Spring has officially sprung here in the Northern Hemisphere, while autumn has begun in the Southern Hemisphere! The vernal equinox—the start of astronomical spring—occurred today, March 20, 2025, at 5:01 a.m. EDT, and NOAA satellites had a perfect view.
The seasons change at various times of the year due to the planet’s axial tilt of 23.5 degrees as it orbits the sun. This tilt means the two hemispheres are exposed to different angles of sunlight, which result in variable lengths of daylight throughout the year. Twice a year, during the equinoxes, Earth’s axis is tilted neither toward nor away from the sun, resulting in nearly equal amounts of daylight and darkness worldwide. In fact, the word “equinox” is derived from two Latin words: aequus (equal) and nox (night). The spring (vernal) equinox and fall (autumnal) equinox are the only times the sun rises due east and sets due west for nearly every location on Earth.
This beautiful imagery above, via NOAA’s GOES East (GOES-16) satellite, shows how the seasons changed over the last year. The animation was made by taking one daily image from the satellite, collected at the same time each day, (11:50 UTC) and looping them together.
Credit: NOAA SciJinks
NOAA’s geostationary satellites, GOES East and GOES West, have an amazing view of this seasonal change from their position 22,236 miles above the equator. Orbiting at the same speed as Earth rotates, they each maintain a constant watch over a specific region over time. This allows them to track the terminator, or the line dividing day and night, as it shifts throughout the year. During an equinox, this line runs straight from north to south over the equator, a striking visual marker of seasonal change.
However, the length of day and night isn’t exactly equal on an equinox. This is due to refraction, or a bending of the light's rays through the atmosphere, which causes the sun to appear slightly above the horizon when its actual position is below it. Additionally, the days become a little longer at higher latitudes farther from the equator, because it takes the sun longer to rise and set.
While astronomical spring began on March 20, meteorological spring began on March 1. Astronomical seasons are based on the position of the Earth in relation to the sun, while meteorological seasons are based on the annual temperature cycle and calendar. Meteorological seasons begin on the first day of the months that include the equinoxes and solstices.Thus, meteorological spring began on March 1 and will end on May 31. Astronomical spring will officially end, and astronomical summer will begin, on the summer solstice on Friday, June 20 at 10:41 p.m. EDT.
The GOES East geostationary satellite, also known as GOES-16, keeps watch over most of North America, including the contiguous United States and Mexico, as well as Central and South America, the Caribbean, and the Atlantic Ocean to the west coast of Africa. The satellite's high-resolution imagery provides optimal viewing of severe weather events, including thunderstorms, tropical storms, and hurricanes.