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...
photoelectric photometer
photoelectric magnitude
visual magnitude
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...
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...
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...
