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Snowden (physics)
A Snowden is a unit of soft X-ray emissivity The emissivity of the surface of a material is its effectiveness in emitting energy as thermal radiation. Thermal radiation is electromagnetic radiation that most commonly includes both visible radiation (light) and infrared radiation, which is n ..., equivalent to 10^ ROSAT counts s^ arcmin^. These units were chosen by S. L. Snowden when working with the ROSAT mission to create the ROSAT All-Sky Survey in order to make the surface brightness values fit into a two byte integer. References {{physics-stub Units of measurement ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Soft X-ray
An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10 Picometre, picometers to 10 Nanometre, nanometers, corresponding to frequency, frequencies in the range 30 Hertz, petahertz to 30 Hertz, exahertz ( to ) and energies in the range 145 electronvolt, eV to 124 keV. X-ray wavelengths are shorter than those of ultraviolet, UV rays and typically longer than those of gamma rays. In many languages, X-radiation is referred to as Röntgen radiation, after the German scientist Wilhelm Röntgen, Wilhelm Conrad Röntgen, who discovered it on November 8, 1895. He named it ''X-radiation'' to signify an unknown type of radiation.Novelline, Robert (1997). ''Squire's Fundamentals of Radiology''. Harvard University Press. 5th edition. . Spellings of ''X-ray(s)'' in English include the variants ''x-ray(s)'', ''xray(s)'', and ''X ray(s)''. The most familiar use of X-ra ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Emissivity
The emissivity of the surface of a material is its effectiveness in emitting energy as thermal radiation. Thermal radiation is electromagnetic radiation that most commonly includes both visible radiation (light) and infrared radiation, which is not visible to human eyes. A portion of the thermal radiation from very hot objects (see photograph) is easily visible to the eye. The emissivity of a surface depends on its chemical composition and geometrical structure. Quantitatively, it is the ratio of the thermal radiation from a surface to the radiation from an ideal black surface at the same temperature as given by the Stefan–Boltzmann law. The ratio varies from 0 to 1. The surface of a perfect black body (with an emissivity of 1) emits thermal radiation at the rate of approximately 448 watts per square metre at room temperature (, ). All real objects have emissivities less than 1.0, and emit radiation at correspondingly lower rates. Emissivities are important in several conte ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
