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Thermal radiation can be used to detect objects or phenomena normally invisible to the human eye. [[infrared camera|Thermographic cameras]] create an image by sensing infrared radiation. These images can represent the temperature gradient of a scene and are commonly used to locate objects at a higher temperature than their surroundings. In a dark environment where visible light is at low levels, infrared images can be used to locate animals or people due to their body temperature. [[Cosmic microwave background radiation]] is another example of thermal radiation.
[[Black-body radiation|Blackbody radiation]] is a concept used to analyze thermal radiation in idealized systems. This model applies if a
==Overview==
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=== Renaissance ===
During the
Earlier, in 1589, [[Giambattista della Porta]] reported on the heat
=== Enlightenment ===
In 1761, [[Benjamin Franklin]] wrote a letter describing his experiments on the relationship between color and heat absorption.<ref>Cohen, I. B. (1943). [http://www.jstor.org/stable/225739 Franklin’s Experiments on Heat Absorption as a Function of Color] {{Webarchive|url=https://web.archive.org/web/20240925182208/https://www.jstor.org/stable/225739 |date=25 September 2024 }}. ''Isis'', ''34''(5), 404–407.</ref> He found that darker color clothes got hotter when exposed to sunlight than lighter color clothes. One experiment he performed consisted of placing square pieces of cloth of various
=== Caloric theory ===
{{main|Caloric theory}}
[[Antoine Lavoisier]] considered that radiation of heat was concerned with the condition of the surface of a physical body rather than the material of which it was composed.<ref name=":22">{{Citation |last=Brown |first=Sanborn C. |title=The Caloric Theory |date=1967 |work=Men of Physics: Benjamin Thompson – Count Rumford |pages=16–24 |url=http://dx.doi.org/10.1016/b978-0-08-012179-6.50008-3 |access-date=2021-12-03 |publisher=Elsevier |doi=10.1016/b978-0-08-012179-6.50008-3 |isbn=9780080121796 |archive-date=6 October 2024 |archive-url=https://web.archive.org/web/20241006084656/https://www.sciencedirect.com/unsupported_browser |url-status=live }}</ref> Lavoisier described a poor radiator to be a substance with a polished or smooth surface as it possessed its molecules lying in a plane closely bound together thus creating a surface layer of caloric fluid which insulated the release of the rest within.<ref name=":22" /> He described a
In his first memoir, [[Augustin-Jean Fresnel]] responded to a view he extracted from a French translation of [[Isaac Newton]]'s ''[[Optics]]''. He says that Newton imagined particles of light traversing space uninhibited by the caloric medium filling it, and refutes this view (never actually held by Newton) by saying that a body under illumination would increase indefinitely in heat.<ref>{{cite book |last=Gillispie |first=Charles Coulston |url=https://archive.org/details/edgeofobjectivit00char/page/408 |title=The Edge of Objectivity: An Essay in the History of Scientific Ideas |publisher=Princeton University Press |year=1960 |isbn=0-691-02350-6 |pages=[https://archive.org/details/edgeofobjectivit00char/page/408 408–9] |author-link1=Charles Coulston Gillispie |url-access=registration}}</ref>
In [[Marc-Auguste Pictet]]'s famous [[Pictet's experiment|experiment of 1790]], it was reported that a thermometer detected a lower temperature when a set of
In 1791, [[Pierre Prevost (physicist)|Pierre Prevost]] a colleague of Pictet, introduced the concept of [[radiative equilibrium]], wherein all objects both
The discovery of infrared radiation is ascribed to astronomer [[William Herschel]]. Herschel published his results in 1800 before the [[Royal Society of London]]. Herschel used a [[Triangular prism (optics)|prism]] to [[refract]] light from the [[sun]] and detected the calorific rays, beyond the [[red]] part of the spectrum,
===
▲First, the earlier theory which originated from the concept of a hypothetical medium referred as [[Luminiferous aether|aether]]. Ether supposedly fills all evacuated or non-evacuated spaces. The transmission of light or of [[radiant heat]] are allowed by the propagation of [[electromagnetic waves]] in the aether.<ref name="hsu">Hsu, Shao Ti. ''Engineering Heat Transfer''. Blacksburg, Virginia:D. Van Nostrand Company, Inc.,1962.</ref> [[television]] and [[radio]] broadcasting waves are types of electromagnetic waves with specific [[wavelengths]].<ref name="becker">Becker, Martin. ''Heat Transfer a Modern Approach'' New York: Plenum Publishing Corporation, 1986.</ref> All [[electromagnetic waves]] travel at the same speed; therefore, shorter [[wavelengths]] are associated with high frequencies. Since every body or fluid is submerged in the ether, due to the vibration of the molecules, any body or fluid can potentially initiate an electromagnetic wave. All bodies generate and receive electromagnetic waves at the expense of its stored energy.<ref name="becker" />
In 1860, [[Gustav Kirchhoff]] published a mathematical description of [[thermal equilibrium]] (i.e. [[Kirchhoff's law of thermal radiation]]).<ref name=":7" />{{Rp|pages=275–301}} By 1884 the emissive power of a perfect blackbody was inferred by [[Josef Stefan]] using [[John Tyndall]]'s experimental measurements, and derived by [[Ludwig Boltzmann]] from fundamental statistical principles.<ref>{{cite journal |last1=Boltzmann |first1=Ludwig |date=1884 |title=Ableitung des Stefan'schen Gesetzes, betreffend die Abhängigkeit der Wärmestrahlung von der Temperatur aus der electromagnetischen Lichttheorie |trans-title=Derivation of Stefan's law, concerning the dependency of heat radiation on temperature, from the electromagnetic theory of light |url=https://babel.hathitrust.org/cgi/pt?id=uc1.a0002763670;view=1up;seq=305 |journal=Annalen der Physik und Chemie |language=de |volume=258 |issue=6 |pages=291–294 |bibcode=1884AnP...258..291B |doi=10.1002/andp.18842580616 |doi-access=free |access-date=25 March 2024 |archive-date=29 July 2020 |archive-url=https://web.archive.org/web/20200729024251/https://babel.hathitrust.org/cgi/pt?id=uc1.a0002763670 |url-status=live }}</ref> This relation is known as [[Stefan–Boltzmann law]].
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