The sun spreads its rays of light in the form of electromagnetic radiation. These have different names and forms such as ultraviolet rays, gamma rays, infrared rays, radiowaves, microwaves, visible rays, etc.
The most dangerous among all the rays mentioned above are the ultraviolet (UV) rays. These rays are invisible except that when they fall on certain kinds of material they can make them emit visible light by emitting electromagnetic radiation of lower energy.
The earth has a high intensity oxygenated ozone layer as its cover which absorbs most of the ultraviolet rays. But if the ozone layer becomes thin as, indeed, it has, some of the UV rays reach the earth and may be a hazard to human life and health.
Image Source : cdc.gov
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UV rays can cause sunburn, alteration of connective tissue of dermis, tanning of skin and even skin cancer and other diseases.
Ordinarily, we can get only limited protection against UV rays even by sitting in shade as under a tree.
Curiously, however, the UV rays cannot penetrate glass. Thus we can protect our eyes against UV rays by wearing sun-glass of various kinds. If eyes are not protected against UV rays, we can contract even cataract. If we consult a doctor or a scientific expert, he may tell us about several hazards which may be caused by UV radiations.
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We can take certain steps to protect ourselves against the fury of UV radiations, such as keeping infants in shade, limiting midday sun, wearing hat, sunglasses, protective clothing, applying sunscreen, etc.
It is rightly said that we should not look at the sun at the time of solar eclipse as that way; we can get our eyes harmed by the UV rays emitted by the sun.