The science

How the aurora works, and the space science behind the forecast.

• What is the aurora?Light given off high in the atmosphere when particles guided in by Earth's magnetic field strike oxygen and nitrogen.
• From the Sun to the skyHow the solar wind, Earth's magnetic field and the auroral oval connect a storm on the Sun to the light above you.
• Aurora coloursGreen and red come from oxygen at different heights, blue and purple from nitrogen, and cameras see more colour than eyes.
• What drives a geomagnetic stormCoronal mass ejections, fast wind from coronal holes and substorms, and how long each takes to reach us.
• Reading the numbersKp and the G scale, Bz, solar wind speed and density, and hemispheric power, and what values matter for aurora.
• Where the data comes fromThe spacecraft, observatories and models behind every number in Polar Lights.
• Magnetic latitudeWhy some places see the aurora far more often than their position on a map suggests.
• The solar cycleThe Sun's roughly 11-year cycle, where Solar Cycle 25 is now, and what to expect over the next few years.
• The Sun's viewsWhat each of the 21 live views on the Sun tab shows, and what to look for in it.
• Rare sightsSTEVE, red SAR arcs, pulsating aurora and the southern lights.
• Photographing the auroraStarting settings for a camera and for a phone, and why photos show more than your eyes.
• The limits of forecastingWhat can be predicted, how far ahead, and why aurora forecasts are sometimes wrong.
• Glossary and sourcesShort definitions of the terms used in Polar Lights, with links to the agencies behind the data.