Sunlight is Earth's primary source of energy. The only other source of energy the earth has are the fissionable materials generated by the cataclysmic death of another star. These fissionable materials trapped in the Earth's crust is what gives rise to geothermal energy, which drives the volcanism on Earth while also making it possible for mankind to fuel nuclear reactors. The solar constant is the amount of power that the Sun deposits per unit area that is directly exposed to sunlight. The solar constant is equal to approximately 1,368 W/m2 (watts per square meter) at a distance of one astronomical unit (AU) from the Sun (that is, on or near Earth). Sunlight on the surface of Earth is attenuated by the Earth's atmosphere so that less power arrives at the surface—closer to 1,000 W/m2 in clear conditions when the Sun is near the zenith.
Solar energy can be harnessed by a variety of natural and synthetic processes—photosynthesis by plants captures the energy of sunlight and converts it to chemical form (oxygen and reduced carbon compounds), while direct heating or electrical conversion by solar cells are used by solar power equipment to generate electricity or to do other useful work, sometimes employing concentrating solar power (that it is measured in suns). The energy stored in petroleum and other fossil fuels was originally converted from sunlight by photosynthesis in the distant past.
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Famous quotes containing the word sunlight:
“The sunlight on the garden
Hardens and grows cold,
We cannot cage the minute
Within its nets of gold,”
—Louis MacNeice (19071963)
“Anton Petrovich turned into the passage, followed the arrow to men, mankind, human beings, marched past the toilet, past the kitchen, gave a start when a cat darted under his feet, quickened his step, reached the end of the passage, pushed open a door, and a shower of sunlight splashed his face.”
—Vladimir Nabokov (18991977)
“Spite of all the Indian-summer sunlight on the hither side of Hawthornes soul, the other sidelike the dark half of the physical sphereis shrouded in a blackness, ten times black.”
—Herman Melville (18191891)