Sunlight

An image of the Sun and of its radiation.

Sunlight is the light and energy that comes from the Sun. When this energy reaches the earth's surface, it is called insolation. What we experience as sunlight is really solar radiation. It is the radiation and heat from the Sun in the form of electromagnetic waves.

The atmosphere affects the amount of solar radiation received. When solar radiation travels through the atmosphere, some of it is absorbed by the atmosphere (16%). Some of it is scattered to space (6%). Some of it is reflected by clouds (28%). About 47% of it reaches the Earth's surface.

Without sunlight, there could not be life on the Earth. Plants need sunlight for the process of photosynthesis. During photosynthesis the plants use the energy of the sunlight, water, and carbon dioxide, to create glucose (sugar). The glucose can later be used by the plant for energy or animals eat the plant and the glucose in it. Plants need sunlight to grow green. Without enough sunlight but with enough water, the plant grows very tall very quickly, but looks yellow and dehydrated, although when touched, the leaves are very moist.

Solar radiation can be both good and bad for a person's health. When in the light, the human body uses the ultraviolet part of sunlight to make its own Vitamin D. Without sunscreen too much ultraviolet light can cause sunburn and skin cancer. Sun angle makes difference in seasons on Earth as well as in the length of day and night. A high angle makes the tropics hot, and a low angle makes the arctic cold.

Intensity of sunlight on planets of Solar System

Sunlight in the Antelope Canyon, Arizona.

Different bodies of the Solar System receive sunlight of different intensities. The table compares the amount of light received by each planet on the Solar System follows:

Planet	Perihelion - Aphelion distance (AU)	Solar radiation maximum and minimum (W/m²)	Forcing temperature variation for albedo = 1 (°C)
Mercury	0.3075 – 0.4667	14,446 – 6,272	94.6
Venus	0.7184 – 0.7282	2,647 – 2,576	2.2
Earth	0.9833 – 1.017	1,413 – 1,321	4.7
Mars	1.382 – 1.666	715 – 492	21.1
Jupiter	4.950 – 5.458	55.8 – 45.9	6.0
Saturn	9.048 – 10.12	16.7 – 13.4	5.0
Uranus	18.38 – 20.08	4.04 – 3.39	2.8
Neptune	29.77 – 30.44	1.54 – 1.47	0.6

Use of solar energy

Solar energy is used in many different ways by people all over the world both in its traditional way for heating, cooking or drying and to make electricity where other power supplies are absent, such as in remote places on Earth or in the space. Sometimes, it is cheaper to make electricity from sunlight than from coal or oil.

Sunlight Media

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  The Sun, as seen from low Earth orbit overlooking the International Space Station. This sunlight is not filtered by the lower atmosphere, which blocks much of the solar spectrum.

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  Sunrise over the Gulf of Mexico and Florida. Taken on 20 October 1968 from Apollo 7.

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  Solar spectrum compared to black-body at 5775 K

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  Solar spectral irradiance (watts per square metre per nanometre) above atmosphere (yellow) and at surface (red). Extreme UV and X-rays are produced (left of wavelength range) but comprise very small amounts of the Sun's total output power (area under the curve).

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  Sunlight on Mars is dimmer than on Earth. This photo of a Martian sunset was imaged by Mars Pathfinder.

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  Solar irradiance spectrum at top of atmosphere, on a linear scale and plotted against wavenumber

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  Sunlight shining through clouds, giving rise to crepuscular rays

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  Sunlight penetrating through a forest canopy in Germany

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  Édouard Manet: Le déjeuner sur l'herbe (1862–63)

Other websites

• Solar radiation - Encyclopedia of Earth