NOAA Satellites Watch the Winter Solstice Approach

The official start of astronomical winter, marked by the winter solstice, will occur this Sunday, Dec. 21, 2025, at 10:03 a.m. EST. This moment marks the shortest day and longest night of the year in the Northern Hemisphere, where the Earth reaches its maximum tilt away from the sun. At the solstice, the sun appears directly over the Tropic of Capricorn, 23.5 degrees south of the equator.

NOAA’s satellites allow us to see how Earth’s tilt drives changes in sunlight and seasons. The loop above was created using one image per day from NOAA’s GOES East satellite over the past year. It includes imagery from GOES-16 and GOES-19, which became the new operational GOES East satellite in April 2025. Each of these images were taken at the same time (11:50 UTC) every day and looped together.

The satellite images reveal the terminator, or the shadow line that divides day and night, cutting a sharp angle across Earth. During this event, the North Pole is shrouded in 24-hour darkness, while the South Pole experiences 24-hour daylight– a contrast that flips in June during the summer solstice.

Astronomical winter in the Northern Hemisphere is defined by Earth’s position relative to the sun. This differs from meteorological winter, which is based on the annual temperature cycle as well as our calendar, and starts on Dec. 1.