Chapter 3 Flashcards
Telescope
Instrument used to capture as many photons as possible from a given region of the sky and concentrate them into a focused beam for analysis.
Reflecting telescope
A telescope that uses a mirror to gather and focus light from a distant object.
Prime focus
The point in a reflecting telescope where the mirror focuses incoming light to a point.
Refracting telescope
A telescope that uses a mirror to gather and focus light from a distant object.
Refraction
The tendency of a wave to bend as it passes from one transparent medium to another.
Images
The optical representation of an object produced when the object is reflected or refracted by a mirror or lens
Newtonian telescope
A reflecting telescope in which incoming light is intercepted before it reaches the prime focus and is deflected into an eyepiece at the side of the instrument.
Cassegrain telescope
A type of reflecting telescope in which incoming light hits the primary mirror and is then reflected upward toward the prime focus, where a secondary mirror reflects the light back down through a small hole in the main mirror into a detector or eyepiece.
Charged-coupled devices
An electronic device used for data acquisition; composed of many tiny pixels, each of which records a buildup of charge to measure the amount of light striking it.
Exposure time
Time spent gathering light from a source.
Collecting area
The total area of a telescope capable of capturing incoming radiation. The larger the telescope, the greater its collecting area and the fainter the objects it can detect
Angular resolution
The ability of a telescope to distinguish between adjacent objects in the sky.
Diffraction-limited resolution
Theoretical resolution that a telescope can have due to diffraction of light at the telescope’s aperture. Depends on the wavelength of radiation and the diameter of the telescope’s mirror.
Seeing
A term used to describe the ease with which good telescopic observations can be made from Earth’s surface, given the blurring effects of atmospheric turbulence.
Seeing disk
Roughly circular region on a detector over which a star’s pointlike images is spread, due to atmospheric turbulence.
Active optics
Collection of techniques used to increase the resolution of ground-based telescopes. Minute modifications are made to the overall configuration of an instrument as its temperature and orientation change; used to maintain the best possible focus at all times
Adaptive optics
Techniques used to increase the resolution of a telescope by deforming the shape of the mirror’s surface under computer control while a measurement is being taken; used to undo the effects of atmospheric turbulence.
Radio telescopes
Large instrument designed to detect radiation from space at radio wavelengths.
False color
Representation of an image in which color does not represent true visual color, but rather an invisible wavelength of radiation or some other property, such as temperature.
Interferometry
Technique in widespread use to dramatically improve the resolution of radio and infrared maps. Several telescopes observe the object simultaneously, and a computer analyzes how the signals interfere with each other.
Interferometer
Collection of two or more telescopes working together as a team, observing the same object at the same time and at the same wavelength. The effective diameter of an interferometer is equal to the distance between its outermost telescopes.
Infrared telescopes
Telescope designed to detect infrared radiation. Many such telescopes are designed to be lightweight so that they can be carried above (most of) Earth’s atmosphere by balloons, airplanes, or satellites.
Ultraviolet telescope
A telescope that is designed to collect radiation in the ultraviolet part of the spectrum. Earth’s atmosphere is partially opaque to these wavelengths, so ultraviolet telescopes are put on rockets, balloons, and satellites to get high above most or all of the atmosphere.
High-energy telescopes
Telescope designed to detect X- and gamma-ray radiation.
