Rainbows and Spectra Glossary

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absorption: Absorption occurs when light heats what it falls on, instead of being reflected or transmitted. Depending on the material, certain wavelengths will be absorbed, and others reflected or transmitted. Use the "back" button to return to the lesson.

astronomer: Person who studies distant objects and events outside the earth's atmosphere, such as planets, comets, stars, galaxies, supernovae, and black holes. Use the "back" button to return to the lesson.
Axis: A line on the edge of a graph that represents the range of possible values for one piece of information about each object or entry. For example, a y-axis that represents possible numbers of things usually goes from 0 at the bottom to some whole number at the top. Use the "back" button to return to the lesson.

Common Era (C.E.): Dates expressed in the current Julian Calendar, formerly "B.C." are said to be in the "Common Era." Use the "back" button to return to the lesson.

dispersion, disperse: The way the different colors in the light from a source spread out into a spectrum when the light is refracted through a material like water or glass. To spread light into its component colors or wavelengths. Use the "back" button to return to the lesson.
element: Material made of a single kind of atom, all of which have a particular number of protons and electrons. Hydrogen has one proton and one electron. Helium has two. Carbon has six, and iron has 26 protons and 26 electrons.
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EUVE satellite: Extreme Ultraviolet Explorer satellite, launched by NASA in June, 1992 to survey the sky in 4 regions of the euv, and to make spectroscopic measurements of stars and other sources.
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extreme ultraviolet: Wavelength regime of the electromagnetic spectrum between x-rays and ultraviolet, from approximately 100 to 1000 Å.
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filter: A material that transmits some, but not all the light that falls on it. Stained glass, for example, filters light and transmits only certain colors. Use the "back" button to return to the lesson.

histogram: Graph of a spectrum with color or wavelength on the horizontal axis and intensity on the vertical axis. The histograms in this lesson show the intensity for each color as a vertical bar with a height equal to that color's intensity number on a scale of 0-20. The colors are ordered along the horizontal axis in the order they appear in a rainbow.
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H-R diagram: A graph of stars plotted with luminosity along the vertical axis and temperature (decreasing) along the horizontal axis. This causes certain types and ages of stars to cluster together. H-R diagrams are an extremely useful way to observe how stars are transformed during their lifetimes of billions of years. See one here.
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ionize, ionization: A process that removes or adds one or more electrons from a neutral atom or molecule ionizes it. Removing electrons makes the particle negative, so it is said to be negatively ionized. Adding electrons results in positive ionization The atom or molecule can also be described by its state of ionization.
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intensity: The strength of a signal, such as light or sound. For light, the intensity is the brightness, for sound it is the volume. For a given wavelength of light, the intensity tells you how much how much of that color of light is being produced by the source. Use the "back" button to return to the lesson.
opaque: Any material that doesn't transmit light is said to be opaque. Every opaque object has a characteristic color determined by what colors of light it reflects most. Use the "back" button to return to the lesson.; Bouncing of light when it encounters an opaque surface, that is a surface that doesn't transmit light. When light strikes a surface, the wavelengths that are reflected most become the color of the object; "what you see is what you get." Use the "back" button to return to the lesson.
refraction, refract: Bending of light as it passes through a surface, such as the surface of water or glass. Different colors of light bend by different amounts. Use the "back" button to return to the lesson.
spectrum: Light from any source that has been separated into its different colors, using a prism or other refractive device. A rainbow is a naturally occurring spectrum of sunlight. The plural of spectrum is spectra. Use the "back" button to return to the lesson.

state of ionization: The amount of ionization of an atom or molecule: how many electrons it has lost (or gained). In astronomy there is a convention for showing this next to the chemical symbol with roman numerals. For example Fe I is neutral iron, Fe II is missing one electron, Fe III is missing two, and so on. If the atom is positively ionized, a plus sign is used, as in Fe +II
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transmit, transmission: To let light pass through, as in a material like glass, water, or air. Light that is neither reflected nor absorbed is transmitted. Many materials transmit some wavelengths and reflect or absorb others. Use the "back" button to return to the lesson.

wave: A traveling, periodic (repeating) displacement in an extended medium, such as water, string, air, or a drumhead. Light behaves like a wave in a string. Sound waves reach our ears through the air. Use the "back" button to return to the lesson.
wavelength: The distance from one peak to the next in a light wave. The wavelength determines the color of the light. Shorter wavelengths carry more energy, and longer wavelengths carry less. Use the "back" button to return to the lesson.