charge-coupled devices (CCDs): an electronic device consisting of an array of light-sensitive elements used to move free charges through an integrated circuit and display their original location as a digital image.
chromatic aberration: an optical problem common in lenses that are unable to bring all wavelengths of light into focus at the same focal point (see focus).
electric field: a physical field surrounding an electric charge specified by the force that would be exerted on another charge placed in the vicinity (see magnetic field).
electromagnetic radiation: Radiant energy in the form of oscillating electric and magnetic fields (see electric field, magnetic field).
electromagnetic spectrum: The full range of wavelengths or frequencies of electromagnetic radiation (see electromagnetic radiation, wavelength, frequency).
eyepiece: The lens used to focus light gathered by an optical telescope on one’s eye.
false-colour images: Images that use visible light to display concentrations of light observed at invisible wavelengths (see visible light invisible light, electromagnetic spectrum).
focal length: The distance from a lens or mirror at which light is brought into focus.
frequency (ν): The rate at which one full wavelength of electromagnetic radiation occurs (see wavelength, speed of light).
interferometer: a set of telescopes used to practice of interferometry.
interferometry: an astronomical technique in which multiple telescopes are combined in order to increase resolving power (see interferometer).
invisible light: electromagnetic radiation from any part of the electromagnetic spectrum except visible (see electromagnetic radiation, electromagnetic spectrum, visible light).
light-gathering power: a telescope’s ability to gather light, which depends on the area of its primary lens or mirror (see primary lens, primary mirror).
light pollution: light resulting from human activity that brightens the sky and pollutes astronomical data.
magnetic field: a physical field induced by an electric current or magnetic material, which is specified by the force would exert on moving charges in the vicinity (see electric field).
magnifying power: a telescope’s ability to magnify an image, which depends on the focal lengths of the telescope’s primary lens (or mirror) and that of the eyepiece used.
optical telescopes: telescopes used to observe visible light.
photoelectric effect: the phenomenon in which the light incident upon a material frees electrons from atoms (see photon).
photographic plate: A glass plate that has been coated with a light-sensitive silver emulsion, used in photography.
photometry: the science in which measurements are made of the intensity of visible light from a source.
photons: particles of electromagnetic radiation which are responsible for the photoelectric effect.
primary lens: the main lens in a refracting telescope used to gather and focus light.
primary mirror: the main mirror in a reflecting telescope used to gather and focus light.
radio telescopes: telescopes used to detect radio waves.
reflecting telescopes: optical telescopes that use mirrors to gather and focus light.
refracting telescopes: optical telescopes that use lenses to gather and focus light.
resolving power: the measure of a telescope’s ability to resolve fine image details.
secondary mirror: a second mirror which is needed in reflecting telescopes to direct light to an eyepiece or camera.
spectrograph: an instrument used to separate and measure the spectral content of electromagnetic radiation (see electromagnetic spectrum).
spectroscopy: the science that studies light spectra (see electromagnetic radiation, electromagnetic spectrum).
speed of light (c): the constant speed of all forms of electromagnetic radiation in empty space, equal to 300,000 km/s.
visible light: electromagnetic radiation from the visible part of the electromagnetic spectrum.
wavelength (λ): The length over which electromagnetic radiation completes one oscillation.
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