Any of a number of atmospheric phenomena which appear as luminous patterns in the sky They do not directly cause adverse weather They include halos, coronas rainbows, and fogbows
An instrument for measuring the intensity of light, or, more especially, for comparing the relative intensities of different lights, or their relative illuminating power
A light meter which when attached to the eyepiece of a telescope can measure the brightness of stars The photometer will read out a number proportional to brightness If we first look at stars whose brightness we know, we can use our photometer to measure the brightness of a unknown star We use the SSP-3 photometers made by OPTEC Inc
Instrument for measuring photometric quantities such as luminance, illuminance, luminous intensity, and luminous flux An instrument for measuring the brightness of an object It has been suggested that this name be reserved for those instruments which have been adjusted to match the wavelength response of the human eye, but established usage is not yet this consistent, and radiometers are sometimes called photometers
An instrument for measuring the intensity of light or the relative intensity of a pair of lights Also called an illuminometer If the instrument is designed to measure the intensity of light as a function of wavelength, it is called a spectrophotometer Photometers may be divided into two classes: photoelectric photometers in which a photoelectric cell is used to compare electrically the intensity of an unknown light with that of a standard light, and visual photometers in which the human eye performs the function of a photo cell A photometer used to measure the intensity of a distant light is referred to as a telephotometer or transmissometer