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81-797: In Europe maerl beds occur throughout the Mediterranean, along most of the Atlantic coast from Portugal to Norway, and in the English Channel, Irish Sea and North Sea. The distribution of maerl is dependent on water movement, light and salinity concentration. Maerl beds occur in the photic zone , and can be found to around 30 m depth in the British Isles and up to 120 m deep in the Mediterranean. Maerl deposits can reach up to 10 m thick, but are usually much thinner; carbon dating has shown that they can be more than 5500 years old. In

162-633: A day, the highest amount of sunlight on a horizontal surface occurs in January at the South Pole (see insolation ). Dividing the irradiance of 1,050 W/m by the size of the Sun's disk in steradians gives an average radiance of 15.4 MW per square metre per steradian. (However, the radiance at the center of the sun's disk is somewhat higher than the average over the whole disk due to limb darkening .) Multiplying this by π gives an upper limit to

243-521: A dive light. Water in the open ocean appears clear and blue because it contains much less particulate matter , such as phytoplankton or other suspended particles, and the clearer the water, the deeper the light penetration. Blue light penetrates deeply and is scattered by the water molecules, while all other colours are absorbed; thus the water appears blue. On the other hand, coastal water often appears greenish. Coastal water contains much more suspended silt and algae and microscopic organisms than

324-424: A fast rate. In fact, ninety five percent of photosynthesis in the ocean occurs in the photic zone. Therefore, if we go deeper, beyond the photic zone, such as into the compensation point , there is little to no phytoplankton, because of insufficient sunlight. The zone which extends from the base of the euphotic zone to the aphotic zone is sometimes called the dysphotic zone. Ninety percent of marine life lives in

405-406: A food source. Detritivores and scavengers are rare in the photic zone. Microbial decomposition of dead organisms begins here and continues once the bodies sink to the aphotic zone where they form the most important source of nutrients for deep sea organisms. The depth of the photic zone depends on the transparency of the water. If the water is very clear, the photic zone can become very deep. If it

486-456: A large impact on those who reside in it. The depth is, by definition, where radiation is degraded down to 1% of its surface strength. Accordingly, its thickness depends on the extent of light attenuation in the water column. As incoming light at the surface can vary widely, this says little about the net growth of phytoplankton. Typical euphotic depths vary from only a few centimetres in highly turbid eutrophic lakes, to around 200 meters in

567-562: A less clear, and probably more complicated fashion, with Earth's climate responses than earlier assumed, fueling broad avenues of new research in "the connection of the Sun and stratosphere, troposphere, biosphere, ocean, and Earth's climate". The spectrum of surface illumination depends upon solar elevation due to atmospheric effects, with the blue spectral component dominating during twilight before and after sunrise and sunset, respectively, and red dominating during sunrise and sunset. These effects are apparent in natural light photography where

648-428: A nearly perfect circle, and at other times stretching out to an orbital eccentricity of 5% (currently 1.67%). As the orbital eccentricity changes, the average distance from the Sun (the semimajor axis does not significantly vary, and so the total insolation over a year remains almost constant due to Kepler's second law , where A {\displaystyle A} is the "areal velocity" invariant. That is,

729-463: A number of states in the world. For many people with light skin, one purpose for sunbathing is to darken one's skin color (get a sun tan), as this is considered in some cultures to be attractive, associated with outdoor activity, vacations/holidays , and health. Some people prefer naked sunbathing so that an "all-over" or "even" tan can be obtained, sometimes as part of a specific lifestyle. Controlled heliotherapy , or sunbathing, has been used as

810-537: A risk factor for skin cancer, "sun avoidance may carry more of a cost than benefit for over-all good health". A study found that there is no evidence that UV reduces lifespan in contrast to other risk factors like smoking, alcohol and high blood pressure. Elevated solar UV -B doses increase the frequency of DNA recombination in Arabidopsis thaliana and tobacco ( Nicotiana tabacum ) plants. These increases are accompanied by strong induction of an enzyme with

891-418: A room less than fluorescent or incandescent lighting. Multiplying the figure of 1,050 watts per square meter by 93 lumens per watt indicates that bright sunlight provides an illuminance of approximately 98,000 lux ( lumens per square meter) on a perpendicular surface at sea level. The illumination of a horizontal surface will be considerably less than this if the Sun is not very high in the sky. Averaged over

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972-429: A series of physical, chemical, and biological processes that supply nutrients into the upper water column . The photic zone is home to the majority of aquatic life due to the activity ( primary production ) of the phytoplankton. The thicknesses of the photic and euphotic zones vary with the intensity of sunlight as a function of season and latitude and with the degree of water turbidity. The bottommost, or aphotic, zone

1053-479: A treatment for psoriasis and other maladies. Skin tanning is achieved by an increase in the dark pigment inside skin cells called melanocytes , and is an automatic response mechanism of the body to sufficient exposure to ultraviolet radiation from the Sun or from artificial sunlamps. Thus, the tan gradually disappears with time, when one is no longer exposed to these sources. The ultraviolet radiation in sunlight has both positive and negative health effects, as it

1134-704: A variety of niches that support high associated invertebrate and algal biodiversity. Maerl beds act as nursery areas for the juvenile stages of commercial species such as juvenile cod Gadus morhua , saithe Pollachius virens , Pollack Pollachius pollachius and juvenile scallops Aequipecten opercularis . Maerl beds offer physical refuge and protection from predation as well as productive feeding grounds but are easily damaged by dredging and towed fishing gear. Maerl has no tolerance for desiccation. Maerl has been extracted for centuries mainly for use as an agricultural fertilizer. The amount extracted increased in

1215-442: Is diffused . Sources estimate a global average of between 164 watts to 340 watts per square meter over a 24-hour day; this figure is estimated by NASA to be about a quarter of Earth's average total solar irradiance . The ultraviolet radiation in sunlight has both positive and negative health effects, as it is both a requisite for vitamin D 3 synthesis and a mutagen . Sunlight takes about 8.3 minutes to reach Earth from

1296-490: Is a measure of flux density , is the amount of incoming solar electromagnetic radiation per unit area that would be incident on a plane perpendicular to the rays, at a distance of one astronomical unit (AU) (roughly the mean distance from the Sun to Earth). The "solar constant" includes all types of solar radiation, not just the visible light . Its average value was thought to be approximately 1,366 W/m , varying slightly with solar activity , but recent recalibrations of

1377-457: Is a popular fertilizer for organic gardening . It was also dredged off Falmouth, Cornwall , but this ceased in 2004. Scientists investigated Falmouth maerl and found that L. corallioides predominated down to 6 m and P. calcareum from 6–10 m. A 2024 survey by researchers from the University of Exeter , commissioned by Cornwall Council's Blue Natural Capital Project, found that

1458-410: Is ample sunlight. Some common places for sunbathing include beaches , open air swimming pools , parks , gardens , and sidewalk cafes . Sunbathers typically wear limited amounts of clothing or some simply go nude . For some, an alternative to sunbathing is the use of a sunbed that generates ultraviolet light and can be used indoors regardless of weather conditions. Tanning beds have been banned in

1539-437: Is both a principal source of vitamin D 3 and a mutagen . A dietary supplement can supply vitamin D without this mutagenic effect, but bypasses natural mechanisms that would prevent overdoses of vitamin D generated internally from sunlight. Vitamin D has a wide range of positive health effects, which include strengthening bones and possibly inhibiting the growth of some cancers. Sun exposure has also been associated with

1620-593: Is extracted from subfossil beds in Bantry Bay by Celtic Sea Minerals. The maerl-forming species Lithothamion corallioides and Phymatolithon calcareum are listed in Annex V of the EC Habitats Directive. Used as a soil conditioner, it is dredged from the sea floor and crushed to a powder. The slow growth of individual nodules and their accumulation in beds over a millennial timescale means that there

1701-569: Is fueled by light from the Sun. Most autotrophs , such as plants, use the energy of sunlight, combined with carbon dioxide and water, to produce simple sugars—a process known as photosynthesis . These sugars are then used as building-blocks and in other synthetic pathways that allow the organism to grow. Heterotrophs , such as animals, use light from the Sun indirectly by consuming the products of autotrophs, either by consuming autotrophs, by consuming their products, or by consuming other heterotrophs. The sugars and other molecular components produced by

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1782-515: Is left at 100 metres. No light penetrates beyond 1000 metres. In addition to overall attenuation, the oceans absorb the different wavelengths of light at different rates. The wavelengths at the extreme ends of the visible spectrum are attenuated faster than those wavelengths in the middle. Longer wavelengths are absorbed first; red is absorbed in the upper 10 metres, orange by about 40 metres, and yellow disappears before 100 metres. Shorter wavelengths penetrate further, with blue and green light reaching

1863-466: Is needed; only a handful of objects in the Solar System have been discovered that are known to orbit farther than such a distance, among them 90377 Sedna and (87269) 2000 OO 67 . On Earth, the solar radiation varies with the angle of the Sun above the horizon , with longer sunlight duration at high latitudes during summer, varying to no sunlight at all in winter near the pertinent pole. When

1944-473: Is no possibility of maerl keeping up with dredging for this purpose. Maerl should be considered as a non-renewable resource , and readily available alternative products (e.g., garden lime) make modern day exploitation controversial. Photic zone The photic zone (or euphotic zone , epipelagic zone , or sunlight zone ) is the uppermost layer of a body of water that receives sunlight , allowing phytoplankton to perform photosynthesis . It undergoes

2025-485: Is the aphotic (or midnight) zone, where no light penetrates. This region includes the majority of the ocean volume, which exists in complete darkness. Phytoplankton are unicellular microorganisms which form the base of the ocean food chains . They are dominated by diatoms , which grow silicate shells called frustules . When diatoms die their shells can settle on the seafloor and become microfossils . Over time, these microfossils become buried as opal deposits in

2106-442: Is the region of perpetual darkness that lies beneath the photic zone and includes most of the ocean waters. In the photic zone, the photosynthesis rate exceeds the respiration rate. This is due to the abundant solar energy which is used as an energy source for photosynthesis by primary producers such as phytoplankton. These phytoplankton grow extremely quickly because of sunlight's heavy influence, enabling it to be produced at

2187-431: Is very murky, it can be only fifty feet (fifteen meters) deep. Animals within the photic zone use the cycle of light and dark as an important environmental signal, migration is directly linked to this fact, fishes use the concept of dusk and dawn when its time to migrate, the photic zone resembles this concept providing a sense of time. These animals can be herrings and sardines and other fishes that consistently live within

2268-549: The British Isles maerl is composed of three species of coralline algae growing loose in beds of fragmented nodules in the sub-littoral. The species generally involved are: Lithothamnion corallioides , Lithothamnion glaciale and Phymatolithon calcareum . Maerl is dredged from the sea floor and crushed to form a powder. It is still harvested around the coasts of Brittany in France and Bantry Bay , Ireland , and

2349-468: The Fal and Helford Estuary Special Area of Conservation supports an 880 hectare bed of maerl. Chemical analysis of maerl showed that it contained 32.1% CaCO 3 and 3.1% MgCO 3 (dry weight). The ecology of maerl habitats has received very little attention in contrast to other marine ecosystems such as kelp forests or sea grass beds. Maerl beds provide a complex habitat for a wide range of taxa with

2430-476: The Sun , in particular infrared , visible , and ultraviolet light. On Earth , sunlight is scattered and filtered through Earth's atmosphere as daylight when the Sun is above the horizon . When direct solar radiation is not blocked by clouds , it is experienced as sunshine , a combination of bright light and radiant heat (atmospheric). When blocked by clouds or reflected off other objects , sunlight

2511-422: The attenuation by Earth's atmosphere have to be taken into account. The extraterrestrial solar illuminance ( E ext ), corrected for the elliptic orbit by using the day number of the year (dn), is given to a good approximation by where dn=1 on January 1; dn=32 on February 1; dn=59 on March 1 (except on leap years, where dn=60), etc. In this formula dn–3 is used, because in modern times Earth's perihelion ,

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2592-595: The marine sediment . Paleoclimatology is the study of past climates. Proxy data is used in order to relate elements collected in modern-day sedimentary samples to climatic and oceanic conditions in the past. Paleoclimate proxies refer to preserved or fossilized physical markers which serve as substitutes for direct meteorological or ocean measurements. An example of proxies is the use of diatom isotope records of δ13C , δ18O , δ30Si (δ13C diatom , δ18O diatom , and δ30Si diatom ). In 2015, Swann and Snelling used these isotope records to document historic changes in

2673-424: The Sun's surface and are emitted out into space. As a result, the photosphere of the Sun does not emit much X radiation ( solar X-rays ), although it does emit such "hard radiations" as X-rays and even gamma rays during solar flares . The quiet (non-flaring) Sun, including its corona , emits a broad range of wavelengths: X-rays , ultraviolet , visible light , infrared , and radio waves . Different depths in

2754-478: The amount of light penetration, as discussed in pelagic zone . The upper 200 metres is referred to as the photic or euphotic zone. This represents the region where enough light can penetrate to support photosynthesis, and it corresponds to the epipelagic zone. From 200 to 1000 metres lies the dysphotic zone, or the twilight zone (corresponding with the mesopelagic zone). There is still some light at these depths, but not enough to support photosynthesis. Below 1000 metres

2835-505: The attenuating effects of the atmosphere is given by: where c is the atmospheric extinction and m is the relative optical airmass . The atmospheric extinction brings the number of lux down to around 100,000 lux. The total amount of energy received at ground level from the Sun at the zenith depends on the distance to the Sun and thus on the time of year. It is about 3.3% higher than average in January and 3.3% lower in July (see below). If

2916-415: The autotrophs are then broken down, releasing stored solar energy, and giving the heterotroph the energy required for survival. This process is known as cellular respiration . In prehistory , humans began to further extend this process by putting plant and animal materials to other uses. They used animal skins for warmth, for example, or wooden weapons to hunt. These skills allowed humans to harvest more of

2997-422: The brightness of sunlight, many people wear sunglasses . Cars , many helmets and caps are equipped with visors to block the Sun from direct vision when the Sun is at a low angle. Sunshine is often blocked from entering buildings through the use of walls , window blinds , awnings , shutters , curtains , or nearby shade trees . Sunshine exposure is needed biologically for the production of Vitamin D in

3078-445: The change in solar energy in summer and winter. For example, at latitudes of 65 degrees, this can vary by more than 25% as a result of Earth's orbital variation. Because changes in winter and summer tend to offset, the change in the annual average insolation at any given location is near zero, but the redistribution of energy between summer and winter does strongly affect the intensity of seasonal cycles. Such changes associated with

3159-437: The closest approach to the Sun and, therefore, the maximum E ext occurs around January 3 each year. The value of 0.033412 is determined knowing that the ratio between the perihelion (0.98328989 AU) squared and the aphelion (1.01671033 AU) squared should be approximately 0.935338. The solar illuminance constant ( E sc ), is equal to 128×10   lux . The direct normal illuminance ( E dn ), corrected for

3240-881: The core of the Sun is via the very weakly interacting neutrinos . Although the solar corona is a source of extreme ultraviolet and X-ray radiation, these rays make up only a very small amount of the power output of the Sun (see spectrum at right). The spectrum of nearly all solar electromagnetic radiation striking the Earth's atmosphere spans a range of 100  nm to about 1  mm (1,000,000 nm). This band of significant radiation power can be divided into five regions in increasing order of wavelengths : Tables of direct solar radiation on various slopes from 0 to 60 degrees north latitude, in calories per square centimetre, issued in 1972 and published by Pacific Northwest Forest and Range Experiment Station, Forest Service, U.S. Department of Agriculture, Portland, Oregon, USA, appear on

3321-421: The deepest depths. This is why things appear blue underwater. How colours are perceived by the eye depends on the wavelengths of light that are received by the eye. An object appears red to the eye because it reflects red light and absorbs other colours. So the only colour reaching the eye is red. Blue is the only colour of light available at depth underwater, so it is the only colour that can be reflected back to

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3402-443: The direct radiation is not blocked by clouds, it is experienced as sunshine . The warming of the ground (and other objects) depends on the absorption of the electromagnetic radiation in the form of heat . The amount of radiation intercepted by a planetary body varies inversely with the square of the distance between the star and the planet. Earth's orbit and obliquity change with time (over thousands of years), sometimes forming

3483-535: The establishment of globally cooler conditions and the expansion of glaciers across the Northern Hemisphere from 2.73 Ma. While the halocline appears to have prevailed through the late Pliocene and early Quaternary glacial–interglacial cycles , other studies have shown that the stratification boundary may have broken down in the late Quaternary at glacial terminations and during the early part of interglacials. Phytoplankton are restricted to

3564-593: The extraterrestrial solar radiation is 1,367 watts per square meter (the value when the Earth–Sun distance is 1 astronomical unit ), then the direct sunlight at Earth's surface when the Sun is at the zenith is about 1,050 W/m , but the total amount (direct and indirect from the atmosphere) hitting the ground is around 1,120 W/m . In terms of energy, sunlight at Earth's surface is around 52 to 55 percent infrared (above 700 nm ), 42 to 43 percent visible (400 to 700 nm), and 3 to 5 percent ultraviolet (below 400 nm). At

3645-400: The eye, and everything has a blue tinge under water. A red object at depth will not appear red to us because there is no red light available to reflect off of the object. Objects in water will only appear as their real colours near the surface where all wavelengths of light are still available, or if the other wavelengths of light are provided artificially, such as by illuminating the object with

3726-405: The familiar “ROYGBIV”; red, orange, yellow, green, blue, indigo, and violet. Water is very effective at absorbing incoming light, so the amount of light penetrating the ocean declines rapidly (is attenuated) with depth. At one metre depth only 45% of the solar energy that falls on the ocean surface remains. At 10 metres depth only 16% of the light is still present, and only 1% of the original light

3807-435: The integration over the orbital period (also invariant) is a constant. If we assume the solar radiation power  P as a constant over time and the solar irradiation given by the inverse-square law , we obtain also the average insolation as a constant. However, the seasonal and latitudinal distribution and intensity of solar radiation received at Earth's surface does vary. The effect of Sun angle on climate results in

3888-503: The irradiance which can be focused on a surface using mirrors: 48.5 MW/m . The spectrum of the Sun's solar radiation can be compared to that of a black body with a temperature of about 5,800  K (see graph). The Sun emits EM radiation across most of the electromagnetic spectrum . Although the radiation created in the solar core consists mostly of x rays , internal absorption and thermalization convert these super-high-energy photons to lower-energy photons before they reach

3969-564: The late 20th century and in 2000, maerl was extracted at c. 5,000 tonnes per year in Ireland and c. 500,000 tonnes per year in France. Large scale maerl extraction over the past 40 years has removed and degraded maerl beds. In Cornwall, England, maerl has been extracted since the 1970s, but was banned in 2005 by Falmouth Harbour Commissioners. An early reference to maerl was made by John Ray in 1690 who reported it from Falmouth. In Ireland, maerl

4050-458: The light within a specific sensitivity range. Many animals (including humans) have a sensitivity range of approximately 400–700 nm, and given optimal conditions the absorption and scattering by Earth's atmosphere produces illumination that approximates an equal-energy illuminant for most of this range. The useful range for color vision in humans, for example, is approximately 450–650 nm. Aside from effects that arise at sunset and sunrise,

4131-430: The nutricline. Chemical factors include oxygen and trace elements. Biological factors include grazing and migrations. Upwelling carries nutrients from the deep waters into the photic zone, strengthening phytoplankton growth. The remixing and upwelling eventually bring nutrient-rich wastes back into the photic zone. The Ekman transport additionally brings more nutrients to the photic zone. Nutrient pulse frequency affects

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4212-422: The ocean release this, constituting a range of gene families. However this compound can be toxic to humans if swallowed, absorbed through the skin and inhaled. Proteins within plants and animals depend on this compound. Making it a significant part of ecology, it's good to know that it lives in the photic zone as well. [1] Sunlight Sunlight is a portion of the electromagnetic radiation given off by

4293-464: The only listed carcinogens that are known to have health benefits, and a number of public health organizations state that there needs to be a balance between the risks of having too much sunlight or too little. There is a general consensus that sunburn should always be avoided. Epidemiological data shows that people who have more exposure to sunlight have less high blood pressure and cardiovascular-related mortality. While sunlight (and its UV rays) are

4374-448: The open ocean . It also varies with seasonal changes in turbidity, which can be strongly driven by phytoplankton concentrations, such that the depth of the photic zone often decreases as primary production increases. Moreover, the respiration rate is actually greater than the photosynthesis rate. The reason why phytoplankton production is so important is because it plays a prominent role when interwoven with other food webs . Most of

4455-508: The open ocean. Many of these organisms, such as phytoplankton, absorb light in the blue and red range through their photosynthetic pigments, leaving green as the dominant wavelength of reflected light. Therefore the higher the phytoplankton concentration in water, the greener it appears. Small silt particles may also absorb blue light, further shifting the colour of water away from blue when there are high concentrations of suspended particles. The ocean can be divided into depth layers depending on

4536-405: The organisms' activities. Daylighting is the natural lighting of interior spaces by admitting sunlight. Solar irradiance is the solar energy available from sunlight. Researchers can measure the intensity of sunlight using a sunshine recorder , pyranometer , or pyrheliometer . To calculate the amount of sunlight reaching the ground, both the eccentricity of Earth's elliptic orbit and

4617-410: The past 400 years or cosmogenic radionuclides for going back 10,000 years. Such reconstructions have been done. These studies show that in addition to the solar irradiance variation with the solar cycle (the (Schwabe) cycle), the solar activity varies with longer cycles, such as the proposed 88 year (Gleisberg cycle), 208 year (DeVries cycle) and 1,000 year (Eddy cycle). The solar constant

4698-417: The photic zone conditions of the north-west Pacific Ocean , including nutrient supply and the efficiency of the soft-tissue biological pump , from the modern day back to marine isotope stage 5e , which coincides with the last interglacial period . Peaks in opal productivity in the marine isotope stage are associated with the breakdown of the regional halocline stratification and increased nutrient supply to

4779-404: The photic zone, which is approximately two hundred meters deep. This includes phytoplankton (plants), including dinoflagellates , diatoms , cyanobacteria , coccolithophores , and cryptomonads . It also includes zooplankton , the consumers in the photic zone. There are carnivorous meat eaters and herbivorous plant eaters. Next, copepods are the small crustaceans distributed everywhere in

4860-414: The photic zone. The initial development of the halocline and stratified water column has been attributed to the onset of major Northern Hemisphere glaciation at 2.73 Ma, which increased the flux of freshwater to the region, via increased monsoonal rainfall and/or glacial meltwater, and sea surface temperatures . The decrease of abyssal water upwelling associated with this may have contributed to

4941-444: The photic zone. Due to biological uptake, the photic zone has relatively low levels of nutrient concentrations. As a result, phytoplankton doesn't receive enough nutrients when there is high water-column stability. The spatial distribution of organisms can be controlled by a number of factors. Physical factors include: temperature, hydrostatic pressure, turbulent mixing such as the upward turbulent flux of inorganic nitrogen across

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5022-409: The photic zone. Finally, there are nekton (animals that can propel themselves, like fish, squids, and crabs), which are the largest and the most obvious animals in the photic zone, but their quantity is the smallest among all the groups. Phytoplankton are microscopic plants living suspended in the water column that have little or no means of motility. They are primary producers that use solar energy as

5103-420: The photo zone only. As its growth is completely dependent upon photosynthesis. This results in the 50–100 m water level inside the ocean. Growth can also come from land factors, for example minerals that are dissolved from rocks, mineral nutrients from generations of plants and animals ,that made its way into the photic zone. An increase in the amount of phytoplankton also creates an increase in zooplankton,

5184-410: The photosphere have different temperatures, and this partially explains the deviations from a black-body spectrum. There is also a flux of gamma rays from the quiescent sun, obeying a power law between 0.5 and 2.6 TeV . Some gamma rays are caused by cosmic rays interacting with the solar atmosphere, but this does not explain these findings. The only direct signature of the nuclear processes in

5265-407: The phytoplankton competition. Photosynthesis produces more of it. Being the first link in the food chain, what happens to phytoplankton creates a rippling effect for other species. Besides phytoplankton, many other animals also live in this zone and utilize these nutrients. The majority of ocean life occurs in the photic zone, the smallest ocean zone by water volume. The photic zone, although small, has

5346-401: The principal source of illumination is sunlight as mediated by the atmosphere. While the color of the sky is usually determined by Rayleigh scattering , an exception occurs at sunset and twilight. "Preferential absorption of sunlight by ozone over long horizon paths gives the zenith sky its blueness when the sun is near the horizon". The Sun may be said to illuminate , which is a measure of

5427-443: The redistribution of solar energy are considered a likely cause for the coming and going of recent ice ages (see: Milankovitch cycles ). Space-based observations of solar irradiance started in 1978. These measurements show that the solar constant is not constant. It varies on many time scales, including the 11-year sunspot solar cycle. When going further back in time, one has to rely on irradiance reconstructions, using sunspots for

5508-581: The relevant satellite observations indicate a value closer to 1,361 W/m is more realistic. Since 1978, a series of overlapping NASA and ESA satellite experiments have measured total solar irradiance (TSI) – the amount of solar radiation received at the top of Earth's atmosphere – as 1.365 kilo⁠watts per square meter (kW/m ). TSI observations continue with the ACRIMSAT /ACRIM3, SOHO /VIRGO and SORCE /TIM satellite experiments. Observations have revealed variation of TSI on many timescales, including

5589-500: The remnants of ancient plant and animal matter, formed using energy from sunlight and then trapped within Earth for millions of years. The effect of sunlight is relevant to painting , evidenced for instance in works of Édouard Manet and Claude Monet on outdoor scenes and landscapes. Many people find direct sunlight to be too bright for comfort; indeed, looking directly at the Sun can cause long-term vision damage. To compensate for

5670-486: The skin, a vital compound needed to make strong bone and muscle in the body. In many world religions, such as Hinduism , the Sun is considered to be a god , as it is the source of life and energy on Earth. The Sun was also considered to be a god in Ancient Egypt . Sunbathing is a popular leisure activity in which a person sits or lies in direct sunshine. People often sunbathe in comfortable places where there

5751-405: The solar energy reaching the Earth is in the range of visible light, with wavelengths between about 400-700 nm. Each colour of visible light has a unique wavelength, and together they make up white light. The shortest wavelengths are on the violet and ultraviolet end of the spectrum, while the longest wavelengths are at the red and infrared end. In between, the colours of the visible spectrum comprise

5832-491: The solar light it receives. The actual illumination of the surface is about 14,000 lux, comparable to that on Earth "in the daytime with overcast clouds". Sunlight on Mars would be more or less like daylight on Earth during a slightly overcast day, and, as can be seen in the pictures taken by the rovers, there is enough diffuse sky radiation that shadows would not seem particularly dark. Thus, it would give perceptions and "feel" very much like Earth daylight. The spectrum on

5913-592: The solar magnetic cycle and many shorter periodic cycles. TSI provides the energy that drives Earth's climate, so continuation of the TSI time-series database is critical to understanding the role of solar variability in climate change. Since 2003, the SORCE Spectral Irradiance Monitor (SIM) has monitored Spectral solar irradiance (SSI) – the spectral distribution of the TSI. Data indicate that SSI at UV (ultraviolet) wavelength corresponds in

5994-408: The spectral composition changes primarily in respect to how directly sunlight is able to illuminate. When illumination is indirect, Rayleigh scattering in the upper atmosphere will lead blue wavelengths to dominate. Water vapour in the lower atmosphere produces further scattering and ozone, dust and water particles will also absorb particular wavelengths. The existence of nearly all life on Earth

6075-605: The sunlight than was possible through glycolysis alone, and human population began to grow. During the Neolithic Revolution , the domestication of plants and animals further increased human access to solar energy. Fields devoted to crops were enriched by inedible plant matter, providing sugars and nutrients for future harvests. Animals that had previously provided humans with only meat and tools once they were killed were now used for labour throughout their lives, fueled by grasses inedible to humans. Fossil fuels are

6156-486: The surface is slightly redder than that on Earth, due to scattering by reddish dust in the Martian atmosphere. For comparison, sunlight on Saturn is slightly brighter than Earth sunlight at the average sunset or sunrise. Even on Pluto, the sunlight would still be bright enough to almost match the average living room. To see sunlight as dim as full moonlight on Earth, a distance of about 500 AU (~69  light-hours )

6237-440: The surface of the Sun. A photon starting at the center of the Sun and changing direction every time it encounters a charged particle would take between 10,000 and 170,000 years to get to the surface. Sunlight is a key factor in photosynthesis , the process used by plants and other autotrophic organisms to convert light energy , normally from the Sun, into chemical energy that can be used to synthesize carbohydrates and fuel

6318-474: The timing of melatonin synthesis, maintenance of normal circadian rhythms , and reduced risk of seasonal affective disorder . Long-term sunlight exposure is known to be associated with the development of skin cancer , skin aging , immune suppression , and eye diseases such as cataracts and macular degeneration . Short-term overexposure is the cause of sunburn , snow blindness , and solar retinopathy . UV rays, and therefore sunlight and sunlamps, are

6399-430: The top of the atmosphere, sunlight is about 30% more intense, having about 8% ultraviolet (UV), with most of the extra UV consisting of biologically damaging short-wave ultraviolet. Direct sunlight has a luminous efficacy of about 93  lumens per watt of radiant flux . This is higher than the efficacy (of source) of artificial lighting other than LEDs , which means using sunlight for illumination heats up

6480-535: The web. Different bodies of the Solar System receive light of an intensity inversely proportional to the square of their distance from Sun. A table comparing the amount of solar radiation received by each planet in the Solar System at the top of its atmosphere: The actual brightness of sunlight that would be observed at the surface also depends on the presence and composition of an atmosphere . For example, Venus's thick atmosphere reflects more than 60% of

6561-410: The zooplankton feeds on the phytoplankton as they are at the bottom of the food chain. Dimethylsulfide loss within the photic zone is controlled by microbial uptake and photochemical degradation. But what exactly is dimethylsulfide and why is it important? This compound (see the photo) helps regulate sulfur cycle and ecology within the ocean. Marine bacteria, algae, coral and most other organisms within

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