Satellite: GOES-19 (GOES East)
Product: GeoColor
Instrument: Advanced Baseline Imager
Timespan: Sept. 21, 2024 (11:50 UTC) – Sept. 22, 2025 (11:50 UTC)
Fall has officially begun in the Northern Hemisphere, while those in the Southern Hemisphere are experiencing the start of spring. NOAA’s GOES East (GOES-19) satellite viewed the autumnal equinox, which marked the official start of astronomical fall, on Monday, Sept. 22, 2025, at 2:19 p.m. EDT.
The seasons change at different times of the year due to the Earth’s 23.5-degree axial tilt. As Earth orbits the sun, this tilt causes the hemispheres to receive varying angles of sunlight throughout the year, which leads to differing amounts of daylight.
An equinox takes place two times a year, in the spring (vernal) and fall (autumnal), when Earth’s axis is neither tilted toward nor away from the sun. This positioning results in nearly equal hours of daylight and darkness across the globe. The term “equinox” comes from the Latin words aequus (equal) and nox (night). At the equator, the sun sits directly overhead at noon during both equinoxes. It also rises due east and sets due west for nearly every location on Earth— something that doesn’t happen at any other time of year.
Technically though, day and night aren’t perfectly equal on the equinox. As sunlight passes through Earth’s atmosphere, it actually bends somewhat. Thus, when the sun is below the horizon, it can still appear above it. This refraction, along with the slower sunrise and sunset at higher latitudes, makes the day appear slightly longer than the night during an equinox.
While astronomical fall began on Sept. 22, meteorological fall started several weeks earlier, on Sept. 1. Unlike astronomical seasons, which are tied to Earth’s position relative to the sun, meteorological seasons are based on the annual temperature cycle. Meteorological fall runs from Sept. 1 through Nov. 30, while astronomical fall will continue until the winter solstice on Sunday, Dec. 21, at 10:03 a.m. EST.
NOAA’s GOES-18 and GOES-19 satellites, orbiting 22,236 miles above the equator, keep a continuous watch over the Western Hemisphere as the planet rotates. This perspective allows them to track the “terminator,” or the dividing line between day and night. The angle of the terminator changes with the seasons, and during the equinox, it appears as a straight north-south line directly over the equator. NOAA satellites capture this clear signal of the change in season every year.