Space weather

Auroras and space weather

The northern lights are technically weather — of a different atmosphere. Here is how space weather works, and how to see it.

The mechanism

Solar activity ejects charged particles into space.
Some travel toward Earth (solar wind).
Earth's magnetic field deflects most.
Some funnel down along magnetic field lines at poles.
Charged particles collide with oxygen and nitrogen in atmosphere.
Atoms glow when energized then relax.
Different atmospheric gases + altitudes produce different colors.

The colors

Green

Oxygen at 60-100 mi altitude. Most common color.

Red

Oxygen at 100-200 mi. Rare, high-altitude glow.

Purple/blue

Nitrogen at various altitudes.

Pink

Mix of red and green boundary.

White

Very intense aurora with all colors.

Yellow

Rare atmospheric mix.

The forms

Arc

Simple curved band across sky. Most common.

Corona

Sky-wide rays radiating from magnetic zenith.

Curtain

Rippling curtain of light.

Rays

Vertical shafts of light.

Spirals

Rare rotating structures.

Steve

Recently identified purple ribbon. Not classical aurora but related.

Solar cycle

Sun activity follows 11-year cycles.
Solar minimum: few auroras.
Solar maximum: frequent auroras.
Current cycle: 25, peak 2024-2026.
Cycle 26 predicted to start 2030-2032.
Historical maximum in 1859 (Carrington Event).
Recent peak 2013-2014.

Space weather forecasting

NOAA Space Weather Prediction Center (SWPC) monitors.
GOES satellite X-ray detectors: 24/7.
SOHO / SDO satellites image the sun.
DSCOVR at Lagrange 1: sees solar wind before it hits Earth.
Advance warning: 30-90 minutes for major CMEs.
Long-range forecasts based on active regions on visible solar disk.
Free forecasts at swpc.noaa.gov.

The Kp index

The primary geomagnetic activity indicator.

Scale: 0-9.
0-2: quiet. Auroras not visible from mid-latitudes.
3-4: moderate. Auroras visible from northern US border.
5-6: minor storm. Auroras from northern half of US.
7-8: strong storm. Auroras from Central US.
9: extreme storm. Auroras from Southern US, sometimes tropics.
Updated every 3 hours.

Where to see auroras

Fairbanks Alaska

Aurora capital of the US. 200+ nights per year.

Yellowknife Canada

Aurora capital of the world (per some rankings).

Iceland

European aurora tourism destination.

Northern Norway (Tromsø)

European destination.

Finnish Lapland

Aurora + Santa combined.

Northern Minnesota / Wisconsin / Michigan

US aurora belt in strong storms.

Wyoming / Montana Plains

Dark skies + clearer aurora.

Northern Maine / New Hampshire / Vermont

Occasionally strong aurora.

The famous auroras

1859 Carrington Event — auroras seen from Caribbean. Telegraph lines electrified.
1989 Quebec blackout — geomagnetic storm knocked out power grid.
2003 Halloween storms — auroras from Texas.
2011 St. Patrick's Day storm — visible from mid-latitudes.
2015 St. Patrick's Day storm — visible from US-Mexico border.
2024 May Mother's Day storm — auroras from Florida.
2024 October storm — X-class flare event.

Photography tips

Full frame camera preferred.
Fast wide lens (14-24mm f/2.8).
ISO 1600-6400.
Aperture wide open.
Shutter 3-15 seconds.
Sturdy tripod.
Manual focus at infinity (turn slightly back from stop).
Turn off image stabilization.
Shoot RAW.
Multiple exposures for star trails.
Include foreground element for scale.

The Carrington scenario

The 1859 Carrington Event was the strongest known geomagnetic storm.

Would cost $1-2 trillion if repeated today.
Would knock out multiple power grids for months.
Would damage most satellites in orbit.
GPS unusable for weeks.
Some 100-year statistical estimates suggest 10-12% chance per decade.
Utilities have begun hardening infrastructure.
Not a matter of if, but when.

Space weather impacts (beyond auroras)

Airline routing (rerouted from polar routes during storms).
GPS accuracy degraded.
Radio blackouts on HF frequencies.
Satellite drag increased.
Power grid instability.
Pipeline current effects.
Astronaut radiation exposure.
Some biological impacts documented.