Guide · Planning a night or a trip
Why the equinoxes are good for the northern lights
Answer
What SWPC says about the equinoxes
"The best Seasons for aurora watching are around the spring and fall equinoxes."
SWPC attributes the pattern to subtleties in how the solar wind interacts with the magnetosphere near the equinoxes. The result, in its words, is a tendency toward larger geomagnetic storms and better auroras in those weeks. A tendency is not a schedule. Big storms can arrive in any month, and a quiet equinox is common.
SWPC's storm page names the key condition for any storm: sustained fast solar wind with a magnetic field pointing south, opposite Earth's own field, at the front of the magnetosphere. The equinox effect works on that coupling. It does not create storms from nothing.
"The solar wind conditions that are effective for creating geomagnetic storms are sustained (for several to many hours) periods of high-speed solar wind, and most importantly, a southward directed solar wind magnetic field (opposite the direction of Earth's field) at the dayside of the magnetosphere."
The next equinoxes and how fast the nights change
Glow computes equinox instants from the sun's apparent longitude using Meeus' low-accuracy method, tested within 15 minutes of published times. The tables list the next two equinoxes and civil night at each Glow place two weeks before, on the day and two weeks after.
| Place | March 6 | March 20 | April 3 | Change per day |
|---|---|---|---|---|
| Fairbanks | 11.5 h | 9.9 h | 8.2 h | -7.0 min |
| Anchorage | 11.5 h | 10.1 h | 8.7 h | -5.9 min |
| Seattle | 11.5 h | 10.7 h | 9.8 h | -3.5 min |
| Minneapolis | 11.5 h | 10.8 h | 10.0 h | -3.2 min |
| Duluth | 11.5 h | 10.7 h | 9.9 h | -3.4 min |
| Portland, Maine | 11.5 h | 10.8 h | 10.1 h | -3.0 min |
| Buffalo | 11.5 h | 10.8 h | 10.1 h | -3.0 min |
| Reykjavik | 11.5 h | 10.0 h | 8.3 h | -6.8 min |
| Tromsø | 11.5 h | 9.4 h | 7.2 h | -9.1 min |
| Yellowknife | 11.5 h | 10.1 h | 8.6 h | -6.3 min |
| Place | September 9 | September 23 | October 7 | Change per day |
|---|---|---|---|---|
| Fairbanks | 8.4 h | 10.1 h | 11.6 h | +6.9 min |
| Anchorage | 8.9 h | 10.3 h | 11.6 h | +5.8 min |
| Seattle | 10.0 h | 10.8 h | 11.6 h | +3.4 min |
| Minneapolis | 10.1 h | 10.8 h | 11.6 h | +3.1 min |
| Duluth | 10.0 h | 10.8 h | 11.6 h | +3.3 min |
| Portland, Maine | 10.1 h | 10.8 h | 11.5 h | +3.0 min |
| Buffalo | 10.2 h | 10.9 h | 11.5 h | +2.9 min |
| Reykjavik | 8.5 h | 10.1 h | 11.6 h | +6.7 min |
| Tromsø | 7.4 h | 9.6 h | 11.6 h | +8.9 min |
| Yellowknife | 8.8 h | 10.2 h | 11.6 h | +6.1 min |
Near the March equinox civil night shrinks every day; near September it grows. The change is largest at high latitude. SWPC flags this directly: the number of hours of darkness decreases rapidly near the spring equinox and increases rapidly near the fall one, so a trip planned for late March can lose dark hours quickly.
Why equinox nights are not 12 hours dark
At an equinox the sun crosses the celestial equator, so day and night are close to equal everywhere. Civil night is shorter than that, because twilight takes a share at both ends. At high latitude the sun sinks at a shallow angle and spends longer between 0 and -6 degrees, so the far-north towns lose more of the night to twilight. That is why Tromsø shows less civil night than Minneapolis on the same equinox date in the table above.
Spring or fall?
For a high-latitude trip, the two equinoxes are not equal. In late September, nights at Fairbanks, Yellowknife or Reykjavik are lengthening fast and the dark season is opening. In late March they are shortening fast toward the no-darkness weeks of summer. Tromsø's civil night on March 15 is 10.2 hours; by April 15 it is 4.8.
Lower latitudes feel the change less. Minneapolis moves from 11.0 hours of civil night on March 15 to 9.3 on April 15. At the same dates Fairbanks moves from 10.4 to 6.6.
Weather also differs by season and place; each town page gives NASA POWER's cloud average by month. For US towns, check NWS cloud as the date approaches. For every town, the aurora season finder shows the full-year pattern of darkness.
Using the equinox in a plan
- Pick the equinox that suits your destination's darkness: September for the far north if you want long nights that are still growing.
- Pair it with the moon. The moon planner shows which equinox-season nights are moon-free.
- Read the month pages, such as Fairbanks in September or Reykjavik in March, for night-by-night counts.
- Watch SWPC forecasts in the days before. Storm arrival is only known days or hours ahead, never weeks.
Treat the equinox as a small edge on top of the basics. Darkness, clear sky and a view to the north decide far more nights than the calendar does. A clear, dark night in January beats a cloudy one in March.
Questions
- Are the northern lights better at the equinox?
- SWPC says there is a tendency toward larger geomagnetic storms, and thus better auroras, near the spring and fall equinoxes. It is a tendency, not a guarantee.
- When is the next equinox?
- The tables on this page give the next two equinox instants in UTC, computed from the sun's apparent longitude.
- Is March or September better for northern lights?
- Both sit near an equinox. At high latitude September offers nights that are growing longer; March nights are shrinking toward summer, which SWPC flags as a caveat for travelers.
- How fast do nights shrink in March at Tromsø?
- Civil night at Tromsø falls from 10.2 hours on March 15 to 4.8 on April 15.
- Can big storms happen outside the equinox months?
- Yes. SWPC describes a tendency, not a rule. Storms follow solar wind conditions, which can line up in any month.
Sources and verification
- NOAA SWPC, Tips on viewing the aurorahttps://www.spaceweather.gov/content/tips-viewing-aurora
Quoted figures last checked against their sources on 2026-09-30; next review 2026-12-31. Computed figures come from SunCalc and the IGRF-14 dipole as described in the methodology. Every quote is listed in the sources ledger.