Solar luminosity

Solar luminosity

The solar luminosity, L_odot, is a unit of luminosity (power emitted in the form of photons) conventionally used by astronomers to give the luminosities of stars.It is equal to the current accepted luminosity of the Sun, which is 3.839 × 1026 W, or 3.839 × 1033erg/s. [cite book
last = Carroll
first = Bradley W.
coauthors = Dale A. Ostlie
title = An Introduction to Modern Astrophysics
publisher = Pearson Addison Wesley
date = 2007
pages = Appendix A
month = September
isbn = 0-8053-0402-9
] Note that the Sun is a weak variable star and its luminosity therefore fluctuates.

Calculating with this constant

You can calculate how much solar power hits the Earth by comparing a cross sectional area of the Earth and the total surface area of a sphere with a radius equal to the distance of the earth from the sun.
* The Earth's radius is 3963 miles (6,378 km).
* The Earth's cross sectional area = π×radius2 = 49.3 million square miles (128,000,000 km²).
* The Sun's average distance is about 93 million miles (150,000,000 km).
* The surface area of a sphere = 4×π×radius2 = 1.09×1017 square miles (2.82×1017 km²).
* Power reaching the Earth = "P"(total) × Area(earth)/Area(sphere) = 1.77×1017 W.
* The power hitting a square meter of area on Earth: (square meter = 1/16092 square miles)
** Power over square meter = "P"(total)(1/16092)/area(sphere) = 1387 W "(the solar constant)"
* Estimates have been made that humans use about 12×1012 W.
* How much land area would be needed to power that?
** The best solar cells can produce about 33% efficiency.
** Area needed = 12×1012/(1387×0.33) = 26×109 m2 = 10122 square miles ~100×100 mile square. (More is needed since the sun is not always straight over head, and because some fraction of the radiation does not reach the surface due to clouds and atmospheric scattering.)

References

*

* cite book
last = Carroll
first = Bradley W.
coauthors = Dale A. Ostlie
title = An Introduction to Modern Astrophysics
publisher = Pearson Addison Wesley
date = 2007
pages = Appendix A
month = September
isbn = 0-8053-0402-9


Wikimedia Foundation. 2010.

Игры ⚽ Нужно решить контрольную?

Look at other dictionaries:

  • Solar variation — Solar variations are changes in the amount of solar radiation emitted by the Sun. There are periodic components to these variations, the principal one being the 11 year solar cycle (or sunspot cycle), as well as aperiodic fluctuations. Solar… …   Wikipedia

  • Solar cycle — The solar cycle, or the solar magnetic activity cycle, is the main source of periodic variation of all solar phenomena driving variations in space weather. [ [http://www7.nationalacademies.org/ssb/SSB Space weather97.pdf Space Weather: A Research …   Wikipedia

  • Solar radius — In astronomy, the solar radius is a unit of length used to express the size of stars. It is equal to the current radius of the Sun. Its value is::1,R {odot} = 6.960 imes 10^8,hbox{m} = 0.004652,hbox{AU} (Astronomical unit).The solar radius is… …   Wikipedia

  • Luminosity — has different meanings in several different fields of science.In photometry and color imagingIn photometry, luminosity is sometimes incorrectly used to refer to luminance, which is the density of luminous intensity in a given direction. The SI… …   Wikipedia

  • Solar mass — Weight of the Sun redirects here. For the song, see Tao of the Dead. Size and mass of very large stars: Most massive example, the blue Pistol Star (150 ). Others are Rho Cassiopeiae (40 …   Wikipedia

  • Solar System — This article is about the Sun and its planetary system. For other systems, see planetary system and star system. For a list of physical and orbital statistics for the Solar System s largest bodies, see List of gravitationally rounded objects of… …   Wikipedia

  • Eddington luminosity — The Eddington luminosity (also referred to as the Eddington limit) in a star is defined as the point where the gravitational force inwards equals the continuum radiation force outwards, assuming hydrostatic equilibrium and spherical symmetry.… …   Wikipedia

  • Formation and evolution of the Solar System — Artist s conception of a protoplanetary disk The formation and evolution of the Solar System is estimated to have begun 4.568 billion years ago with the gravitational collapse of a small part of a giant molecular cloud …   Wikipedia

  • History of Solar System formation and evolution hypotheses — Capture theory redirects here. For the solar capture theory, see this article s section on Solar System formation. For the lunar capture theory, see this article s section on lunar formation. Ideas concerning the origin and fate of the world date …   Wikipedia

  • Standard Solar Model — The Standard Solar Model (SSM) is the best current physical model of our sun. Very generally, in the Standard Solar Model the sun is a ball of mostly hydrogen plasma which is held together through self gravitation. At the core of the sun the… …   Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”