Glossary and sources
Short definitions of the terms used in Polar Lights, with links to the agencies behind the data.
Terms
- Active region: an area of strong magnetic field on the Sun, usually with sunspots, where flares and CMEs start.
- Aurora borealis / australis: the northern and southern lights.
- Auroral oval: the ring around each magnetic pole where aurora is most frequent.
- Bz: the north–south part of the solar wind's magnetic field. Negative (south) lets energy into Earth's field.
- CME (coronal mass ejection): a cloud of plasma and magnetic field thrown out from the Sun.
- Coronagraph: a telescope that blocks the Sun's disc to show the faint corona and CMEs.
- Coronal hole: a dark region in ultraviolet images where fast solar wind escapes.
- Flare: a sudden burst of light and X-rays from an active region, classed C, M or X, each ten times stronger than the last.
- G scale: NOAA's geomagnetic storm scale, G1 (Kp 5) to G5 (Kp 9).
- Halo CME: a CME seen spreading all round the Sun, heading towards Earth or directly away.
- Hemispheric power: the energy the aurora puts into one hemisphere's upper atmosphere, in gigawatts.
- IMF: the interplanetary magnetic field, the Sun's field carried by the solar wind.
- Kp: a 0 to 9 index of how disturbed Earth's magnetic field is over 3 hours.
- L1: the point about 1.5 million km towards the Sun where solar wind monitors sit.
- Magnetic latitude: latitude measured from Earth's magnetic poles, which decides how often you see aurora.
- Magnetosphere: the region of space controlled by Earth's magnetic field.
- nT (nanotesla): the unit for the solar wind's magnetic field.
- OVATION: NOAA's model of where aurora is likely in the next 30 to 90 minutes.
- S scale: NOAA's solar radiation storm scale, from high-energy protons.
- Shock: a sudden jump in solar wind speed and density, often the front of a CME.
- Solar wind: the stream of charged gas flowing out from the Sun.
- Substorm: a sudden release of stored energy that makes the aurora brighten and move.
- Sunspot number: the standard measure of solar activity.