Glossary of Terms

Active Region (AR) is a localized, transient volume of the solar atmosphere in which plages, sunspots, faculae, flares, etc. may be observed.

Disk is the visible surface of the Sun (or any heavenly body) projected against the sky.

Flare is a sudden eruption of energy on the solar disk lasting minutes to hours, from which radiation and particles are emitted.

HMI is an instrument designed to study oscillations and the magnetic field at the solar surface, or photosphere. HMI is on the three instruments on the Solar Dynamics Observatory. HMI, which stands for Helioseismic and Magnetic Imager is a successor to the Michelson Doppler Imager (MDI). The source of HMI data is the Joint Science Operations Center (JSOC).

A magnetogram is not an image of the Sun which you might see with your eyes. It is an image taken by an instrument which can detect the strength and location of the magnetic fields on the Sun. In these line-of-sight magnetograms, the white areas are regions of strong "north" magnetic polarity (directed towards the observer), and the dark areas are regions of strong "south" magnetic polarity (directed away from the observer). The gray areas are weak field areas.

NOAA - The National Oceanic and Atmospheric Administration is a federal agency focused on the condition of the oceans and atmosphere. Active regions or Sunspot numbers are available from the NOAA National Geophysical Data Center.

Plage is an extended emission feature of an active region that exists from the emergence of the first magnetic flux until the widely scattered remnant magnetic fields merge with the background.

Solar Cycle is the approximately 11-year quasi-periodic variation in frequency or number of solar active events.

Solar particle events (SPEs) are injections of energetic electrons, protons, alpha particles, and heavier particles into interplanetary space. These particles are accelerated to near relativistic speeds by the interplanetary shock waves which precede fast coronal mass ejections and which exist in the vicinity of solar flare sites. The most energetic particles arrice at Earth within tens of minutes of the event on the Sun, while the lower-energy population arrices over the course of a day.

Coronal mass ejections (CMEs) are huge bubbles of plasma (ionized atomic matter with high kinetic energy) threaded with magnetic field lines that are ejected from the Sun's corona (outer atmosphere).