Northern lights guides
Answer
Each guide answers one question with NOAA SWPC's own wording and a table computed for the 10 Glow towns. Start with what causes the aurora and the Kp index, then move to forecasts and planning. Every figure is either quoted with its source and check date or computed from SunCalc and the IGRF-14 dipole.
16
guides
How the aurora works
What makes the light, where it sits and when the sky is dark enough.
- What causes the northern lights?Electrons from the magnetosphere strike oxygen and nitrogen 80 to 500 km up and give off light. How that makes two ovals, and which towns sit under them.
- What is the Kp index?Kp runs from 0 to 9 and rates 3-hour magnetic disturbance from 13 observatories. What each step means for the aurora and the oval's edge.
- Geomagnetic latitude, explained for aurora watchersThe aurora follows geomagnetic latitude, not the map. How the IGRF-14 dipole shifts 10 aurora towns by up to 9 degrees, and why Minneapolis beats Seattle.
- How dark does it need to be to see the aurora?Civil, nautical and astronomical twilight end at -6, -12 and -18 degrees of sun. Which one Glow counts as dark, and night length for 10 aurora towns.
- How far away can you see the northern lights?SWPC says bright aurora can be seen from up to 1000 km away. The geometry behind that figure, and how far 10 aurora towns sit from the oval's edge.
Reading forecasts
Kp, OVATION, NOAA alerts and NWS cloud, and what each one can tell you.
- How to read the NOAA aurora forecastNOAA's OVATION map gives an aurora value per 1 degree cell, 30 to 90 minutes ahead. What the percent means, which cell is yours and when to distrust it.
- Kp to latitude chart for the northern lightsThe SWPC rule puts the oval's edge at 66 degrees geomagnetic at Kp 0, then 2 degrees lower per step. The Kp each of 10 aurora towns needs, in one table.
- How much warning do aurora forecasts give?Days for a coronal mass ejection, 30 to 90 minutes for the OVATION map, none on Kp fallback. What each lead time rests on, from NOAA SWPC's own pages.
- Geomagnetic watches, warnings and alerts explainedNOAA SWPC ties watches to Kp 5 and up, warnings and alerts to Kp 4 and up. What each product means for aurora, and which of 10 towns each level reaches.
- Cloud cover and the auroraOvercast hides any aurora. How NWS sky cover percent maps to its octant terms, what Glow shows for US towns, and the long-term average elsewhere.
Planning a night or a trip
Time of night, moon, season and the lower 48, with numbers for 10 towns.
- What time of night is best for the northern lights?SWPC says 10 PM to 2 AM local time. Why the window centers on midnight, how daylight saving and time zones shift it, and solar midnight for 10 towns.
- The best month to see the northern lightsDark hours for 10 aurora towns in every month, with SWPC's equinox advice. Why September and March lead in the far north, and winter in the lower 48.
- Why the equinoxes are good for the northern lightsSWPC says larger storms tend to cluster near the spring and fall equinoxes. The next equinox dates, and how fast darkness changes then at 10 aurora towns.
- Northern lights and the full moonA full moon dims how bright the aurora looks, not how bright it is. Moon-free dark hours on the next new and full moon for 10 aurora towns.
- When is it too light for the northern lights?Midnight sun and white nights hide the aurora. The dates with no civil darkness, and the dark season, for Fairbanks, Tromsø, Reykjavik and 7 more towns.
- Seeing the northern lights from the lower 48 statesDuluth, Minneapolis, Seattle, Buffalo and Portland, Maine sit 52 to 56 degrees geomagnetic. The Kp and NOAA storm level each needs, from SWPC's own rules.