The Kp index sets how far south the aurora reaches: Kp 5 brings it to the northern US
The Kp index measures how disturbed Earth's magnetic field is, on a scale from 0 to 9, every three hours. NOAA's Space Weather Prediction Center turns Kp 5 and above into geomagnetic storm levels on its G scale, from G1, minor, to G5, extreme. The higher the Kp, the farther the auroral oval, the ring of aurora around the magnetic pole, spreads toward the equator.
| Kp | Storm | Level | Aurora low in the north as far south as about |
|---|---|---|---|
| 3 or less | none | Quiet | Alaska, northern Canada, Scandinavia, Iceland |
| 5 | G1 | Minor | The northern edge of the US: northern Maine, Michigan, Minnesota, North Dakota, Montana, Washington |
| 7 | G3 | Strong | Pennsylvania, Illinois, Iowa, Nebraska, Wyoming, northern California |
| 9 | G5 | Extreme | Rare: the southern US, as far as Texas and Florida; the May 2024 storm reached Mexico |
Kp 6, G2, and Kp 8, G4, fall between the rows. The lines are approximate: they follow magnetic latitude, which runs farther south in eastern North America than in the west, and an aurora low on the northern horizon is often seen a few hundred kilometers south of them.
The Sun passed solar maximum in October 2024, but big storms come in the declining years too
The Sun's activity rises and falls over about 11 years. Solar Cycle 25 began in December 2019 and peaked, by NASA's count of sunspots, in October 2024; the May 2024 storm, the strongest in more than 20 years, showed the aurora across most of the United States. Activity is now declining toward a minimum around 2030.
The declining phase still brings storms. Some of the strongest flares and storms of past cycles came years after maximum, and in the declining years long-lived coronal holes send fast streams of solar wind past Earth once every 27 days as the Sun turns, so active periods repeat. Severe storms in November 2025 and January 2026 showed the aurora as far south as Belgium.
Look north, away from city lights, in the hours around local midnight
- Time of night: the oval is closest to you around local midnight, from about 10 pm to 2 am, but a storm can light up any time it is dark.
- Time of year: the weeks around the March and September equinoxes see more storms, because Earth's magnetic field lines up best with the solar wind's then. Long winter nights give more dark hours; the bright summer nights of Alaska and Scandinavia hide the aurora entirely.
- Direction: from the US, look north. A view down to the northern horizon matters more than a perfect dark sky; in a big storm the aurora climbs overhead and even fills the southern sky.
- The Moon: a bright Moon washes out a faint display but not a strong one.
A storm overhead in Canada shows low in the north from 1,121 km away
The aurora glows high in the atmosphere: the common green light from oxygen at 100 to 200 km, the rarer red light from oxygen at 200 to 400 km, and purple and pink fringes from nitrogen at the lower edge. That height is why it is seen so far away. Green aurora at 100 km sits on the horizon from 1,121 km away, and the red tops at 400 km from 2,201 km away, which is why observers far south of a storm often see only a red glow low in the north.
A phone camera sees colors the eye cannot
Faint aurora looks gray or white to the eye, because the eye's color receptors do not work in dim light. A camera collects light for seconds and records the green and red. Many people now find the aurora by taking a photo of a gray glow in the north. Use night mode on a phone, or on a camera a wide lens, ISO 1600 to 3200 and exposures of 2 to 10 seconds; shorter exposures keep the curtains sharp in a fast-moving display.
The southern lights, aurora australis, are seen from Tasmania, New Zealand and Patagonia
The same storms light an oval around the south magnetic pole. From Tasmania and the South Island of New Zealand the aurora australis is seen low in the south several times a year, and in big storms from mainland Australia, southern Chile and Argentina, and South Africa.
Aurora forecasts look ahead three days, but the 30-minute map is what counts
A coronal mass ejection, the eruption that drives the biggest storms, takes one to three days to reach Earth, so storms are forecast a day or two ahead, but how strong a storm gets depends on the direction of its magnetic field, which is measured only about an hour before it arrives, by spacecraft at the L1 point 1.5 million km toward the Sun. NOAA's free tools:
- Aurora dashboard: the current Kp, the 3-day forecast and alerts.
- 30-minute forecast: the OVATION map of where the oval is now.
- Tonight's view line: how far south it may be seen low on the horizon.
Sign up for alerts, watch the 30-minute map once it is dark, and go outside to look: forecasts miss storms both ways. Find a dark site with a low northern horizon.