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You are free: to share – to copy, distribute and transmit the work; to remix – to adapt the work; Under the following conditions: attribution – You must give appropriate credit, provide a link to the license, and indicate if changes were made.
A pyrheliometer is an instrument that can measure direct beam solar irradiance. [1] Sunlight enters the instrument through a window and is directed onto a thermopile which converts heat to an electrical signal that can be recorded. The signal voltage is converted via a formula to measure watts per square metre.
Disappearing-filament pyrometers can be used only if the object under study emits visible light similar to a hot black body; [3] this means that its temperature must be high enough (around 600 °C and up) and the object must not be fully transparent or highly reflective. For good accuracy, the object should appear dark gray or black when cold. [2]
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He developed a pyrheliometer and made, between 1837 and 1838, [5] the first quantitative measurements of the solar constant. His estimate was 1228 W/m 2, very close to the current estimate of 1367 W/m 2. Using the Dulong-Petit law inappropriately, he estimated the temperature of the Sun's surface to be around 1800 °C. [6]
Date/Time Thumbnail Dimensions User Comment; current: 14:37, 2 September 2021: 725 × 591 (147 KB): Mary Mark Ockerbloom: Uploaded a work by V. E. McKelvey from "Principles of the mineral resource classification system of the U.S. Bureau of Mines and U.S. Geological Survey : Geological Survey Bulletin 1450-A" by Thomas S. Kleppe and V. E. McKelvey, U.S. Bureau of Mines and U.S. Geological Survey.