sun safety

Sun give us heat,light and fire.We all need some sun exposure; it's our primary source of vitamin D, which helps us absorb calcium for stronger, healthier bones. But it doesn't take much time in the sun for most people to get the vitamin D they need, and repeated unprotected exposure to the sun's ultraviolet rays can cause skin damage, eye damage, immune system suppression, and skin cancer. Even people in their twenties can develop skin cancer.



Most kids rack up a lot of their lifetime sun exposure before age 18, so it's important that parents teach their children how to enjoy fun in the sun safely. With the right precautions, you can greatly reduce your child's chance of developing skin cancer.


source:http://kidshealth.org/parent/firstaid_safe/outdoor/sun_safety.html

about the sunlight

Sunlight, in the broad sense, is the total frequency spectrum of electromagnetic radiation given off by the Sun, particularly infrared, visible, andultraviolet light. On Earth, sunlight is filtered through the Earth's atmosphere, and solar radiation is obvious as daylight when the Sun is above thehorizon.

When the direct solar radiation is not blocked by clouds, it is experienced as sunshine, a combination of bright light and radiant heat. When it is blocked by the clouds or reflects off of other objects, it is experienced as diffused light.

The World Meteorological Organization uses the term "sunshine duration" to mean the cumulative time during which an area receives directirradiance from the Sun of at least 120 watts per square meter.

Sunlight may be recorded using a sunshine recorder, pyranometer or pyrheliometer. Sunlight takes about 8.3 minutes to reach the Earth.

On average, it takes energy between 10,000 and 170,000 years to leave the sun's interior and then be emitted from the surface as light.

Direct sunlight has a luminous efficacy of about 93 lumens per watt of radiant flux. Bright sunlight provides illuminance of approximately 100,000 luxor lumens per square meter at the Earth's surface.

Sunlight is a key factor in photosynthesis, a process vital for many living beings on Earth.

source:http://en.wikipedia.org/wiki/Sunlight

view of the sun

Sunlight can be used for growth, maintenance and for destruction. It can be used for growing plants, maintaining our population through rice and other food crops and destroys bacteria and virus in the environment.

source:http://answers.yahoo.com/question/index?qid=20070520063024AAsK28S

Observation and effects

-The brightness of the sun can cause pain from looking at it with the naked eye, although doing so for brief periods is not hazardous for normal, non-dilated eyes.
- Looking directly at the Sun causes phosphene visual artifacts and temporary partial blindnes
-Long-duration viewing of the direct Sun with the naked eye can begin to cause UV-induced, sunburn-like lesions on the retina after about 100 seconds, particularly under conditions where the UV light from the Sun is intense and well focused
-Viewing the Sun through light-concentrating optics such as binoculars may result in permanent damage to the retina without an appropriate filter that blocks UV and substantially dims the sunlight. 
- Unfiltered binoculars can deliver over 500 times as much energy to the retina as using the naked eye, killing retinal cells almost instantly.
-Even brief glances at the midday Sun through unfiltered binoculars can cause permanent blindness.[citation needed]
-Partial solar eclipses are hazardous to view because the eye's pupil is not adapted to the unusually high visual contrast: the pupil dilates according to the total amount of light in the field of view, not by the brightest object in the field. 
-During partial eclipses most sunlight is blocked by the Moon passing in front of the Sun, but the uncovered parts of the photosphere have the same surface brightness as during a normal day.
- In the overall gloom, the pupil expands from ~2 mm to ~6 mm, and each retinal cell exposed to the solar image receives about ten times more light than it would looking at the non-eclipsed Sun. 
-The hazard is insidious for inexperienced observers and for children, because there is no perception of pain: it is not immediately obvious that one's vision is being destroyed.
-During sunrise and sunset sunlight is attenuated due to Rayleigh scattering and Mie scattering from a particularly long passage through Earth's atmosphere.
- Sun is sometimes faint enough to be viewed comfortably with the naked eye or safely with optics (provided there is no risk of bright sunlight suddenly appearing through a break between clouds). Hazy conditions, atmospheric dust, and high humidity contribute to this atmospheric attenuation.


credit:http://en.wikipedia.org/wiki/Sun#Observation_and_effects

Energy from the sun

Architecture and urban planning
agriculture and horticulture
Solar lighting
Solar thermal
Water heating
Heating, cooling and ventilation
Water treatment
Cooking
Process heat
Solar power
Concentrated solar power
Photovoltaics
Solar vehicles


credit:http://en.wikipedia.org/wiki/Solar_energy#Energy_from_the_Sun

Applications of solar technology

Solar energy refers primarily to the use of solar radiation for practical ends. However, all renewable energies, other than geothermal and tidal, derive their energy from the sun.
Solar technologies are broadly characterized as either passive or active depending on the way they capture, convert and distribute sunlight. Active solar techniques use photovoltaic panels, pumps, and fans to convert sunlight into useful outputs. Passive solar techniques include selecting materials with favorable thermal properties, designing spaces that naturally circulate air, and referencing the position of a building to the Sun. Active solar technologies increase the supply of energy and are considered supply side technologies, while passive solar technologies reduce the need for alternate resources and are generally considered demand side technologies.

credit:http://en.wikipedia.org/wiki/Solar_energy#Energy_from_the_Sun

the sun and its energy

The sun's energy is the primary source of energy for all surface phenomena and life on Earth. Combined with the material of the Earth (including the molecules held close by the Earth's gravitational force called the atmosphere), this energy provides for the immense diversity of life forms that are found on the Earth. We will now look in detail at solar energy and its interplay with the constituents of the Earth's atmosphere.


credit:http://telstar.ote.cmu.edu/environ/m3/s2/02sun.shtml

The Sun’s Energy is in Many Things

The energy from the sun makes rain fall and wind blow. We can capture that energy with dams
and windmills.
Coal, oil, and natural gas were made from prehistoric plants and animals. The energy in them
came from the sun. We use that energy to cook our food, warm our houses, run our cars, and
make electricity

credit:http://www.need.org/needpdf/infobook_activities/ElemInfo/SolarE.pdf

Sunlight

Sunlight is Earth's primary source of energy. 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.

credit:http://en.wikipedia.org/wiki/Sun

Sunlight

credit:http://en.wikipedia.org/wiki/Sun

Name and etymology

The English proper noun Sun developed from Old English sunne (around 725, attested in Beowulf), and may be related to south. Cognates to English sun appear in other Germanic languages, including Old Frisian sunne, sonne ("sun"), Old Saxon sunna, Middle Dutch sonne, modern Dutch zon, Old High German sunna, modern German Sonne, Old Norse sunna, and Gothic sunnō. All Germanic terms for the Sun stem from Proto-Germanic *sunnōn.
In relation, the Sun is personified as a goddess in Germanic paganism; Sól/Sunna.Scholars theorize that the Sun, as Germanic goddess, may represent an extension of an earlier Proto-Indo-European sun deity due to Indo-European linguistic connections between Old Norse Sól, Sanskrit Surya, Gaulish Sulis, Lithuanian Saulė, and Slavic Solnitse.
The English weekday name Sunday is attested in Old English (Sunnandæg; "Sun's day", from before 700) and is ultimately a result of a Germanic interpretation of Latin dies solis, itself a translation of the Greek heméra helíou. The Latin name for the star, Sol, is widely known but is not common in general English language use; the adjectival form is the related word solar. The term sol is also used by planetary astronomers to refer to the duration of a solar day on another planet, such as Mars.A mean Earth solar day is approximately 24 hours, while a mean Martian 'sol' is 24 hours, 39 minutes, and 35.244 seconds.


credit:http://en.wikipedia.org/wiki/Sun

sun

The Sun is the brightest and most familiar object in the sky. Life on Earth would not be possible without it:

The food we eat exists because of sunlight falling on green plants, and the fuel we burn comes either from such plants, or was accumulated by them (in the forms of coal, oil and natural gas) long ago.

The Earth would probably not be fit for life. Life as we know it needs liquid water, and Earth is the only planet to have it: without the Sun, Earth would be an icy rock in space. Even now, Earth is probably the only place in our solar system fit for life: any water on Venus and Mercury would become steam, any on Mars or on more distant planets would freeze.

credit:http://www-spof.gsfc.nasa.gov/stargaze/Sun1lite.htm

Sunlight is created

The Sun has no sharply defined surface like that of the Earth, because it is too hot to be anything but gas. Rather, what appears to us as the surface is a layer in the Sun's atmosphere, the "photosphere" (sphere of light) which emits light ("radiates") because ot its high temperature.
All hot substances radiate light, either the visible kind or beyond the rainbow spectrum, in the "infra red" (IR; "below red") and "ultra violet" (UV; "above violet") ranges. This glow [called "black body radiation" by physicists--the glow of a body with no color of its own] is the way a red-hot piece of iron or the filament in an electric light bulb produce light. The hotter the object, the brighter it shines, and the further away from red is its color. Conversely, the color of a hot object (if it is dense) tells us how hot it is. In the case of the Sun, the color of the photosphere suggests a temperature of 5780 degrees Kelvin (degrees Celsius measured from the absolute zero, about 5500° C.)



credit:http://www-spof.gsfc.nasa.gov/stargaze/Sun1lite.htm

Effect on human health

The body produces vitamin D from sunlight (specifically from the UVB band of ultraviolet light), and excessive seclusion from the sun can lead to deficiency unless adequate amounts are obtained through diet.

Sunburn can have mild to severe inflammation effects on skin; this can be avoided by using a proper sunscreen cream or lotion or by gradually building up melanocytes with increasing exposure. Another detrimental effect of UV exposure is accelerated skin aging (also called skin photodamage), which produces a difficult to treat cosmetic effect. Some people are concerned that ozone depletion is increasing the incidence of such health hazards. A 10% decrease in ozone could cause a 25% increase in skin cancer.^[19]

A lack of sunlight, on the other hand, is considered one of the primary causes of seasonal affective disorder (SAD), a serious form of the "winter blues". SAD occurrence is more prevalent in locations further from the tropics, and most of the treatments (other than prescription drugs) involve light therapy, replicating sunlight via lamps tuned to specific wavelengths of visible light, or full-spectrum bulbs.A recent study indicates that more exposure to sunshine early in a person’s life relates to less risk from multiple sclerosis (MS) later in life

credit:http://en.wikipedia.org/wiki/Sunlight

Sunlight

Sunlight, in the broad sense, is the total frequency spectrum of electromagnetic radiation given off by the Sun, particularly infrared, visible, andultraviolet light. On Earth, sunlight is filtered through the Earth's atmosphere, and solar radiation is obvious as daylight when the Sun is above thehorizon.

When the direct solar radiation is not blocked by clouds, it is experienced as sunshine, a combination of bright light and radiant heat. When it is blocked by the clouds or reflects off of other objects, it is experienced as diffused light.

The World Meteorological Organization uses the term "sunshine duration" to mean the cumulative time during which an area receives directirradiance from the Sun of at least 120 watts per square meter.^[1]

Sunlight may be recorded using a sunshine recorder, pyranometer or pyrheliometer. Sunlight takes about 8.3 minutes to reach the Earth.

On average, it takes energy between 10,000 and 170,000 years to leave the sun's interior and then be emitted from the surface as light.^[2]Direct sunlight has a luminous efficacy of about 93 lumens per watt of radiant flux. Bright sunlight provides illuminance of approximately 100,000 luxor lumens per square meter at the Earth's surface.

credit:http://en.wikipedia.org/wiki/Sunlight