solar constant


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solar constant,

the average amount of radiant energy received by the earth's atmosphere from the sun; its value is about 2 calories per min incident on each square centimeter of the upper atmosphere. The actual value of the energy varies with several factors; the most important factor is the earth's distance from the sun, which changes because of the earth's elliptical orbit. For computing the value of the solar constant, the astronomical unitastronomical unit
(AU), mean distance between the earth and sun; one AU is c.92,960,000 mi (149,604,970 km). The astronomical unit is the principal unit of measurement within the solar system, e.g., Mercury is just over 1-3 AU and Pluto is about 39 AU from the sun.
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, or average earth-sun distance, is used.
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solar constant

The total energy radiated by the Sun that passes perpendicularly through unit area per unit time at a specified distance from the Sun. It is given by the ratio L /4πr 2, where L is the luminosity of the Sun and r the distance. The value measured at the mean Sun–Earth distance is about 1.367 kilowatts per square meter. Instruments on satellites such as the Solar Maximum Mission have shown that variations in the solar constant occur, the energy flux being reduced when sunspots are present, by an amount proportional to the area of the spots.
Collins Dictionary of Astronomy © Market House Books Ltd, 2006
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Solar Constant

 

the amount of radiant energy received from the sun in 1 min by a surface that is perpendicular to the sun’s rays, is 1 cm2 in area, and is located outside the earth’s atmosphere at the earth’s mean distance from the sun. Knowledge of the exact value of the solar constant is very important for the study of heat-exchange processes in the earth’s atmosphere and for the investigation of processes occurring in the sun.

The first attempt to determine the solar constant was made by the French scientist C. S. M. Pouillet in 1837. An important contribution to early investigations of the solar constant was made by the Russian scientists R. N. Savel’ev and A. P. Ganskii. Up to the mid-20th century, the solar constant was determined from measurements of solar radiation at the earth’s surface for different altitudes of the sun. This method permits the absorption and scattering of sunlight by the earth’s atmosphere to be taken into account. The first direct determinations of the solar constant were made in the 1960’s, when it became technologically feasible to lift instruments outside the earth’s atmosphere by means of rockets and artificial earth satellites.

On the basis of analysis of a large number of research projects carried out in the USSR, the USA, and other countries, the value of 1.95 calories/cm2-min, or 136 milliwatts/cm2, has been derived for the solar constant. The accuracy of this value is approximately 1 percent. The solar constant apparently varies slightly with time. Many years of painstaking measurements, however, are necessary before it can be determined how these variations occur.

REFERENCES

Kondrat’ev, K. Ia. Aktinometriia. Leningrad, 1965.
Makarova, E. A., and A. V. Kharitonov. Raspredelenie energii v speklre Solntsa i solnechnaia postoiannaia. Moscow, 1972.

M. DZH. GUSEINOV

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.

solar constant

[′sō·lər ′kän·stənt]
(meteorology)
The rate at which energy from the sun is received just outside the earth's atmosphere on a surface normal to the incident radiation and at the earth's mean distance from the sun; it is approximately 1367 watts per square meter.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

solar constant

The average rate at which radiant energy is received by the earth from the sun; equal to 430 Btu per hr per sq ft (1.94 cal per min per sq cm); a constant employed in calculating air-cooling loads due to the effects of solar radiation on buildings.
McGraw-Hill Dictionary of Architecture and Construction. Copyright © 2003 by McGraw-Hill Companies, Inc.

solar constant

The solar constant (as defined for the planet Earth) is the power collected at the top of the atmosphere by a unit area perpendicular to the light path. In practice, the unit area is 1 m squared (m2). Its value is about 1.98 calories per minute incident on each square centimeter (approximately 127.7 calories incident per minute on each square inch) of the upper atmosphere. The solar constant is expressed normally as watts per square meter, and its value in this unit is 1,368 w/m2. The actual value of the energy varies with several factors; the most important factor is the earth's distance from the sun, which changes because of the earth's elliptical orbit.
An Illustrated Dictionary of Aviation Copyright © 2005 by The McGraw-Hill Companies, Inc. All rights reserved
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This photo-text essay explores the implications of the poem sequence "Solar Constant" for a queer Puerto Rican Latinx poet as he contemplates his mortality, the cosmos, and our dying sun among hundreds of billions of stars in the mysterious night skies.
This radiation energy can then be used to calculate the solar constant value which is adduced by the World Radiation Center (WRC) as shown by (1) [4]
Obliquity: 23.446[degrees] Eccentricity: 0.016724 Solar Constant: 1367 W/[m.sup.2] Perihelion Day: 2 mvelp: 77.961[degrees] Gases CO2 (ppm) 400 N2O (ppm) 326 Methane (ppb) 1750 CFC-11 (ppt) 236 CFC-12 (ppt) 527 Note: Table made from bar graph.
The solar constant values, specific of each one of the OLI-Landsat 8 bands, used in the albedo calculation, showed great differentiation between the studied days.
Standard values for the solar constant and its spectral components.
The generally accepted solar constant of ll8*108MJ*[m.sup.2]*[day.sup.-1] is a satellite-measured yearly average.
Langley used an infrared bolometer to measure the solar constant in the 1880s.
But the sunspot deficiency could have been symptomatic of some change in the sun's total brightness -- the so-called solar constant. Eddy suggested that the frigid conditions could have developed if the sun's total radiation had dimmed by only 1 percent.
In particular, Mount Montezuma in the Atacama Desert, Chile, was identified by the pioneers of solar observation as an ideal place to conduct the search for variations of the solar constant estimated from Earth's surface.
Other input data were determined as follows: maximum sunshine hours (N) from Cooper [8]; total daily extraterrestrial solar irradiation ([R.sub.ext]) and hour angle ([[omega].sub.s]) from Iqbal [9]; solar constant from Royal Meteorological Institute of Belgium.
Of course Max may well know that it is the stable thermic radiation of the Sun, known as the Solar Constant, which has created life on Earth - thanks to the Sun being at a safe distance.
Climate forecasters and others have long espoused the notion of a "solar constant," in which the long-term brightness remains unchanged despite short-term cyclic fluctuations.