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Astronomy

Key Terms

AstronomyKey Terms
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
(of the Sun) 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; granulation is produced by upwelling currents of gas that are slightly hotter, and therefore brighter, than the surrounding regions, which are flowing downward into the Sun
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
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