Glossary

Active Region: A temporary area of the solar atmosphere in which plages, sunspots, faculae, flares, and other features of the sun can be observed.

Anthropomorphic: The ascribing of human motivation and characterists to inanimate objects, animals or natural phenomena. ( go to where the term first appears in the text)

Archeoastronomy: The study of the astronomical practices, celestial lore, mythologies, religions and worldviews of all ancient cultures. Referred to, in essence, as the "anthropology of astronomy," to distinguish it from the "history of astronomy." ( go to where the term first appears in the text)

Aurora: A faint visual (optical) phenomenon on the earth associated with geomagnetic activity, which occurs mainly in the high-latitude night sky. Typical auroras are 100 to 250 km above the ground. The Aurora Borealis occurs in the Northern Hemisphere and the Aurora Australis occurs in the Southern Hemisphere. ( go to where the term first appears in the text)

Convection: The organized movement of large groups of molecules based on their relative densities or temperatures. A hot fluid or gas will move upward through a cooler liquid or gas. ( go to where the term first appears in the text)

Corona: The outermost layer of the solar atmosphere, characterized by low densities and high temperatures, often several million degrees kelvin. ( go to where the term first appears in the text).

Cosmic Ray: An extremely energetic charged particle, moving at nearly the speed of light.

Facula: A bright region of the photosphere seen in white light.

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

Gamma Rays: High-energy radiation observed during large, extremely energetic solar flares. ( go to where the term appears in the text).

Infrared: infrared radiation (IR) Infrared is electromagnetic radiation just beyond the visible spectrum. Infrared radiation has a wavelength longer than visible radiation and shorter than microwave radiation. Humans perceive infrared radiation as "heat radiation." ( go to where the term first appears in the text).

Magnetic Field: A field of magnetic force lines, usually referred to here as the pattern of magnetic force emanating from and surrounding the sun or any of the planets. For a detailed explanation of magnetic fields and magnetism, go to http://www.mpae.gwdg.de/documentation/Magnetosphere/Imagnet.html ( go to where the term first appears in the text).

Magnetic Storms: The term "magnetic storm," meaning a worldwide magnetic disturbance, was coined by Alexander von Humboldt (1769-1859). A naturalist who gained attention by exploring the jungles of Venezuela, Humboldt devoted much of his life to the promotion of science. He produced five volumes of "Kosmos" (startng the modern usage of that term), an encyclopaedic account covering the broad spectrum of the sciences. It was "Kosmos" that brought to the world's attention the discovery of the sunspot cycle by Heinrich Schwabe. After journeying the length of Siberia, Humboldt convinced the Czar to set up a network of magnetic observatories across the Russian lands, and additional stations were established throughout the British Empire, from Toronto to Tasmania. This network clearly showed that magnetic storms were essentially identical all over the world: a steep decrease of the field over twelve to twenty-four hours, followed by a gradual recovery, which lasted one to four days. The change in the magnetic field was small, but its world-wide scale suggested that something quite big was happening out in space. ( go to where the term first appears in the text).

Penumbra: The brighter area that surrounds the darker umbra or umbrae at the center of a sunspot.( go to where the term first appears in the text).

Plage: 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.

Plasma: Ionized gas. Any gas energized by (or containing) ions and electrons.

Photosphere: The lowest layer of the solar atmosphere; it is the solar surface that is visible in white-light images.

Prominence: Cloud-like features in the solar atmosphere that appear as bright structures in the corona above the solar limb, and as dark filaments when seen projected against the solar disk.

Sunspots: Temporary areas of concentrated magnetic field on the sun, where convection of hot matter from the sun's core is inhibited, resulting in a cooler, darker area on the photosphere of the sun. ( go to where the term first appears in the text).

Solar Maximum: The month(s) during the Solar Cycle when the twelve-month mean of monthly average sunspots numbers reaches a maximum. The most recent solar maximum occurred in July 1989. ( go to where the term first appears in the text).

Solar Minimum: The month(s) during the Solar Cycle when the twelve-month mean of monthly average sunspot numbers reaches a minimum. The most recent minimum occurred in September 1986.

Solar Wind: The outward flow of energetic particles and magnetic fields from the sun. Average speeds are about 350 km/sec

The Sun: One of the 100 billion stars in our galaxy. 1,390,000 km diameter. Temperature at the core: 15,600,000 k. Temperature at the surface: 5800 k.

Ultraviolet: Electromagnetic radiation at wavelengths shorter than the violet part of visible light. ( go to where the term first appears in the text).

Umbra: The term for the dark area at the center of a sunspot. ( go to where the term first appears in the text).

X-rays: Electromagnetic radiation of very short wavelength, and very high energy. X-rays have shorter wavelengths than ultraviolet light, but longer wavelengths than cosmic rays. ( go to where the term appears in the text).