Astronomy Ch 5

Front 1

achromatic lens

Back 1

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)

Front 2

active optics

Back 2

Thin telescope mirrors that are controlled by computers to maintain proper shape as the telescope moves. (p. 89)

Front 3

adaptive optics

Back 3

A computer-controlled optical system used to partially correct for seeing in an astronomical telescope. (p. 89)

Front 4

alt-azimuth mounting

Back 4

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)

Front 5

angstrom

Back 5

A unit of distance. 1 angstrom = 10-10 m. Commonly used to measure the wavelength of light. (p. 79)

Front 6

atmospheric window

Back 6

Wavelength region in which our atmosphere is transparent - at visual, infrared, and radio wavelengths. (p. 80)

Front 7

binding energy

Back 7

The energy needed to pull an electron away from its atom. (p. 95)

Front 8

black body radiation

Back 8

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)

Front 9

Cassegrain focus

Back 9

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)

Front 10

CCD

Back 10

See charge-coupled device.

Front 11

charge-coupled device (CCD)

Back 11

An electronic device consisting of a large array of light-sensitive elements used to record very faint images. (p. 90)

Front 12

chromatic aberration

Back 12

A distortion found in refracting telescopes because lenses focus different colors at slightly different distances. Images are consequently surrounded by color fringes. (p. 81)

Front 13

comparison spectrum

Back 13

A spectrum of known spectral lines used to identify unknown wavelengths in an object's spectrum. (p. 91)

Front 14

diffraction fringe

Back 14

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)

Front 15

electromagnetic radiation

Back 15

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)

Front 16

equatorial mounting

Back 16

A telescope mounting that allows motion parallel to and perpendicular to the celestial equator. (p. 89)

Front 17

eyepiece

Back 17

A short-focal-length lens used to enlarge the image in a telescope. The lens nearest the eye. (p. 80)

Front 18

false-color image

Back 18

A representation of graphical data with added or enhanced color to reveal detail. (p. 90)

Front 19

focal length

Back 19

The focal length of a lens is the distance from the lens to the point where it focuses parallel rays of light. (p. 80)

Front 20

grating

Back 20

A piece of material in which numerous microscopic parallel lines are scribed. Light encountering a grating is dispersed to form a spectrum. (p. 91)

Front 21

interferometry

Back 21

The observing technique in which separated telescopes combine to produce a virtual telescope with the resolution of a much-larger-diameter telescope. (p. 87)

Front 22

light pollution

Back 22

The illumination of the night sky by waste light from cities and outdoor lighting, which prevents the observation of faint objects. (p. 84)

Front 23

light-gathering power

Back 23

The ability of a telescope to collect light. Proportional to the area of the telescope's objective lens or mirror. (p. 82)

Front 24

magnifying power

Back 24

The ability of a telescope to make an image larger. (p. 84)

Front 25

nanometer (nm)

Back 25

A unit of distance equaling one-billionth of a meter (10-9 m). (p. 79)

Front 26

Newtonian focus

Back 26

The optical design in which a diagonal mirror reflects light out the side of the telescope tube for easier access. (p. 88)

Front 27

objective lens

Back 27

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)

Front 28

objective mirror

Back 28

In a reflecting telescope, the principal mirror (reflecting surface) that forms an image of the object viewed. (p. 80)

Front 29

photon

Back 29

A quantum of electromagnetic energy. Carries an amount of energy that depends inversely on its wavelength. (p. 78)

Front 30

polar axis

Back 30

In an equatorial telescope mounting, the axis that is parallel to Earth's axis. (p. 89)

Front 31

primary lens

Back 31

In a refracting telescope, the largest lens. (p. 80)

Front 32

primary mirror

Back 32

In a reflecting telescope, the largest mirror. (p. 80)

Front 33

prime focus

Back 33

The point at which the objective mirror forms an image in a reflecting telescope. (p. 88)

Front 34

radio interferometer

Back 34

Two or more radio telescopes that combine their signals to achieve the resolving power of a larger telescope. (p. 93)

Front 35

reflecting telescope

Back 35

A telescope that uses a concave mirror to focus light into an image. (p. 81)

Front 36

refracting telescope

Back 36

A telescope that forms images by bending (refracting) light with a lens. (p. 81)

Front 37

resolving power

Back 37

The ability of a telescope to reveal fine detail. Depends on the diameter of the telescope objective. (p. 83)

Front 38

Schmidt-Cassegrain focus

Back 38

The optical design that uses a thin corrector plate at the entrance to the telescope tube. A popular design for small telescopes. (p. 88)

Front 39

secondary mirror

Back 39

In a reflecting telescope, a mirror that directs the light from the primary mirror to a focal position. (p. 88)

Front 40

seeing

Back 40

Atmospheric conditions on a given night. When the atmosphere is unsteady, producing blurred images, the seeing is said to be poor. (p. 83)

Front 41

sidereal drive

Back 41

The motor and gears on a telescope that turn it westward to keep it pointed at a star. (p. 89)

Front 42

spectrograph

Back 42

A device that separates light by wavelengths to produce a spectrum. (p. 91)

Front 43

wavelength

Back 43

The distance between successive peaks or troughs of a wave. Usually represented by the Greek letter lambda. (p. 78)