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#451 2019-07-10 00:34:42

ganesh
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Registered: 2005-06-28
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Re: Miscellany

371) Tiger

Tigers: The Largest Cats in the World

Tigers are iconic creatures, and the largest felines in the world.

Tigers are the largest felines in the world and as such, many cultures consider the tiger to be a symbol of strength, courage and dignity. The tiger is one of the twelve Chinese zodiac animals, and those born in the "Year of the Tiger" are thought to be brave, competitive and self-confident.

However, because hunting them is also a sign of bravery in some cultures, tigers are endangered. Tigers are hunted for their meat, pelt and body parts that are used in folk remedies. To make matters worse, these great cats have lost most of their habitat due to logging, road building and development, according to All About Wildlife. Experts estimate there are no more than 3,200 tigers left in the wild.

Do all tigers have stripes?

Most tigers have the characteristic orange fur with black or brown stripes, but these markings vary between subspecies. For example, the very large Siberian tiger has pale orange fur with few stripes, while the smaller Sumatran tigers in the Sunda Islands have dark, thickly striped fur.

No two tigers have the same markings, and their stripes are as individual as fingerprints are for humans. In the wild, a tiger's stripes are important for survival, as they act as camouflage, appearing as moving shadows in long grass and in trees, according to National Geographic.

The white Bengal tigers seen in some zoos are the result of a recessive gene, and are not albinos. In fact, it's unlikely that true albino tigers (with pink eyes) exist. Some historical reports detail tigers with black fur and tan stripes, caused by excessive pigmentation, but these accounts are extremely rare.

On the backs of each ear, tigers have a white spot of fur, called ocelli, according to Tigers.org. It's likely the spots act as fake eyes and they may also help tigers communicate with one another.

A tiger's hind legs are longer than its front legs, allowing it to jump up to 32.5 feet (10 meters), according to Sea World. Tiger claws are up to 4 inches (10 centimeters) long, and are used to grab and hold onto their prey.

The largest tiger subspecies, the Siberian, also called Amur, are 10.75 feet (3.3 m) long and weigh up to 660 pounds (300 kilograms), according to National Geographic. The smallest tiger is the Sumatran, which weighs 165 - 308 pounds (74 - 139 kg), according to the World Wildlife Fund(WWF). Tigers also have very long tails, which can add around 3 feet (one m) to their overall length, according to Sea World.

Adorable Tiger Cubs Aren't So Great at Walking

Where tigers live and what they eat

Wild tigers live in Asia. Larger subspecies, such as the Siberian tiger, tend to live in northern, colder areas, such as eastern Russia and northeastern China. Smaller subspecies live in southern, warmer countries, such as India, Bangladesh, Nepal, Bhutan, Myanmar, Laos, Cambodia, Vietnam, Malaysia and Indonesia.
Depending on the subspecies, tigers live in a variety of environments, including arid forests, flooded mangrove forests, tropical forests and taiga (a cold forest with coniferous trees), according to the San Diego Zoo.

All tigers are carnivores. Most of a tiger's diet consists of large prey, such as pigs, deer, rhinos or elephant calves. To kill their prey, tigers clamp down on the animal's neck with their jaws and suffocate the animal. The tiger's canine teeth have pressure-sensing nerves, so it knows exactly where to deliver a fatal bite to its prey, according to the WWF. Though tigers are fierce hunters, they are no strangers to failure, as they are successful in only 10% of their hunts, according to National Geographic.

The tiger life

Tigers are solitary creatures; they like to spend most of their time alone, roaming their massive territories looking for food. According to the San Diego Zoo, the Siberian tiger has the largest range; its territory spans more than 4,000 square miles (10,000 square km). Tigers mark their territory by spraying a mix of urine and scent gland secretions onto trees and rocks. They also scratch marks into trees with their claws.

Tiger babies are born helpless. At birth, a cub weighs 2.2 pounds (1 kg), and a female may have as many as seven cubs at a time, according to the San Diego Zoo. Around half of all cubs don't live beyond the age of two, according to WWF. The mother must leave the cubs while she hunts, leaving them open to other predators. Most tiger mothers are unable to kill enough prey to feed a large litter, so some cubs may die of starvation.

At just 8 weeks old, tiger cubs are ready to learn how to hunt and go out on hunting expeditions with their mother. At 2 years old, the cubs will set out on their own, and their mother will be ready for another set of cubs. In the wild, tigers typically live 10 to 15 years, according to Smithsonian's National Zoo.

Classification/taxonomy

For many years, scientists classified tigers into nine subspecies: six living subspecies and three extinct ones. But in recent years, some researchers have challenged the traditional classification. A 2015 study published in the journal Science Advances argued that there are only two subspecies of tigers.

However, a study published in the journal Current Biology in 2018 presented genomic evidence supporting six genetically distinct subspecies of tigers:the Bengal tiger (Panthera tigris tigris), the Amur tiger (P.t. altaica), the South China tiger (P.t. amoyensis), the Sumatran tiger (P.t. sumatrae), the Indochinese tiger (P.t. corbetti), and the Malayan tiger (P.t. jacksoni).

The Javan tiger was last recorded in the 1970s, the Caspian tiger was lost in the 1950s, and the Bali tiger became extinct in the 1930s, according to Panthera, a wild-cat conservation organization.

Conservation status

There are more tigers in captivity than there are in the wild. According to the WWF, there are about 5,000 captive tigers in the United States alone, but there are fewer than 3,200 tigers in the wild.

The International Union for the Conservation of Nature's (IUCN's) Red List of Threatened Species categorizes the Amur/Siberian, Indochinese and Bengal tigers as endangered, and the Sumatran, Malayan and South ChinaTigers as critically endangered. Most remaining tigers live on wildlife refuges to protect them from poachers.

Poaching is by far the biggest threat facing tigers today. Illegal demand for tiger bones (used in tonics and medicines), tiger skin (seen as a status symbol) and other body parts, is driving the killing and trafficking, which has had an overwhelming impact on tiger populations and resulted in localized extinctions, according to Save Wild Tigers. The continued demand for tiger parts is pushing the species closer and closer to extinction.

In addition to the threat of poaching, only 7% of the tiger's original range remains due to human agriculture, logging, settlements and roads.


It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi. 

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

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#452 2019-07-11 15:50:44

Monox D. I-Fly
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From: Indonesia
Registered: 2015-12-02
Posts: 1,675

Re: Miscellany

ganesh wrote:

For many years, scientists classified tigers into nine subspecies: six living subspecies and three extinct ones.

Saber-toothed tiger, Smilodon, and...?


Actually I never watch Star Wars and not interested in it anyway, but I choose a Yoda card as my avatar in honor of our great friend  who has passed away. May his adventurous soul rest in peace at heaven.

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#453 2019-07-11 16:08:36

ganesh
Administrator
Registered: 2005-06-28
Posts: 28,455

Re: Miscellany

Monox D. I-Fly wrote:
ganesh wrote:

For many years, scientists classified tigers into nine subspecies: six living subspecies and three extinct ones.

Saber-toothed tiger, Smilodon, and...?

I think they were : The Bali Tiger (Panthera tigris balica), The Caspian Tiger (Panthera tigris virgata), and The Javan Tiger (Panthera tigris sondaica).


It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi. 

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

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#454 2019-07-12 19:01:50

Monox D. I-Fly
Member
From: Indonesia
Registered: 2015-12-02
Posts: 1,675

Re: Miscellany

ganesh wrote:
Monox D. I-Fly wrote:
ganesh wrote:

For many years, scientists classified tigers into nine subspecies: six living subspecies and three extinct ones.

Saber-toothed tiger, Smilodon, and...?

I think they were : The Bali Tiger (Panthera tigris balica), The Caspian Tiger (Panthera tigris virgata), and The Javan Tiger (Panthera tigris sondaica).

I... forgot that "extinct" doesn't always mean "prehistoric". Silly me.


Actually I never watch Star Wars and not interested in it anyway, but I choose a Yoda card as my avatar in honor of our great friend  who has passed away. May his adventurous soul rest in peace at heaven.

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#455 2019-07-13 00:16:59

ganesh
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Registered: 2005-06-28
Posts: 28,455

Re: Miscellany

372) Death Valley

Death Valley, structural depression primarily in Inyo county, southeastern California, U.S. It is the lowest, hottest, and driest portion of the North American continent. Death Valley is about 140 miles (225 km) long, trends roughly north-south, and is from 5 to 15 miles (8 to 24 km) wide. The valley is bounded on the west by the Panamint Range and on the east by the Black, Funeral, and Grapevine mountains of the Amargosa Range. It lies near the undefined border between the Great Basin and the Mojave Desert.

Geologically, Death Valley forms part of the southwestern portion of the Great Basin. It is similar to other structural basins of the region but is unique in its depth. Portions of the great salt pan that forms part of the floor of the valley are the lowest land areas of the Americas. About 550 square miles (1,425 square km) of the valley’s floor lie below sea level. A point in Badwater Basin, lying 282 feet (86 metres) below sea level, is the lowest area in North America. Less than 20 miles (30 km) west is the 11,049-foot (3,368-metre) Telescope Peak, the area’s highest point. Death Valley was an obstacle to movements of pioneer settlers (whence its name was derived) and later was a centre of borax exploitation; its extreme environment now attracts tourists and scientists.

Physical Environment

For a short time after its christening in 1849 by a hapless party of emigrants who endured intense suffering while crossing it, Death Valley was little known except to Native Americans (primarily Shoshone) of the area and to prospectors searching the surrounding mountains. The first scientific notice of the valley seems to have been a brief mention published in 1868 by a California state geologist. The area remained seldom visited until the 1870s, when gold and silver were discovered in the surrounding mountains, and 1880s, when boraxdeposits were found in the valley. Borax production, notably at the Harmony Borax Works (1883–88), gave rise to the famous 20-mule team wagons, which hauled the product to Mojave, California. Several ghost towns are located around the valley, and some still contain ruined buildings. They sprang up from the late 19th to the early 20th century following gold, copper, and silver strikes in the area. Deserted when the mines were depleted, each existed for only a few years. For example, Rhyolite, founded in 1904, was a gold-mining boomtown of 10,000 people with its own stock exchange, electric plant, and opera; in 1911 the main mine was closed, and the town was deserted by 1916.

The geologic history of Death Valley is extremely complex and involves different types of fault activity at various periods, in addition to crustal sinking and even some volcanic activity. Essentially, Death Valley is a graben, or rift valley, formed by the sinking of a tremendous expanse of rock lying between parallel uplifted, tilted-block mountain ranges to the east and west. A type of fault activity called block faulting, in which the movement is predominantly vertical, began to form the valley about 30 million years ago. As crustal blocks sank, they formed the great trough of the valley, and other blocks were uplifted to gradually form the adjacent mountain ranges. As the valley sank, it was filled by sediments that were eroded from the surrounding hills; in the central part of the valley the bedrock floor is buried beneath as much as 9,000 feet (2,745 metres) of sediment. The valley floor has continued to tilt and sink.

The floor of Death Valley is noted for its extremes of temperature and aridity. A record world and North American high shaded air temperature of 134 °F (57 °C) was recorded in 1913, and summer temperatures often exceed 120 °F (49 °C). The hottest summer on record in the valley (1996) saw temperatures top 120 °F on 40 days. Ground temperatures as high as 201 °F (94 °C) have been reported. The high temperatures and low humidity contribute to an exceptionally high evaporation rate.
Winter minimum temperatures rarely fall to the freezing point; the record lowest temperature was 15 °F (−9 °C). Most rainfall is blocked by the mountains to the west, so the valley is extremely arid. In a 50-year period in the 20th century, the average annual rainfall at Furnace Creek was only 1.66 inches (42.2 mm), the maximum annual rainfall was 4.5 inches (114.3 mm), and two years passed with no measurable rainfall.

Most of the surface water in Death Valley is in the saline ponds and marshes around the salt pan. The Amargosa River brings some water into the southern end of the valley from desert areas to the east, but most of its flow is underground. Salt Creek, draining the northern arm of the valley, also has only short stretches of perennial surface flow.

At times in the past, much more water reached Death Valley. During the Wisconsin Glacial Stage of the Pleistocene Epoch, perhaps about 50,000 years ago, a body of water (Lake Manly) filled the valley to a depth of as much as 600 feet (180 metres). More recently, some 2,000 to 5,000 years ago, a shallow lake occupied the floor of the valley, its evaporation producing the present salt pan.

Plant And Animal Life

Lack of water makes Death Valley a desert, but it is by no means devoid of life. Plant life above the microscopic level is absent from the salt pan, but salt-tolerant pickleweed, salt grass, and rushes grow around the springs and marshes at its edges. Introduced tamarisks provide shade around some of the springs and in the inhabited areas at Furnace Creek, but, because they crowd out native vegetation, eradication efforts are ongoing. Mesquite flourishes where less-saline water is available. Creosote bush dominates the gravel fan surfaces around most of the valley, giving way to desert holly at the lowest elevations. Cactus is rare in the lowest part of the valley but abundant on the fans farther north. Higher elevations support juniper and piñon pine. Spring rains bring out a great variety of desert wildflowers.

Animal life is varied, although nocturnal habits conceal many of the animals from visitors to the valley. Rabbits and several types of rodents, including antelope ground squirrels, kangaroo rats, and desert wood rats, are present and are the prey of coyotes, kit foxes, and bobcats. The largest native mammal in the area, and perhaps the best-studied member of the fauna, is the desert bighorn. Small herds of these sheep are most commonly found in the mountains surrounding Death Valley, but they occasionally visit the valley floor. Wild burros, descendants of animals lost or abandoned by prospectors and miners, became so numerous as to threaten, through overgrazing, the natural vegetation on which other animals depend. Burro removal began in the 1960s, and live-capture efforts were subsequently attempted in hopes of eliminating the population.

Though it may seem that the only birds present are the raucous and numerous ravens, the first biological survey of the valley, in the 1890s, reported 78 species of birds. More than three times that number are now known to inhabit or visit the area, the roadrunner being a particularly well-known resident. Lizards, snakes (including rattlesnakes such as sidewinders), and scorpions are common. Even native fish are to be found in Death Valley. Several species of pupfish of the genus Cyprinodon live in Salt Creek and other permanent bodies of water; the highly endangered Devils Hole pupfish (C. diabolis) lives in a single desert pool.

Death Valley National Park

Death Valley National Park covers some 5,270 square miles (13,650 square km) of the valley, primarily in California. Much of the park’s northeastern border is the Nevada state line, but a small portion extends into Nevada’s Bullfrog Hills. Inyo National Forest and the Inyo Mountains border it to the west, the Panamint Valley and the Slate Range lie to the southwest, and the U.S. Army’s Fort Irwin and the National Training Center adjoin it to the south. The Amargosa River and the Greenwater Range constitute parts of the southeastern border. Death Valley was originally designated a national monument in 1933 and made a national park in 1994. Today’s national park covers considerably more area than the original national monument. The national monument was expanded several times, including in 1937 and in 1952, when Devils Hole, located in Nevada’s Ash Meadows National Wildlife Refuge, was added. In 1994 the California Desert Protection Act added more than 2,000 square miles (5,100 square km) and redesignated it a national park, the largest in the 48 conterminous U.S. states.

The park contains a number of unique landforms. The five dune areas include the 680-foot- (205-metre-) high Eureka Sand Dunes, California’s tallest. The northern section of the park is dotted with volcanic craters such as Ubehebe Crater, 700 feet (215 metres) deep and 0.5 mile (0.8 km) wide. At Racetrack Playa, rocks as large as 700 pounds (320 kg) leave trails as they mysteriously slide across a flat area; they are probably blown by wind when precipitationcreates a moist, slippery clay surface. Other attractions include Scotty’s Castle, a mansion built in the 1920s by Chicago businessman Albert Johnson and named for his prospector friend Walter Scott, a spinner of tall tales known as “Death Valley Scotty.” Artist’s Drive is an 8-mile (13-km) loop through colourful mountains and canyons. Jagged pinnacles of salt form on the salt pan at Devil’s Golf Course. The main visitor centre is at Furnace Creek in the central part of the park and includes exhibits on history, geology, and nature; a second visitor centre is at Beatty, Nevada, outside the park’s eastern boundary. Nearby attractions include Kings Canyon and Sequoia national parks, Manzanar National Historic Site, and Mojave National Preserve.


It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi. 

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

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#456 2019-07-15 00:53:13

ganesh
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Registered: 2005-06-28
Posts: 28,455

Re: Miscellany

373) Snake gourd

Snake gourd, (Trichosanthes cucumerina), also called serpent gourd, rapid-growing vine of the gourd family (Cucurbitaceae), cultivated for its oddly shaped edible fruits. The snake gourd is native to southeastern Asia and Australia and is also grown in parts of tropical Africa. The whole fruit is eaten as a vegetable when young and can be dried and used as a soap. The leaves and shoots are also edible, and the pulp of mature fruits is sometimes eaten as a tomato substitute.

The snake gourd is an annual plant with forked tendrils and kidney- or heart-shaped leaves that are sometimes palmately lobed. The white unisexual flowers have long lacy fringes on the five petals and open at night. The narrow fruits often reach 1.5 metres (5 feet) in length; they are green with white stripes when young, becoming a red-orange colour when mature.

The important health benefits of snake gourd include its ability to reduce fever, detoxify the body, improve digestion, increase hydration, strengthen the immune system, manages diabetes, improve strength and quality of the hair, and aid in weight loss.

What is Snake Gourd?

Snake gourd is a vine plant that climbs up a tree and then unfurls its flowers and fruits to hang down to the ground. Some of the largest specimens can grow up to five feet in length, which is why this gourd is often used to make the traditional Australian musical instrument, the didgeridoo. This plant is native to Southeast Asia, including Myanmar, India, Indonesia, Sri Lanka, and other neighboring countries, as well as some parts of Australia and Africa. It may not be a type of vegetable that is well-known around the world, but certain cultures have been utilizing this unique food variety for hundreds, and perhaps thousands, of years.

The taste is bitter, but this often disappears when cooking, although once the vegetable is ripe, the bitterness is more difficult to eliminate. The leaves, tendrils, and other leafy parts of the plant are often used as vegetable greens, while the fleshy meat often replaces tomatoes in terms of culinary applications.

It is strange in appearance, name, and taste, but its health benefits cannot be denied. Let’s take a closer look at what specifically makes snake gourd such an important dietary staple in so many cultures around the world.

Snake Gourd Nutrition Facts

Snake gourd contains a rich variety of nutrients, vitamins, and minerals that are essential for human health, including significant levels of dietary fiber, a small number of calories, and high levels of protein.  In terms of vitamins, it possesses vitamin A, B, C, as well as manganese, magnesium, calcium, iron, potassium, and iodine.

Health Benefits of Snake Gourd

Health benefits of snake gourd include the following:

Reduces Fever

In many tropical countries, fever can be a major danger to public health, regardless of its cause. Snake gourd can be turned into a decoction and given to people suffering from fever.  Overnight, fevers tend to break and the natural healing process can begin.

Detoxifies the Body

Snake gourd has been used as a diuretic in traditional medicine for many years, as it stimulates the liver and increases urination, thereby speeding up the elimination of toxins from the body.  It increases the creation of bodily fluids, which can eliminate dryness and dehydration, and help in the normal functioning of the kidneys and bladder. Juice from the leaves can also stimulate vomiting in case something toxic has been consumed.

Treats Digestive Issues

Children with bowel problems have been given snake gourd to ease their discomfort, as it acts as a mild laxative. Furthermore, the high fibercontent of snake gourd can help anyone with bowel disorders and can eliminate constipation, reduce cramping and bloating, and optimize the nutrient absorption process in the body.

Improves Respiratory System

Snake gourd functions as an expectorant, loosening pus and phlegm in the sinuses and respiratory tracts so that they can be eliminated.  This further benefits the immune system, as toxins and other foreign agents often get caught in phlegm and mucus to cause more serious conditions.

Hair Care

For people suffering from alopecia, snake gourd is said to stimulate the growth of new hair and protect weakening follicles from hair loss.  This can be attributed to its rich mineral and vitamin content, particularly its high level of carotenes, which specifically care for the skin and hair. It is also claimed that snake gourd can reduce the frequency and intensity of dandruff.

Boosts Immune System

Some research has shown snake gourd to have antibiotic properties, and when combined with the levels of antioxidant carotenes and vitamin C found in the vegetable, this helpful gourd can significantly boost overall health.  The specifics of what conditions the antibiotic effects are most useful for is still a subject of research.

Manages Diabetes

The low-calorie, high-nutrient composition of snake gourd makes it a favorite anti-diabetic food source, and can also lessen the effects if the condition already exists.  Obesity is one of the major signals of oncoming diabetes, and snake gourd functions as a great dietary option due to its effect of making you feel sated and satisfied without adding many excess calories.

Relieves Stress

In traditional medicine, snake gourd was often utilized to reduce heart palpitations and ease the nervous system to induce lower blood pressure.  This is likely due to the presence of potassium in the vegetable, which acts as a vasodilator and reduces stress on the cardiovascular system.


It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi. 

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

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#457 Yesterday 14:40:30

Monox D. I-Fly
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From: Indonesia
Registered: 2015-12-02
Posts: 1,675

Re: Miscellany

ganesh wrote:

This plant is native to Southeast Asia, including Myanmar, India, Indonesia, Sri Lanka, and other neighboring countries, as well as some parts of Australia and Africa.

Yes, this plant is often used for ornaments at city parks in my country (and maybe your country as well, assuming you are from India). It's beautiful and relaxing when you're under it, until one day I looked up to the leaves and noticed a hanging spherical web containing multiple wiggling maggots. It gave me goosebumps and made me immediately left.


Actually I never watch Star Wars and not interested in it anyway, but I choose a Yoda card as my avatar in honor of our great friend  who has passed away. May his adventurous soul rest in peace at heaven.

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#458 Yesterday 16:11:46

ganesh
Administrator
Registered: 2005-06-28
Posts: 28,455

Re: Miscellany

Monox D. I-Fly wrote:
ganesh wrote:

This plant is native to Southeast Asia, including Myanmar, India, Indonesia, Sri Lanka, and other neighboring countries, as well as some parts of Australia and Africa.

Yes, this plant is often used for ornaments at city parks in my country (and maybe your country as well, assuming you are from India). It's beautiful and relaxing when you're under it, until one day I looked up to the leaves and noticed a hanging spherical web containing multiple wiggling maggots. It gave me goosebumps and made me immediately left.

Oh.....


It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi. 

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

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#459 Today 00:26:42

ganesh
Administrator
Registered: 2005-06-28
Posts: 28,455

Re: Miscellany

374) Solar energy

Solar energy, radiation from the Sun capable of producing heat, causing chemical reactions, or generating electricity. The total amount of solar energy incident on Earth is vastly in excess of the world’s current and anticipated energy requirements. If suitably harnessed, this highly diffused source has the potential to satisfy all future energy needs. In the 21st century solar energy is expected to become increasingly attractive as a renewable energy source because of its inexhaustible supply and its nonpolluting character, in stark contrast to the finite fossil fuels coal, petroleum, and natural gas.

The Sun is an extremely powerful energy source, and sunlight is by far the largest source of energy received by Earth, but its intensity at Earth’s surface is actually quite low. This is essentially because of the enormous radial spreading of radiation from the distant Sun. A relatively minor additional loss is due to Earth’s atmosphere and clouds, which absorb or scatter as much as 54 percent of the incoming sunlight. The sunlight that reaches the ground consists of nearly 50 percent visible light, 45 percent infrared radiation, and smaller amounts of ultraviolet and other forms of electromagnetic radiation.

Uses Of Solar Energy

The potential for solar energy is enormous, since about 200,000 times the world’s total daily electric-generating capacity is received by Earth every day in the form of solar energy. Unfortunately, though solar energy itself is free, the high cost of its collection, conversion, and storage still limits its exploitation in many places. Solar radiation can be converted either into thermal energy (heat) or into electrical energy, though the former is easier to accomplish.

Thermal energy

Among the most common devices used to capture solar energy and convert it to thermal energy are flat-plate collectors, which are used for solar heatingapplications. Because the intensity of solar radiation at Earth’s surface is so low, these collectors must be large in area. Even in sunny parts of the world’s temperate regions, for instance, a collector must have a surface area of about 40 square metres (430 square feet) to gather enough energy to serve the energy needs of one person.

The most widely used flat-plate collectors consist of a blackened metal plate, covered with one or two sheets of glass, that is heated by the sunlight falling on it. This heat is then transferred to air or water, called carrier fluids, that flow past the back of the plate. The heat may be used directly, or it may be transferred to another medium for storage. Flat-plate collectors are commonly used for solar water heaters and house heating. The storage of heat for use at night or on cloudy days is commonly accomplished by using insulated tanks to store the water heated during sunny periods. Such a system can supply a home with hot water drawn from the storage tank, or, with the warmed water flowing through tubes in floors and ceilings, it can provide space heating. Flat-plate collectors typically heat carrier fluids to temperatures ranging from 66 to 93 °C (150 to 200 °F). The efficiency of such collectors (i.e., the proportion of the energy received that they convert into usable energy) ranges from 20 to 80 percent, depending on the design of the collector.

Another method of thermal energy conversion is found in solar ponds, which are bodies of salt water designed to collect and store solar energy. The heat extracted from such ponds enables the production of chemicals, food, textiles, and other industrial products and can also be used to warm greenhouses, swimming pools, and livestock buildings. Solar ponds are sometimes used to produce electricity through the use of the organic Rankine cycle engine, a relatively efficient and economical means of solar energy conversion, which is especially useful in remote locations. Solar ponds are fairly expensive to install and maintain and are generally limited to warm rural areas.

On a smaller scale, the Sun’s energy can also be harnessed to cook food in specially designed solar ovens. Solar ovens typically concentrate sunlight from over a wide area to a central point, where a black-surfaced vessel converts the sunlight into heat. The ovens are typically portable and require no other fuel inputs.

Electricity generation

Solar radiation may be converted directly into electricity by solar cells(photovoltaic cells). In such cells, a small electric voltage is generated when light strikes the junction between a metal and a semiconductor (such as silicon) or the junction between two different semiconductors. The power generated by a single photovoltaic cell is typically only about two watts. By connecting large numbers of individual cells together, however, as in solar-panel arrays, hundreds or even thousands of kilowatts of electric power can be generated in a solar electric plant or in a large household array. The energy efficiency of most present-day photovoltaic cells is only about 15 to 20 percent, and, since the intensity of solar radiation is low to begin with, large and costly assemblies of such cells are required to produce even moderate amounts of power.

Small photovoltaic cells that operate on sunlight or artificial light have found major use in low-power applications—as power sources for calculators and watches, for example. Larger units have been used to provide power for water pumps and communications systems in remote areas and for weather and communications satellites. Classic crystalline silicon panels and emerging technologies using thin-film solar cells, including building-integrated photovoltaics, can be installed by homeowners and businesses on their rooftops to replace or augment the conventional electric supply.

Concentrated solar power plants employ concentrating, or focusing, collectors to concentrate sunlight received from a wide area onto a small blackened receiver, thereby considerably increasing the light’s intensity in order to produce high temperatures. The arrays of carefully aligned mirrors or lenses can focus enough sunlight to heat a target to temperatures of 2,000 °C (3,600 °F) or more. This heat can then be used to operate a boiler, which in turn generates steam for a steam turbine electric generator power plant. For producing steam directly, the movable mirrors can be arranged so as to concentrate large amounts of solar radiation upon blackened pipes through which water is circulated and thereby heated.

Other applications

Solar energy is also used on a small scale for purposes other than those described above. In some countries, for instance, solar energy is used to produce salt from seawater by evaporation. Similarly, solar-powered desalination units transform salt water into drinking water by converting the Sun’s energy to heat, directly or indirectly, to drive the desalination process.

Solar technology has also emerged for the clean and renewable production of hydrogen as an alternative energy source. Mimicking the process of photosynthesis, artificial leaves are silicon-based devices that use solar energy to split water into hydrogen and oxygen, leaving virtually no pollutants. Further work is needed to improve the efficiency and cost-effectiveness of these devices for industrial use.


It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi. 

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

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