10.6 Key Terms

Active region: A place on the Sun where a sunspots, flares, and bright regions in the chromosphere and corona are seen. 10.4

Aurora: charged particles accelerated by the solar wind  that can follow Earth’s magnetic field down into our atmosphere; these particles strike molecules of air, causing them to glow and produce beautiful curtains of light. 10.3

Behaviour differential rotation: the type of rotation possessed by the Sun which varies according to latitude, that is, it’s different as you go north or south of the Sun’s equator. 10.4

Chromosphere: the region of the Sun’s atmosphere that lies immediately above the photosphere, is about 2000 to 3000 kilometres thick, and whose spectrum consists of bright emission lines, indicating that this layer is composed of hot gases emitting light at discrete wavelengths. 10.3

Conduction: process by which heat is directly transmitted through a substance when there is a difference of temperature between adjoining regions caused by atomic or molecular collisions. 10.5

Convective zone: the outermost layer of the solar interior which is approximately 200,000 kilometres deep and transports energy from the edge of the radiative zone to the surface through giant convection cells. 10.3

Corona: the outermost part of the Sun’s atmosphere which extends millions of kilometres above the photosphere and emits about half as much light as the full moon. 10.3

Coronal hole: a region in the Sun’s outer atmosphere that appears darker because there is less hot gas there. 10.3

Coronal mass ejection (CME): event where immense quantities of coronal material—mainly protons and electrons—may also be ejected at high speeds (500–1000 kilometres per second) into interplanetary space. 10.4

Deuterium nucleus: an isotope (or version) of hydrogen that contains one proton and one neutron. 10.2

Equilibrium: a condition where a star is stable—neither expanding nor contracting—and where all the forces within it are balanced, so that at each point within the star, the temperature, pressure, density, and so on are maintained at constant values. 10.5

Eruptive prominences: relatively rare prominences that appear to send matter upward into the corona at high speeds. 10.4

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. 10.3

Hydrostatic equilibrium: balance between the weights of various layers, as in a star or Earth’s atmosphere, and the pressures that support them. 10.5

Ionized: atoms that are stripped of one or more of their electrons. 10.3

Penumbra: a region surrounding the umbra in a lasting sunspot that is less dark. 10.4

Photosphere: the layer where the Sun becomes opaque and marks the boundary past which we cannot see. 10.3

Plages: bright regions within the chromosphere that have higher temperature and density than their surroundings. 10.4

Plasma: the material in the Sun which is in the form of an ionized gas and acts much like a hot gas. 10.5

Positron: particle with the same mass as an electron, but positively charged. 10.2

Pressure (of a gas): the constant bombardment where the particles that constitute a gas are in rapid motion, frequently colliding with one another. 10.5

Prominences: phenomena higher in the Sun’s atmosphere that usually originate near sunspots. 10.4

Proton-proton chain: series of thermonuclear reactions by which nuclei of hydrogen are built up into nuclei of helium. 10.2

Quiescent prominences: graceful loops of plasma (ionized gas) that can remain nearly stable for many hours or even days. 10.4

Radiation: emission of energy as electromagnetic waves or photons also the transmitted energy itself. 10.5

Radiative zone: the region above the Sun’s core named for the primary mode of transporting energy across it; this region starts at about 25% of the distance to the solar surface and extends up to about 70% of the way to the surface. 10.3

Solar flare: a rapid eruption on the surface of the Sun that lasts for 5 to 10 minutes and releases a total amount of energy equivalent to that of perhaps a million hydrogen bombs. 10.4

Solar wind: a flow of hot, charged particles leaving the Sun. 10.3

Stellar convection: a process that occurs as currents of hot gas flow up and down through a star. 10.5

Sunspots: large, dark features seen on the surface of the Sun caused by increased magnetic activity. 10.4

Sunspot cycel: the semiregular 11-year period with which the frequency of sunspots fluctuates. 10.4

Sunspot maximum: a period of time when the the total number visible spots on the Sun is likely to be much greater. 10.4

Sunspot minimum: a period of time when the the total number visible spots on the Sun is likely to be much lower. 10.4

Sun’s core: an area located at the center of the Sun that is extremely dense and is the source of all of its energy. 10.3

Surge prominences: the most active prominences may move as fast as 1300 kilometres per second (almost 3 million miles per hour). 10.4

Umbra: inner dark core of a sunspot that lasts and develops. 10.4