![From Earth, the Sun appears so much larger and brighter than other stars because it is so close to …[Credits : Photo Researchers, Inc.]](http://media-2.web.britannica.com/eb-media/48/66848-003-E9776A96.gif)
The luminosity, or brightness, of the Sun has been increasing steadily since its formation. This phenomenon is important to Earth’s climate, because the Sun provides the energy to drive atmospheric circulation and constitutes the input for Earth’s heat budget. Low solar luminosity during Precambrian time underlies the faint young Sun paradox, described in the section Climates of early Earth.
![The Sun as imaged in extreme ultraviolet light by the Earth-orbiting Solar and Heliospheric …[Credits : NASA]](http://media-2.web.britannica.com/eb-media/19/73319-003-0410C7CB.gif)
Radiative energy from the Sun is variable at very small timescales, owing to solar storms and other disturbances, but variations in solar activity, particularly the frequency of sunspots, are also documented at decadal to millennial timescales and probably occur at longer timescales as well. The “Maunder minimum,” a period of drastically reduced sunspot activity between ad 1645 and 1715, has been suggested as a contributing factor to the Little Ice Age. (See below Climatic variation and change since the emergence of civilization.)
A-series-of-photographs-of-the-Grinnell-Glacier-taken-fromA series of photographs of the Grinnell Glacier taken from the summit of Mount Gould in Glacier …[Credits : 1938-T.J. Hileman/Glacier National Park Archives, 1981 - Carl Key/USGS, 1998 - Dan Fagre/USGS, 2006 - Karen Holzer/USGS]
Fishing-trawler-in-front-of-a-massive-iceberg-near-theFishing trawler in front of a massive iceberg near the coast of Greenland.[Credits : Pal Hermansen—Stone/Getty Images]
A-tropical-rainforest-in-Puerto-RicoA tropical rainforest in Puerto Rico.[Credits : Carlos Navajas—Stone/Getty Images]
Drought-resistant-plants-in-the-Repetek-Preserve-in-the-southeasternDrought-resistant plants in the Repetek Preserve in the southeastern Karakum Desert, Turkmenistan.[Credits : © Rodger Jackman/Oxford Scientific Films Ltd.]
Deciduous-forest-in-fall-coloration-Wasatch-Mountains-UtahDeciduous forest in fall coloration, Wasatch Mountains, Utah.[Credits : Dorothea W. Woodruff—EB Inc.]
Geologist-examining-fumaroles-on-the-crater-rim-of-Mount-ErebusGeologist examining fumaroles on the crater rim of Mount Erebus, Antarctica.[Credits : George Steinmetz/Corbis]
The-precession-of-Earths-axisThe precession of Earth’s axis.[Credits : Encyclopædia Britannica, Inc.]
From-Earth-the-Sun-appears-so-much-larger-and-brighterFrom Earth, the Sun appears so much larger and brighter than other stars because it is so close to …[Credits : Photo Researchers, Inc.]
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