Astronomy Ch 5
Terms
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- achromatic lens
- A telescope lens composed of two lenses ground from different kinds of glass and designed to bring two selected colors to the same focus and correct for chromatic aberration. (p. 82)
- active optics
- Thin telescope mirrors that are controlled by computers to maintain proper shape as the telescope moves. (p. 89)
- adaptive optics
- A computer-controlled optical system used to partially correct for seeing in an astronomical telescope. (p. 89)
- alt-azimuth mounting
- A telescope mounting that allows the telescope to move in altitude (perpendicular to the horizon) and in azimuth (parallel to the horizon). See also equatorial mounting. (p. 89)
- angstrom
- A unit of distance. 1 angstrom = 10-10 m. Commonly used to measure the wavelength of light. (p. 79)
- atmospheric window
- Wavelength region in which our atmosphere is transparent - at visual, infrared, and radio wavelengths. (p. 80)
- binding energy
- The energy needed to pull an electron away from its atom. (p. 95)
- black body radiation
- Radiation emitted by a hypothetical perfect radiator. The spectrum is continuous, and the wavelength of maximum emission depends on the body's temperature. (p. 97)
- Cassegrain focus
- The optical design in which the secondary mirror reflects light back down the tube through a hole in the center of the objective mirror. (p. 88)
- CCD
- See charge-coupled device.
- charge-coupled device (CCD)
- An electronic device consisting of a large array of light-sensitive elements used to record very faint images. (p. 90)
- chromatic aberration
- A distortion found in refracting telescopes because lenses focus different colors at slightly different distances. Images are consequently surrounded by color fringes. (p. 81)
- comparison spectrum
- A spectrum of known spectral lines used to identify unknown wavelengths in an object's spectrum. (p. 91)
- diffraction fringe
- Blurred fringe surrounding any image, caused by the wave properties of light. Because of this, no image detail smaller than the fringe can be seen. (p. 83)
- electromagnetic radiation
- Changing electric and magnetic fields that travel through space and transfer energy from one place to another; examples are light or radio waves. (p. 78)
- equatorial mounting
- A telescope mounting that allows motion parallel to and perpendicular to the celestial equator. (p. 89)
- eyepiece
- A short-focal-length lens used to enlarge the image in a telescope. The lens nearest the eye. (p. 80)
- false-color image
- A representation of graphical data with added or enhanced color to reveal detail. (p. 90)
- focal length
- The focal length of a lens is the distance from the lens to the point where it focuses parallel rays of light. (p. 80)
- grating
- A piece of material in which numerous microscopic parallel lines are scribed. Light encountering a grating is dispersed to form a spectrum. (p. 91)
- interferometry
- The observing technique in which separated telescopes combine to produce a virtual telescope with the resolution of a much-larger-diameter telescope. (p. 87)
- light pollution
- The illumination of the night sky by waste light from cities and outdoor lighting, which prevents the observation of faint objects. (p. 84)
- light-gathering power
- The ability of a telescope to collect light. Proportional to the area of the telescope's objective lens or mirror. (p. 82)
- magnifying power
- The ability of a telescope to make an image larger. (p. 84)
- nanometer (nm)
- A unit of distance equaling one-billionth of a meter (10-9 m). (p. 79)
- Newtonian focus
- The optical design in which a diagonal mirror reflects light out the side of the telescope tube for easier access. (p. 88)
- objective lens
- In a refracting telescope, the long-focal-length lens that forms an image of the object viewed. The lens closest to the object. (p. 80)
- objective mirror
- In a reflecting telescope, the principal mirror (reflecting surface) that forms an image of the object viewed. (p. 80)
- photon
- A quantum of electromagnetic energy. Carries an amount of energy that depends inversely on its wavelength. (p. 78)
- polar axis
- In an equatorial telescope mounting, the axis that is parallel to Earth's axis. (p. 89)
- primary lens
- In a refracting telescope, the largest lens. (p. 80)
- primary mirror
- In a reflecting telescope, the largest mirror. (p. 80)
- prime focus
- The point at which the objective mirror forms an image in a reflecting telescope. (p. 88)
- radio interferometer
- Two or more radio telescopes that combine their signals to achieve the resolving power of a larger telescope. (p. 93)
- reflecting telescope
- A telescope that uses a concave mirror to focus light into an image. (p. 81)
- refracting telescope
- A telescope that forms images by bending (refracting) light with a lens. (p. 81)
- resolving power
- The ability of a telescope to reveal fine detail. Depends on the diameter of the telescope objective. (p. 83)
- Schmidt-Cassegrain focus
- The optical design that uses a thin corrector plate at the entrance to the telescope tube. A popular design for small telescopes. (p. 88)
- secondary mirror
- In a reflecting telescope, a mirror that directs the light from the primary mirror to a focal position. (p. 88)
- seeing
- Atmospheric conditions on a given night. When the atmosphere is unsteady, producing blurred images, the seeing is said to be poor. (p. 83)
- sidereal drive
- The motor and gears on a telescope that turn it westward to keep it pointed at a star. (p. 89)
- spectrograph
- A device that separates light by wavelengths to produce a spectrum. (p. 91)
- wavelength
- The distance between successive peaks or troughs of a wave. Usually represented by the Greek letter lambda. (p. 78)