At exactly 2:19 p.m. EDT on Monday, September 22, 2025, the sun will cross the celestial equator heading south. That marks the fall equinox in the Northern Hemisphere — the first day of autumn.
With longer nights on the horizon, it also kicks off one of the best times of the year to witness the aurora borealis. Thanks to a unique mix of Earth’s tilt and solar activity, this time of year opens the door to more frequent and intense geomagnetic storms — and that means more dazzling Northern Lights.
Table of Contents
Equinox
Let’s start with the basics. The word equinox comes from the Latin for “equal night.” That’s because, on this day, most places on Earth experience almost equal amounts of daylight and darkness. Why? Because Earth’s axis is tilted at 23.4 degrees, but during an equinox, it points neither toward nor away from the sun.
In the Northern Hemisphere, this marks the beginning of astronomical fall. In the Southern Hemisphere, it signals the start of spring. But for sky-watchers, it’s not just about the seasons — it’s about how our planet aligns with the sun and what that does to our magnetic field.
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Auroras
The Northern Lights, or aurora borealis, are one of nature’s most stunning phenomena. They appear when solar wind — made of charged particles from the sun — slams into Earth’s atmosphere. When these particles hit oxygen and nitrogen high above us, they produce glowing waves of light, usually green, sometimes red or purple.
These auroras are always dancing near Earth’s poles, but they become more visible and active when our magnetic defenses let more of that solar energy in. And around the fall equinox, that’s exactly what happens.
Geometry
Here’s where the equinox really gets interesting. During this time, Earth’s axis is side-on to the sun. This creates better alignment between Earth’s magnetic field and the direction of the solar wind.
It’s like Earth’s magnetic door is slightly ajar. Solar particles have an easier time slipping through “cracks” in our magnetosphere. The result? More geomagnetic disturbances — and brighter, more widespread auroras. This seasonal spike is often called the “equinox effect.”
Forecast
The National Oceanic and Atmospheric Administration (NOAA) is already forecasting a G1-rated geomagnetic storm for Sunday, September 21. That’s a minor solar storm, but it’s still strong enough to produce visible auroras in parts of the U.S.
If the skies are clear, people in up to 14 states — including Montana, Wisconsin, Minnesota, North Dakota, and even parts of Illinois — might catch the light show. With the equinox arriving the very next day, we could be in for an aurora-packed weekend.
Here’s a quick summary of what to expect:
| Date | Storm Rating | Visibility Range |
|---|---|---|
| Sept 21 | G1 (Minor) | 14 U.S. states, mainly North |
| Sept 22 | G1 Possible | Post-equinox aurora chance |
| Sept 23-25 | G1-G2 Range | Monitor NOAA updates |
Russell-McPherron
This isn’t just a coincidence. Scientists call the phenomenon behind this spike in activity the Russell-McPherron effect. First proposed in the 1970s, this theory explains how Earth’s tilt during equinoxes improves the connection between Earth’s and the sun’s magnetic fields.
When that connection happens, the solar wind flows more easily into our magnetosphere. That leads to more geomagnetic storms and, you guessed it — more auroras. It doesn’t mean the Northern Lights are guaranteed, but it does mean we’re playing with better odds.
Timing
So, when should you be watching the skies? The best window is typically within a week or two of the equinox. The combination of longer nights, stronger solar activity, and Earth’s perfect magnetic angle makes this time of year a prime viewing season.
And don’t forget — the sun is approaching its peak in the 11-year solar cycle, which means stronger solar flares are more common. That just adds fuel to the aurora fire.
Want to catch a glimpse? Check NOAA’s aurora forecasts regularly, find a dark spot away from city lights, and stay up late or wake up early. If the solar weather cooperates, you might just see green and red curtains dancing across the sky.
There’s something magical about the skies around the fall equinox — and this year, they might just put on one of their best shows yet.
FAQs
What causes the Northern Lights?
Charged solar particles hitting Earth’s atmosphere.
What is the equinox effect?
A seasonal spike in geomagnetic activity due to Earth’s tilt.
When is the fall equinox in 2025?
It’s on Monday, September 22 at 2:19 p.m. EDT.
What is a G1 geomagnetic storm?
A minor solar storm that can trigger visible auroras.
Can auroras be seen in the U.S.?
Yes, especially in northern states during storms.
