- Also called:
- sunshine
Sunlight
-
What is sunlight?
Sunlight is solar radiation that is visible at the Earth’s surface and is the largest source of energy received by the planet. Sunlight consists of close to 50% visible light, 45% infrared radiation, and smaller amounts of ultraviolet and other forms of electromagnetic radiation.
The amount of sunlight is dependent on the extent of daytime cloud cover. Some areas receive over 4,000 hours per year (more than 90 percent of the maximum), while others receive less than 2,000.
Air temperatures originate in the absorption of radiant energy from the Sun and are affected by the atmosphere, ocean, and land. Solar radiation is the single most important factor affecting climate.
9 Britannica Sources- solar energy: Importance and potential
- Synonyms of sunlight
- radiation: Intrinsic action
- photochemical reaction: Photochemical steps in photosynthesis
- human genetic disease: Ultraviolet radiation
- ultraviolet radiation
- electromagnetic radiation: Continuous spectra of electromagnetic radiation
- sunlight
- climate: Effects of the atmosphere
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
Where does sunlight come from?
Sunlight originates from nuclear fusion reactions within the Sun's core, where hydrogen atoms convert into helium, releasing vast energy. This process, driven by immense pressure and density, overcomes electrostatic repulsion between nuclei, enabling fusion.
The energy radiates outward, initially as gamma rays and kinetic energy, and is carried off by gamma-ray photons and neutrinos. As photons travel through the Sun, they undergo scattering, absorption, and re-emission, taking approximately 170,000 years to reach the surface. The final journey from the Sun's surface to Earth takes only eight minutes.
The Sun consists of hot gases like hydrogen and helium, with a surface temperature so high that all materials are in a gaseous state. The visible surface, or photosphere, emits radiation, resulting in the sunlight that reaches Earth.
3 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
What is solar radiation?
Solar radiation is electromagnetic radiation emitted by the Sun, including X-rays, ultraviolet and infrared radiation, radio emissions, and visible light. Earth receives a small fraction of the energy the Sun emits, but this amount is vital for life and natural processes. The Sun's energy output peaks at a wavelength of 0.47 micrometers, radiating about 8 kilowatts per square centimeter of its surface.
Sunlight, the solar radiation that is visible at Earth’s surface, is made of visible light (0.4 to 0.8 micrometers), ultraviolet light (less than 0.4 micrometers), and infrared radiation (more than 0.8 micrometers). The amount of sunlight varies depending on cloud cover, with some areas receiving over 4,000 hours per year and others less than 2,000.
4 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
What types of energy are found in solar radiation?
Solar radiation includes electromagnetic radiation like X-rays, ultraviolet and infrared radiation, radio emissions, and visible light. Sunlight consists of:
* Visible light, with wavelengths between 0.4 and 0.8 micrometers
* Ultraviolet light, with wavelengths shorter than 0.4 micrometers
* Infrared radiation, with wavelengths longer than 0.8 micrometersVisible light makes up nearly half of the total radiation received at the Earth's surface. Almost 50% of the total solar radiation is infrared, which has heat-producing qualities.
6 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
How does Earth's atmosphere affect solar radiation?
The Earth's atmosphere significantly modifies solar radiation. On average, 23% of incoming solar radiation is absorbed within the atmosphere by water vapor, clouds, and ozone, with ozone absorbing ultraviolet light and warming the stratosphere.
The atmosphere also scatters visible light through Rayleigh scattering, which explains why the sky appears blue. Additionally, the atmosphere acts as a radiative blanket, trapping heat through the greenhouse effect and maintaining Earth's surface temperature.
5 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
Why is solar radiation important for life on Earth?
Solar radiation is vital for sustaining life on Earth. Photosynthesis, which is carried out by plants, algae, and cyanobacteria, relies on solar energy and produces food and oxygen, which are essential for most organisms to survive. Solar radiation also drives the water cycle, influences land and water temperatures, and contributes to wind formation, all of which are key factors in shaping the Earth's climate patterns. Additionally, the ozone layer in the atmosphere, created by the interaction of solar radiation with air molecules, protects life by blocking harmful ultraviolet radiation from the Sun. Solar radiation also enables the production of vitamin D in the skin, which is important for calcium metabolism.
8 Britannica Sources- 16 Questions About Earth’s Atmosphere and Weather Answered: Why is the ozone layer important to Earth?
- solar radiation
- solar energy: Importance and potential
- vitamin D
- radiation: Effects on the eyes
- photochemical reaction: Photochemical steps in photosynthesis
- human genetic disease: Ultraviolet radiation
- climate: Distribution of radiant energy from the Sun
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
Sunlight, solar radiation that is visible at Earth’s surface. The amount of sunlight is dependent on the extent of the daytime cloud cover. Some places on Earth receive more than 4,000 hours per year of sunlight (more than 90 percent of the maximum possible), as in the Sahara; others receive less than 2,000 hours, as in regions of frequent storminess, such as Scotland and Iceland. Over much of the middle-latitude region of the world, the amount of sunlight varies regularly as the day progresses, owing to greater cloud cover in the early morning and during the late afternoon.
Ordinarily, sunlight is broken down into three major components: (1) visible light, with wavelengths between 0.4 and 0.8 micrometre, (2) ultraviolet light, with wavelengths shorter than 0.4 micrometre, and (3) infrared radiation, with wavelengths longer than 0.8 micrometre. The visible portion constitutes nearly half of the total radiation received at the surface of Earth. Although ultraviolet light constitutes only a very small proportion of the total radiation, this component is extremely important. It produces vitamin D through the activation of ergosterol. Unfortunately, the polluted atmosphere over large cities robs solar radiation of a significant portion of its ultraviolet light. Infrared radiation has its chief merit in its heat-producing quality. Close to half of total solar radiation received at the surface of Earth is infrared.
On its path through the atmosphere the solar radiation is absorbed and weakened by various constituents of the atmosphere. It is also scattered by air molecules and dust particles. Short wavelengths of light, such as blue, scatter more easily than do the longer red wavelengths. This phenomenon is responsible for the varying colour of the sky at different times of day. When the sun is high overhead, its rays pass through the intervening atmosphere almost vertically. The light thus encounters less dust and fewer air molecules than it would if the sun were low on the horizon and its rays had a longer passage through the atmosphere. During this long passage the dominant blue wavelengths of light are scattered and blocked, leaving the longer, unobstructed red wavelengths to reach Earth and lend their tints to the sky at dawn and dusk.
" height="20" alt="HEW Logo">
An effective absorber of solar radiation is ozone, which forms by a photochemical process at heights of 10–50 km (6–30 miles) and filters out most of the radiation below 0.3 micrometre. Equally important as an absorber in the longer wavelengths is water vapour. A secondary absorber in the infrared range is carbon dioxide. These two filter out much of the solar energy with wavelengths longer than 1 micrometre.
The Eppley pyrheliometer measures the length of time that the surface receives sunlight and the sunshine’s intensity as well. It consists of two concentric silver rings of equal area, one blackened and the other whitened, connected to a thermopile. The sun’s rays warm the blackened ring more than they do the whitened one, and this temperature difference produces an electromotive force that is nearly proportional to the sunlight’s intensity. The electromotive force is automatically measured and recorded and yields a continuous record of the duration and intensity of the periods of sunlight.