The 2025 autumnal equinox arrived on September 22, marking the start of astronomical fall in the Northern Hemisphere. At the planet’s high latitudes, however, signs of the changing seasons were already apparent.
On September 18, the OLI (Operational Land Imager) on Landsat 8 acquired this image of yellow-tinged hills above the Tanana River near the town of Delta Junction, Alaska (out of frame to the west). In this subarctic region of Interior Alaska, fall-like conditions are fleeting, wedged between short, mild summers and long, frigid winters.
The area’s plant life flourishes in the months around the summer solstice in June, when daylight is plentiful. From May to July, there is no night—only twilight and daylight—at this latitude. Scrubby forests with stunted trees like black spruce, American dwarf birch, and quaking aspen cover the hillsides, while sedges, mosses, and shrubs such as lingonberry and bog blueberry grow in soggier low-lying areas. Farmers utilize the short growing season to cultivate cereal grains, grasses for forage and seed, and hardy legumes and vegetables.
While the seasons bring stark transformations, wildland fire leaves its own lasting mark on the land. The dark brown burned areas visible southeast of Healy Lake are likely the result of the Twelvemile Lake and Sand Lake fires, which swept through stands of black spruce and brush earlier in the summer. Black spruce, an evergreen species, is especially fire-prone.
The brilliant colors of autumn peak when air temperatures drop and waning daylight causes plants to slow and stop the production of chlorophyll—the molecule that plants use to synthesize food. Without chlorophyll, the green pigment fades, revealing various yellow and red pigments. The change in colors, well underway at the time of the equinox in the far north, will progress southward as the season goes on, with peak color showing up as late as mid-November in more temperate regions.
Likewise, the Sun will continue inching south in the sky. On the September equinox, the Sun crossed the plane of our planet’s equator. (Someone standing at the equator would see the Sun directly overhead at noon that day.) Observers everywhere on Earth will notice the Sun cross the sky farther south each day until the December solstice, when it will begin its steady march back north.
References & Resources
- Alaska Department of Fish and Game Boreal Forest in Alaska. Accessed September 22, 2025.
- Alaska Highway - Delta Junction, Alaska Farming. Accessed September 22, 2025.
- NASA (2025, March 14) Embracing the Equinox. Accessed September 22, 2025.
- NASA Earth Observatory (2011, September 23) Seeing Equinoxes and Solstices from Space. Accessed September 22, 2025.
- National Ecological Observatory Network Delta Junction NEON / DEJU. Accessed September 22, 2025.
NASA Earth Observatory image by Michala Garrison, using Landsat data from the U.S. Geological Survey . Story by Lindsey Doermann .
