience the seasons.

The video, above, was created using images from NOAA's Geostationary Operational Environmental Satellite, or GOES, which captured a snapshot of Earth every day between December 21, 2020 and June 18, 2021.

Edited together into a video, the photos show how the border between night and day shifts along the planet, and how its angle changes as the year progresses.

NOAA said the footage "shows the change from winter to summer due to the Earth's tilt." A color version, seen below, was released to Twitter.

#SATELLITE SPOTLIGHT: Astronomical #summer arrives in the Northern Hemisphere at 11:32 pm EDT today! Notice how the sun's angle changes in our part of the world from winter to summer in this @NOAA #GOES16🛰️ GeoColor time lapse from December 2020 to June 2021. #SummerSolstice

— NOAA Satellites - Public Affairs (@NOAASatellitePA) June 20, 2021

The Earth is tilted on its axis of rotation at an angle of about 23.5 degrees as it orbits the sun. This angle means that, for one half of the year, the Northern Hemisphere is tilted towards the sun and the Southern Hemisphere tilted away, and vice versa.

It is summer in the Northern Hemisphere when that half of the planet is tilted towards the sun. When this tilt is most pronounced, it is called the summer solstice. It marks the beginning of the astronomical summer, according to NASA.

The summer solstice also marks the longest days of the year, between June 20 and June 22. At the same time, the Southern Hemisphere is experiencing its shortest days of the year as it goes through its winter solstice.

Historically, the solstices have had cultural significance around the world. For Greeks, the summer solstice marked a month-long countdown to the Olympics and was also the start of a festival to honor the god Cronus, the patron of agriculture, according to Scientific American.

On Monday morning, people flocked to the site of Stonehenge, a prehistoric stone monument in the U.K. While researchers are still probing the purpose of the several thousand-year-old structure, it is linked to the solstices because when one stands at a certain point within the monument on the summer solstice, the sun rises over the Heel Stone—a rock that lies outside the main circle. This causes a shadow to be cast towards the rest of the formation.

Today, druids still come to Stonehenge to perform rituals on the summer solstice. According to the BBC, about 100 people turned up to the site on Monday morning and a live feed of the solstice at Stonehenge was cut off, with the hosting English Heritage group saying many people disregarded advice not to travel to the site.

Superintendent Dave Minty, from Wiltshire Police, told the BBC that "everything has been peaceful" but "the numbers have caused us some issues."

Earth from space
A photo of the boundary between night and day, taken by astronaut Christina Hammock Koch aboard the International Space Station, 2019. The summer solstice marks the longest days of the year. NASA / Christina Hammock Koch