Glossary of Acronyms and Technical Terms

How to speak Scientish

For those of you that want to follow along in the blog, but find that the authors frequently use jargon and acronyms (sorry!), here is a glossary of terms we use constantly when talking about sunspots, image processing methods, and the Sun in general. If you would like more terms described, please let us know in the comments section and we will attempt to define them- though realise that often each research group, or even each scientist may have a different definition of a term!


AR – Active Region

NLFF – Non-linear Force Free

PFSS – Potential Field Source Surface

PSL – Polarity Separation Line

NL – Neutral line

SEP – Solar Energetic Particle

SS – sunspot

SSG – sunspot group


Active Region – a magnetic structure on the Sun that is active (dynamic in some way). The region may include one or more sunspot, magnetic loops, and filaments. They may produce flares and coronal mass ejections.

Alpha – a Hale classification; a sunspot group with only one polarity (will appear all white or all black in a magnetogram).

Beta – a Hale classification; a sunspot group with two polarities, configured so a relatively straight line can be drawn between them (tends to appear roughly equal parts white and black in a magnetogram).

Cosmic Ray – energetic particles originating from sources outside of the solar system that travel close to the speed of light. Supernovae are thought to be a source of many cosmic rays. When cosmic rays intersect imager CCDs, they are often observed as bright streaks.

Delta – a Hale classification; a sunspot group with a spot showing both polarities within the same surrounding penumbra. (example)

Feature – an AR, SSG, SSG complex, flux fragment. In other words: a thing we are observing on the Sun.

Gamma – a Hale classification; a sunspot group with ‘mixed’ polarities; it will not be possible to draw a straight line separating the two polarities.

Hale Classification – a scheme for classifying (grouping) sunspot groups into ‘types’. The scheme was invented aaround 1919 by George Ellery Hale (paper). Both magnetograms and visible light images are required to make a Hale classification. The scheme includes the classifications: alpha (usually decayed SSGs), beta (most common), gamma (rare), beta-gamma, beta-delta, beta-gamma-delta (tends to be the most flare active).

Solar Energetic Particle (SEP) – particles that often reach speeds near the speed of light and that can be accelerated in solar flares as well as at CME shock fronts. When SEPs intersect imager CCD cameras, they are usually observed as bright streaks.

Sunspot Group (SSG) – a collection of more than one sunspot in close proximity.

Sunspot Group Complex – or simply a ‘complex’ or ‘AR complex’, is a conglomeration of 2 or more bipolar features in close proximity.

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