ultraviolet radiation

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Electromagnetic radiation of wavelengths from about 400 to 10 nanometres (where the X-ray range begins). Physiologically, ultraviolet radiation is extremely powerful, producing sunburn and causing the formation of vitamin D in the skin. Ultraviolet radiation is invisible to the human eye, but its effects can be demonstrated.

Levels of ultraviolet radiation have risen an average of 6.8% a decade in the northern hemisphere and 9.9% in the southern hemisphere 1972–96, according to data gathered by the Total Ozone Mapping Spectrometer on the Nimbus 7 satellite. Ultraviolet rays are strongly germicidal and may be produced artificially by mercury vapour and arc lamps for therapeutic use. The radiation may be detected with ordinary photographic plates or films. It can also be studied by its fluorescent effect on certain materials. The desert iguana Disposaurus dorsalis uses it to locate the boundaries of its territory and to find food.

The stars are said to represent Syria and Iraq. Red, white, black, and green are the pan-Arab colours. Effective date: 29 March 1980. >>