photoelectric photometer Quick reference
A Dictionary of Astronomy (3 ed.)
... photometer An instrument for measuring the brightness of a star by means of the electric current produced when its light falls on a light-sensitive surface (the photoelectric effect ). The light gathered by a telescope passes through a filter on to a light-sensitive surface known as the cathode . The cathode emits electrons which are multiplied within a photomultiplier so that the signal is easily measurable. Each photon detected by the cathode generates a pulse, and the number of pulses per second is directly proportional to the star’s...
photometer Quick reference
A Dictionary of Astronomy (3 ed.)
... An instrument for measuring the brightness of stars or other objects. In its widest sense the term can include the human eye or the photographic plate. Conventionally, the term is confined to instruments such as the photoelectric photometer , or area photometers based on CCDs or infrared arrays, whose output is directly proportional to the incident...
photoelectric magnitude Quick reference
A Dictionary of Astronomy (3 ed.)
... magnitude The brightness of a star or other object measured with a photoelectric photometer . This measurement requires correction for atmospheric extinction and comparison with at least one photometric standard star . The magnitude is expressed in terms of a system such as Johnson photometry or Strömgren photometry...
photometer Quick reference
A Dictionary of Physics (8 ed.)
...photometer An instrument used to measure luminous intensity , illumination, and other photometric quantities. The older types rely on visual techniques to compare a source of light with a standard source. More modern photometers use photoelectric cells based on the photoconductive, photoemissive, or photovoltaic effect. The photovoltaic types do not require an external power source and are therefore very convenient to use but are relatively insensitive. The photoemissive type usually incorporates a photomultiplier , especially for use in astronomy and...
polarimeter Quick reference
A Dictionary of Astronomy (3 ed.)
...of the polarizer with respect to the direction of polarization of the source. The intensity is measured with a photoelectric photometer with filters. For stars and other point sources the results are stated as the percentage of the light that is polarized. For extended sources, a false-colour image may be used, or the direction and strength of the polarization may be shown by arrows superimposed upon a normal image. A photometer combined with a polarimeter is termed a photopolarimeter . See also spectropolarimetry...
photometer n. Quick reference
A Dictionary of Psychology (4 ed.)
... n . An instrument for measuring luminous intensity , older types usually involving visual comparisons of the illumination from a specified light source with that from a standard comparison source, and more modern types using photoelectric cells that generate electrical signals in response to light. photometry n . The measurement of luminous intensity , luminous flux , and related phenomena, or the branch of physics concerned with these phenomena. [From Greek phos , photos light + metron a...
spectrometer Quick reference
A Dictionary of Astronomy (3 ed.)
... A spectrograph in which the output spectrum is scanned by a photoelectric photometer to produce a record of how the intensity of a spectrum varies with wavelength. A modern example is the radial velocity spectrometer , in which the positions of the spectral lines are measured to deduce the radial velocity of the star. Otherwise, spectrometers are now rarely used because CCD detectors can record large regions of a spectrum at once, and the device is then known as a spectrograph...
visual magnitude Quick reference
A Dictionary of Astronomy (3 ed.)
...of ranking stars in order of brightness and estimating equality between two stars, or a star and an artificial source. These were the only ways to measure visual magnitudes until the advent of the photovisual magnitude technique and photoelectric photometry . Now that magnitudes are measured precisely by photometers, it is more usual to use the apparent V magnitude...
photometry Quick reference
A Dictionary of Physics (8 ed.)
... In photometry, two types of measurement are used: those that measure luminous quantities rely on the use of the human eye (for example, to compare the illuminance of two surfaces); those called radiant quantities rely on the use of photoelectric devices to measure electromagnetic energy. See also photometer . http://www.kayelaby.npl.co.uk/general_physics/2_5/2_5_3.html Photometric data available at the NPL website...
densitometer Quick reference
A Dictionary of Physics (8 ed.)
...to measure the photographic density of an image on a film or photographic print. Densitometers work by letting the specimen transmit or reflect a beam of light and monitoring the transmitted or reflected intensity. They originally consisted of visual photometers but most instruments are now photoelectric. The simplest transmission densitometer consists of a light source, a photosensitive cell, and a microammeter: the density is measured in terms of the meter readings with and without the sample in place. They have a variety of uses, including detecting the...
exposure meters Reference library
Roger W. Hicks
The Oxford Companion to the Photograph
...The earliest commercially successful spot meter, the SEI Photometer ( 1947 ), had no ‘mid point’ index, just shadow and highlight indices. Spot meters can also be used to measure overall brightness ranges, in order to determine the need for modified development (for monochrome) or additional lighting or contrast‐reducing screens (for colour). Most spot meters read a 1‐degree circle and are photoelectronic, though the SEI read 0.5 degrees and was a sophisticated visual comparison photometer. Flash meters are variants on the three modern meter types. Many...
Instruments of Science Reference library
Deborah J. Warner
The Oxford Encyclopedia of the History of American Science, Medicine, and Technology
...and Space Administration (NASA) with help from the European Space Agency and operated by the Space Telescope Science Institute, was placed in a low earth orbit in 1990 ; it was built with a primary mirror of 2.4-meter aperture, as well as cameras, spectrographs, and photometers. Americans have been involved with astronomical photography since the 1840s and with astronomical spectroscopy since the 1860s. Notable here were the diffraction gratings produced on engines designed and constructed by Lewis Rutherfurd of New York and Henry Rowland of...
