Glossary

Aurora and Kp Index

An aurora is a coloured glow in the night sky. It appears when particles from the Sun are guided by the Earth's magnetic field towards the poles and excite gases in the upper atmosphere. Oxygen gives green and red, nitrogen blue and purple.

The Kp index measures magnetic disturbance from 0 to 9. From 5 upwards it is called a geomagnetic storm, and auroras become visible much further from the poles, sometimes as far south as France. The map shows the area where an aurora is likely.

Other Definitions

• Tectonic Plate
• Subduction
• Mid-Ocean Ridge
• Transform Fault
• Fault
• Earthquake, Epicentre and Hypocentre
• Magnitude
• Intensity (Mercalli Scale)
• Aftershock
• Tsunami
• Active Volcano
• Stratovolcano
• Shield Volcano
• Caldera
• Volcanic Explosivity Index (VEI)
• Pyroclastic Flow
• Lahar
• Hotspot
• Tropical Cyclone, Hurricane, Typhoon
• Saffir-Simpson Scale