The Sun is a Star

The Sun is the star at the center of the Solar System. The Sun has a diameter of about 1,392,000 kilometers (865,000 mi) (about 109 Earths), and by itself accounts for about 99.86% of the Solar System’s mass; the remainder consists of the planets (including Earth), asteroids, meteoroids, comets, and dust in orbit. About three-quarters of the Sun’s mass consists of hydrogen, while most of the rest is helium. Less than 2% consists of other elements, including iron, oxygen, carbon, neon, and others.

The Sun’s color is white, although from the surface of the Earth it may appear yellow because of atmospheric scattering. Its stellar classification, based on spectral class, is G2V, and is informally designated a yellow star, because the majority of its radiation is in the yellow-green portion of the visible spectrum. In this spectral class label, G2 indicates its surface temperature of approximately 5,780 K (5,510 °C.), and V (Roman five) indicates that the Sun, like most stars, is a main sequence star, and thus generates its energy by nuclear fusion of hydrogen nuclei into helium. Astronomers once regarded the Sun as a small and relatively insignificant star, it is now presumed to be brighter than 85% of the stars in the Milky Way galaxy, most of which are red dwarfs. Estimates for its magnitude are 4.8. The Sun’s hot corona continuously expands in space creating the solar wind, a hypersonic stream of charged particles that extends to the heliopause at roughly 100 AU. The bubble in the interstellar medium formed by the solar wind, the heliosphere, is the largest continuous structure in the Solar System.

The Sun is currently traveling through the Local Interstellar Cloud in the Local Bubble zone, within the inner rim of the Orion Arm of the Milky Way galaxy. Of the 50 nearest stellar systems within 17 light-years from Earth, the Sun ranks 4th in mass. The Sun orbits the center of the Milky Way at a distance of approximately 24,000–26,000 light years from the galactic center, completing one clockwise orbit, as viewed from the galactic north pole, in about 225–250 million years.

The mean distance of the Sun from the Earth is approximately 149.6 million kilometers (1 AU), though this varies as the Earth moves from perihelion in January to aphelion in July. At this average distance, light travels from the Sun to Earth in about 8 minutes and 19 seconds. The energy of this sunlight supports almost all life on Earth via photosynthesis, and drives Earth’s climate and weather. The enormous impact of the Sun on the Earth has been recognized since pre-historic times, and the Sun has been regarded by some cultures as a deity. An accurate scientific understanding of the Sun developed slowly, and as recently as the 19th century prominent scientists had little knowledge of the Sun’s physical composition and source of energy. This understanding is still developing; there are a number of present-day anomalies in the Sun’s behavior that remain unexplained.

Sun Light Observation and Effects

Sunlight is very bright, and looking directly at the Sun with the naked eye for brief periods can be painful, but is not particularly hazardous for normal, non-dilated eyes. Looking directly at the Sun causes phosphene visual artifacts and temporary partial blindness. It also delivers about 4 milliwatts of sunlight to the retina, slightly heating it and potentially causing damage in eyes that cannot respond properly to the brightness. UV exposure gradually yellows the lens of the eye over a period of years and is thought to contribute to the formation of cataracts, but this depends on general exposure to solar UV, not on whether one looks directly at the Sun. 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; conditions are worsened by young eyes or new lens implants (which admit more UV than aging natural eyes), Sun angles near the zenith, and observing locations at high altitude.

Viewing the Sun through light-concentrating optics such as binoculars is very hazardous without an appropriate filter that blocks UV and substantially dims the sunlight. An attenuating (ND) filter might not filter UV and so is still dangerous. Attenuating filters to view the Sun should be specifically designed for that use: some improvised filters pass UV or IR rays that can harm the eye at high brightness levels. Unfiltered binoculars can deliver over 500 times as much energy to the retina as using the naked eye, killing retinal cells almost instantly (even though the power per unit area of image on the retina is the same, the heat cannot dissipate fast enough because the image is larger). Even brief glances at the midday Sun through unfiltered binoculars can cause permanent blindness.

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. This can damage or kill those cells, resulting in small permanent blind spots for the viewer. 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, and the 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.

A rare optical phenomenon may occur shortly after sunset or before sunrise, known as a green flash. The flash is caused by light from the Sun just below the horizon being bent (usually through a temperature inversion) towards the observer. Light of shorter wavelengths (violet, blue, green) is bent more than that of longer wavelengths (yellow, orange, red) but the violet and blue light is scattered more, leaving light that is perceived as green.

Ultraviolet light from the Sun has antiseptic properties and can be used to sanitize tools and water. It also causes sunburn, and has other medical effects such as the production of vitamin D. Ultraviolet light is strongly attenuated by Earth’s ozone layer, so that the amount of UV varies greatly with latitude and has been partially responsible for many biological adaptations, including variations in human skin color in different regions of the globe.

Play It Safe – Wear Sun Hats

The head must be protected from the heat and rays of the sun. If you happen to visit a beach or are out in the open country with a blazing sun, it’s advisable for you to wear a sun hat. A sun hat is not a fashion item, but required health protection. The sun’s rays can cause sun stroke and blisters on your scalp. If a person happens to be bald, their head can sweat profusely in the heat. Appropriate headgear is worn as part of the uniform by the defense forces of the world. This is to protect them from the rays of the sun. Sun rays can also cause skin diseases and skin cancer. Therefore, it is imperative to wear appropriate hats. If you are going to spend time outdoors in the sun, the hat you wear should have a wide brim so that the back of the neck, the forehead, and the ears, and sides of the face are protected from the sun’s rays.

When buying a hat, choose one that is made of a natural fiber such as cotton. There should also be small vents on the side of the hats. Natural fiber is cooler than synthetic fiber, and the vents will allow the flow of air on the scalp. When buying a sun hat, buy one that is of thick material and is white or some light color. White and light colored sun hats do not absorb the sun’s heat. So, they serve as additional protection for the head.

People who live in hot or tropical climates wear some form of headgear to protect their heads from the rays and heat of the sun. They wear it to safeguard their health. There are definite health benefits to wearing sun hats. One major health benefit is that your scalp will not get burnt, and also your chances of suffering from a sun stroke are reduced, and of course, your skin is protected from skin cancer, which may be caused by the ultra violet rays of the sun.

How long or thick your hair may be, it’s still advisable to wear a sun hat whenever you are out in the sun. Even if you are pottering around in the garden, or getting a sun tan, you must wear a sun hat. If you happen to have delicate skin, then it becomes all the more necessary to wear a hat.

So, wearing a proper hat that will protect your head and parts of your face is essential. The sun’s rays can cause serious skin damage. The skin takes a long time to heal from sunburn. So, why take a risk when wearing a hat will protect your head and is also beneficial for your health. In case you are going to a country where the temperatures are high and there is plenty of sunshine, remember to buy and take a sun hat. The biggest organ of the body is the skin and nobody wants to damage their skin.

Overexposure to the Sun Can Happen Indoors and Outdoors

Journal of the American Academy of Dermatology article offers information about the recent development in sun protection provided by window and automobile glass, and sunglasses.

In the car, at work or walking to and from a store, you can’t escape the sun’s ultraviolet (UV) rays. However, new research about the transmission of UV light through window and automobile glass and through sunglasses, has led to developments that can help protect people from the sun.

“People should realize that even during everyday activities they are receiving incidental sun exposure which harms the skin as it accumulates and can result in premature aging, wrinkles and even skin cancer,” said dermatologist Henry W. Lim, M.D., chairman of the department of dermatology, Henry Ford Hospital in Detroit, Mich., and co-author of the Journal of the American Academy of Dermatology article entitled, “Photoprotection by window glass, automobile glass and sunglasses.” “Dermatologists and manufacturers of glass products and sunglasses are continually working to find better ways to decrease the amount of UV radiation being filtered through these items to the skin and eyes. These advances are helping to reduce the amount of UV exposure that a person receives on a daily basis.”

UV radiation from the sun comes in two forms: ultraviolet A (UVA) and ultraviolet B (UVB). UVB has long been associated with sunburn while UVA has been recognized as a deeper penetrating radiation that contributes to premature aging and wrinkle formation. Both of these types of rays have been linked to the development of skin cancer. More than 1 million new cases of skin cancer are diagnosed each year.

Window Glass and Photoprotection

Window glass filters out UVB rays, but UVA rays are still transmitted to the skin through the panes. The type of glass and the type of coating on the glass can affect the percentage of UV radiation that is transmitted to the body.

Most residential buildings have one of three types of glass: clear, tinted or reflective. Of these three, reflective glass, the kind that eliminates the ability to see the interior of a building from the outside during the day, minimizes unwanted solar heat gain and reduces UV transmission to less than 25 percent. This means nearly one-quarter of the UV exposure, exclusively the longer wavelength UVA, is reaching the inside though, remarked Dr. Lim.

“Most Americans spend 80 percent of their day indoors at work or school,” stated Dr. Lim. “With the new trend in architecture toward more and larger windows in buildings, protection from UV exposure when indoors has become an important issue for not only the cost-effectiveness of cooling a building, but also for the health and safety of the employees who work within it.”

Recent developments in window glass include low-emissivity (low-E) glass which has a special surface coating between layers of antireflective glass. This type of glass reflects up to 70 percent of solar heat and reduces UV transmission through the panes to 20 percent.

To protect the skin from the damaging rays of the sun when working indoors, it is important to: arrange workspace so that the body is not in direct sunlight; and use blinds or shades on the windows during peak sun hours.

Automobile Glass and Photoprotection

In studies of UV exposure in cars, it was shown that the parts of the driver’s and passenger’s bodies closest to the window received the greatest UV exposure. Side and rear windows are usually made from non-laminated glass, allowing a significant amount of UVA to pass through to the passengers in the car. Most windshields are made from laminated glass, the type of glass designed to prevent fragments from shattering onto the occupants during an accident and which can filter both UVB and a large portion of the UVA rays.

Tinting automobile glass is an option that allows 3.8 times less UVA light to be transmitted to the interior of the car as compared to untinted window glass. In a 2004 study of UV transmission and color tint, grey tinted laminated glass provided the highest UV protection with only 0.9 percent of UVA light transmitted versus 62.8 percent transmitted through non-laminated clear glass. People who are considering tinting their windows should take their car to a professional auto detailing shop, in order to ensure that the tinting meets the federally mandated 70 percent of minimum visible light transmittance through the windshield.

“Obviously UVA exposure in a car is influenced by non-glass-related factors such as position of the individual in the vehicle, direction of travel with respect to the sun, and time of day,” stated Dr. Lim. “However, the more time a person spends in a car, especially at the same time of day such as during a regular commute, can greatly affect the amount of UV exposure their skin receives.”

To reduce sun exposure while driving, wear protective clothing, such as a long-sleeved shirt and pants, especially when the body is in the sun; apply sunscreen generously to any exposed skin before driving, especially the hands, forearms and face; and wear protective sunglasses to reduce glare and protect the eyes from UV exposure.

Sunglasses and Photoprotection UV radiation is potentially hazardous to the structure of the eyes, particularly the cornea, lens and retina, which is why the U.S. developed a “sunglass standard,” with the latest version published in 2001. Sunglasses are classified into three categories: cosmetic sunglasses providing minimal UV protection; general purpose sunglasses designed to reduce glare in bright light or when driving; and special purpose sunglasses for activities such as skiing or going to the beach.

“The ideal sunglasses should substantially reduce UV exposure of the cornea and the lens, including any UV coming from lateral directions, and should wrap around the eyes, thereby maximizing eye and eyelid protection,” said Dr. Lim. “For even better protection, wear a broad-brimmed hat which can help reduce the level of UV radiation reaching the eyes and the surrounding area.”

In addition, Dr. Lim recommended the following tips when purchasing sunglasses to maximize UV protection:

Look for neutral gray and amber brown lenses that give true color rendition, particularly to red and green stoplights. Seek glasses with a large frame and lenses that cover the entire eye and wrap around the side of the eye.

Look for the “100% UV Protection” sticker to ensure that the sunglasses meet standards for safe levels of UV protection.

Expensive sunglasses do not necessarily provide better UV protection, according to Dr. Lim. Darkly tinted sunglasses can make pupils dilate and increase lid opening, thereby resulting in increased UV exposure to the lens of the eye.

In addition to wearing sun protective clothing, including sunglasses, you should follow these sun protection tips and Be Sun SmartSM:

Generously apply sunscreen to all exposed skin using a Sun Protection Factor (SPF) of at least 15 that provides broad-spectrum protection from both ultraviolet A (UVA) and ultraviolet B (UVB) rays. Re-apply every two hours, even on cloudy days, and after swimming or sweating.

Seek shade when appropriate, remembering that the sun’s rays are strongest between 10 a.m. and 4 p.m.

Use extra caution near water, snow and sand as they reflect the damaging rays of the sun which can increase your chance of sunburn.

Protect children from sun exposure by applying sunscreen. Get vitamin D safely through a healthy diet that includes vitamin supplements. Don’t seek the sun.

Avoid tanning beds. Ultraviolet radiation from the sun and tanning beds causes skin cancer and wrinkling. If you want to look like you’ve been in the sun, consider using a sunless self-tanning product, but continue to use sunscreen with it.

Check your birthday suit on your birthday. If you notice anything changing, growing, or bleeding on your skin, see a dermatologist. Skin cancer is very treatable when caught early.

Nature’s Healer: The Sun

The sun has always been seen as the source of life and healing. We must not forget the many benefits the sun bestows on us. It is nature’s healer.

Sunlight

Throughout history there has been no better and more common symbol of happiness and well being than the sun. The ancient Egyptians, the Aztecs, Romans and Greeks all worshipped the sun and thought of it as the source of life and health. Regardless of the historical time that comes to mind, you will find people cheered and uplifted by the life-giving rays of the sun.

Whether it was in the form of the god Helios or establishing Sun-day as the first day of the week, the sun always has played an important role in people’s lives.

The great Greek physician Hippocrates wrote extensively about the sun’s healing powers. Herodotus, the father of Heliotherapy, made frequent statements about the healing properties of the sun in his medical practice. In our own time, we see a reflection of these ancient sentiments in songs, poems and movies. And who of us could deny the feeling we have when the sun breaks through the darkened clouds: our mood lifts; our eyes turn upward; our energy and zest for life returns.

Although there have been many serious medical warnings about overexposure to the sun in recent years, we must not neglect the positive role sunlight plays in our mental and physical health. There is good news coming from scientific research telling us why we look and feel better from the sun.

The Blues

Sunlight is an important part of our daily lives. Ever notice how much time is spent at the office worrying about who gets the office with the window. And what about all that energy you feel when spring and summer come around. Everyone seems to be outdoors, planning hikes, barbecues and pool parties. You name it and it’s happening.

Tom Wehr, M.D., a research psychiatrist at the National Institutes of Health, is an expert in mood disorders and feels that our elevation in mood during the spring and summer can be directly linked to the amount of sunlight we are exposed to. “Researchers have found the exposure to natural light increases the production of serotonin, a chemical that stimulates the brain’s pleasure center, thereby perking up your mood while warding off anxiety and depression.”

In contrast, look at what happens to people in the long winter months, especially those living in the Northeast and Northwest. Over 11 million people suffer from what is called Seasonal Affective Disorder or SAD, and another 25 million suffer from a milder form of “winter blues.”

The symptoms of SAD and the “winter blues” can include fatigue, craving carbohydrates, irritability, sleeping more and a change of personality from your summer self to your winter self. It’s not exactly known what causes SAD, but according to health writer Francis FitzGerald, “SAD occurs year after year during a specific season – usually the winter – and vanishes when spring ushers in longer days and more sunshine.”

Medical Researchers think that our depressed moods during the winter may be the result of a chemical imbalance between serotonin and melatonin. With too little sunlight, melatonin makes us drowsy, and disrupts our internal clock.

Our Bodies

Besides just making us feel better and more energetic, exposure to sunlight plays an important role in helping us create vitamin D in our bodies. What makes this so important? Vitamin D has been shown to help prevent and treat serious medical conditions, including: breast cancer, osteoporosis, prostate cancer, psoriasis, acne, etc.

Though many people aren’t aware of it, most of our physiological requirements for vitamin D are provided for by casual exposure to sunlight. It is easy to see how important sunlight is for our physical and mental health.

Breast Cancer

Over 180,000 women will be diagnosed with breast cancer this year. It is a major concern for women of all ages. But there is hope. According to Judy Gaillard and Donald Smith of Sun Wellness magazine, a study by researcher Ester M. John at the Northern California Cancer Center, entitled “Vitamin D and Breast Cancer Risk…” casual exposure to sunlight, along with other factors, can help reduce the risk of breast cancer.

The scientists concluded “high exposure to sunlight was associated with a 25 percent to 65 percent reduction in breast cancer risk among women whose longest residence was in a state of high solar radiation.” A 25 percent reduction in the number of breast cancer cases would mean approximately 44,000 women would not have to suffer the trauma of this disease. Since vitamin D and sunlight exposure are life-style behaviors, this is good news for women wishing to reduce their risk of breast cancer.

Osteoporosis

Sometimes called “the silent disease,” osteoporosis is the loss of bone mass due to the malabsorption of calcium into the bone. Bone fragility results in increased risk of bone fracture in many parts of the body, including the hips, spinal vertebrae, and ribs. According to James F. Balch, M.D., author of Prescription for Nutritional Healing, fully “half of all women between the ages 45 and 75 show signs of osteoporosis.” Although osteoporosis is mostly an issue for post-menopausal women, both sexes and all age groups suffer from this disease.

“If vitamin D is absent, calcium, which is vital for normal bone growth and development, will not be absorbed from the intestinal tract and the bones become deformed,” says Zane Kime, M.D., M.S. in his book Sunlight. One of the best ways to get adequate vitamin D is moderate exposure to the sun. The World Health Organization Task-Force for Osteoporosis recently recommended sunlight as a part of the treatment and management of this disease.

Prostate Cancer

Prostate cancer is the second most common cause of death from cancer in men over age 75. In a recent study by Hanchette and Schwartz of the University of North Carolina and published in the journal Cancer, the researchers a 20 to 40 percent lower incidence of prostate cancer among men in southern climates. Because of findings like this some researcher are suggesting that vitamin D may be an effective preventive agent against prostate cancer. The importance of sunlight cannot be underestimated in maintaining prostate health. If the incidence of prostate cancer is reduced by 20 percent nearly 37,000 men would not suffer the anguish of this disease.

Athletic Achievement

Most of us believe that sunlight gives us extra pep and energy. During the summer months, we tend to sleep less, play more and just have more get up and go. To back up this idea scientifically, Bylle Dopps and Scott Hoover of Sun Wellness magazine looked at research from the Sports Medicine Department of the German National Olympic Team Training Center. The results of their research showed that routine exposure to the sun optimized performance capabilities and reduced the incidence and recovery time of athletes from minor injuries.

If simple sunlight can help world class athletes recover from the stresses of training and competition, it seems reasonable to conclude that we can all benefit from the stress busting affects of sunlight.

Conclusion

Recent scientific studies have demonstrated what humans have suspected all along: natural sunlight promotes feelings of well-being, improves immune function, promotes natural healing and optimizes athletic performance. Don’t neglect these positive benefits of sunlight. Include moderate exposure to the sun in your overall health regimen.