The sun: a garden variety star

active region

An area on the Sun where magnetic fields are concentrated; sunspots, prominences, flares, and CMEs all tend to occur in active regions.

aurora

Light radiated by atoms and ions in the ionosphere excited by charged particles from the Sun, mostly seen in the magnetic polar regions.

chromosphere

The part of the solar atmosphere that lies immediately above the photospheric layers.

corona

The outer (hot) atmosphere of the Sun.

coronal hole

A region in the Sun’s outer atmosphere that appears darker because there is less hot gas there.

coronal mass ejection (CME)

A solar flare in which immense quantities of coronal material—mainly protons and electrons—is ejected at high speeds (500–1000 kilometers per second) into interplanetary space.

differential rotation

The phenomenon that occurs when different parts of a rotating object rotate at different rates at different latitudes.

granulation

The rice-grain-like structure of the solar photosphere, produced by upwelling currents of gas that are slightly hotter and therefore brighter than the surrounding regions.

Maunder Minimum

A period during the seventeenth century when the number of sunspots seen throughout the solar cycle was unusually low.

photosphere

The region of the solar (or stellar) atmosphere from which continuous radiation escapes into space.

plage

A bright region of the solar surface observed in the light of some spectral line.

plasma

A hot ionized gas.

prominence

A large, bright, gaseous feature that appears above the surface of the Sun and extends into the corona.

solar flare

A sudden and temporary outburst of electromagnetic radiation from an extended region of the Sun’s surface.

solar wind

A flow of hot, charged particles leaving the Sun.

sunspot

Large, dark features seen on the surface of the Sun caused by increased magnetic activity.

sunspot cycle

The semiregular 11-year period with which the frequency of sunspots fluctuates.

transition region

The region in the Sun’s atmosphere where the temperature rises very rapidly from the relatively low temperatures that characterize the chromosphere to the high temperatures of the corona.