On Monday, September 22, 2025, at 2:19 p.m. EDT, the sun will cross the celestial equator heading south, marking the autumn equinox in the Northern Hemisphere. That means shorter days and longer nights are on the way — but for sky-watchers, it also signals one of the best windows of the year to see the Northern Lights.
In fact, NOAA is forecasting a G1 geomagnetic storm on Sunday, September 21, with auroras potentially visible in 14 U.S. states.
Why the Equinox Matters for Auroras
The aurora borealis happens when charged solar particles funnel down Earth’s magnetic field lines and collide with gases high in the atmosphere, creating glowing sheets of green, red, and purple light.
But during the March and September equinoxes, geomagnetic disturbances are more likely thanks to something called the equinox effect. With Earth’s axis tilted sideways relative to the sun, the planet’s magnetic poles line up in such a way that solar wind particles can more easily slip into the magnetosphere.
In other words, the door to Earth’s skies is cracked open wider — giving auroras more opportunities to shine.
The Russell-McPherron Effect
Back in the 1970s, scientists Russell and McPherron explained this seasonal boost. The Russell-McPherron effect shows how Earth’s tilt at equinox makes its magnetic field more likely to reconnect with the sun’s field. When reconnection happens, solar wind streams pour into Earth’s magnetosphere, fueling brighter auroral displays.
It doesn’t guarantee auroras everywhere, but it raises the odds significantly — especially when paired with longer nights and the current solar maximum cycle, which peaks in 2025–2026.
Where and When to See the Northern Lights
- Date: Sunday night, September 21, 2025
- Forecast: G1-class geomagnetic storm
- Viewline: NOAA projects auroras could be visible across 14 northern U.S. states, stretching farther south than usual.
- Best viewing: Dark skies away from city lights, after local sunset until the early morning hours.
Keep an eye on the NOAA Space Weather Prediction Center’s aurora forecasts for real-time updates: NOAA SWPC Aurora 30-Min Forecast.
The Equinox Explained
The word equinox comes from the Latin for “equal night.” It’s the moment when day and night are nearly the same length across the globe. That’s because Earth’s axis — tilted at 23.4° — is aligned side-on to the sun. In June, the Northern Hemisphere leans toward the sun (longer, hotter days); in December, it leans away (shorter, colder days). The September equinox is the transition into astronomical fall in the Northern Hemisphere, and spring for the Southern Hemisphere.
Why September Is Prime Time
- Earth’s magnetic field is perfectly aligned for reconnection.
- Nights are getting longer, giving more hours of darkness to spot auroras.
- The sun is at solar maximum, boosting the chances of strong solar storms.
Together, these factors make September one of the top months worldwide for Northern Lights sightings.
FAQs:
When is the 2025 fall equinox?
Monday, September 22, 2025, at 2:19 p.m. EDT.
Why are auroras more likely at equinox?
Because of the Russell-McPherron effect — Earth’s tilt allows solar wind to interact more easily with the magnetosphere.
3. Where in the U.S. will auroras be visible on Sept. 21, 2025?
Up to 14 states, mainly in the northern tier, depending on local conditions and cloud cover.
