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NASA looks at ultraviolet radiation

UV levels over the United States in August 2000  

ATLANTA, Georgia (CNN) -- Scientists from NASA's Goddard Space Flight Center in Greenbelt, Maryland, pieced together a year's worth of images from the Total Ozone Mapping Spectrometer (TOMS) orbiting aboard the Earth Probe spacecraft for a moving glimpse at global ultraviolet (UV) radiation.

The Earth Probe satellite travels on a polar orbit about 740 kilometers above the surface, crossing the equator every day at noon local time. Using measurements of ozone, cloud cover and solar radiation escaping from the top of the atmosphere, TOMS estimates the amount of radiation reaching the earth.

The animations, released on Goddard's Web site on Wednesday, show traveling hot spots focused around the middle of the globe, particularly during the summer months of the Southern Hemisphere (winter in the Northern Hemisphere), where cloud cover is thin.

"That's because of the ITCZ -- the Intertropical Conversion Zone," says Jay Herman, a NASA project scientist at Goddard. "It has to do with the motions of clouds and the peculiarity of the way land mass is distributed."

"There are more clear-sky days in the Southern Hemisphere than there are in the Northern Hemisphere," he says. "Australia has one of the lowest number of cloudy days than any place on earth, except for South Africa."

Thin air at higher elevations -- like the Himalayas and the Rockies -- also raises the UV levels, but higher latitudes -- closer to the poles -- counteract that effect.

Use protection

But what does all that mean for the typical earthling?

"If you live in the middle latitudes, where most people live, nothing much," Herman said. "Protect yourself from the sun. But people living at higher latitudes are at greater risk than they used to be because of the ozone depletion."

That would include northern Europe, Canada, and the southernmost portions of South America and Africa.

Two types of UV radiation -- UVA, which is blocked by glass, and UVB, which is not -- do the most damage. UVB rays are the primary cause of sunburn and skin cancer, while UVA rays penetrate deeper in the skin's base layer, attributing to both cancer and sunburns.

Both rays can damage the body's immune system.

The American Academy of Dermatology (AAD) says that half of all new cancers are skin cancers -- and that melanoma, a particularly virulent form of skin cancer, kills one person per hour on average. And while it's certainly not the only cause of skin cancer, exposure to the sun is perhaps the most important preventable cause, say dermatologists.

The Food and Drug Administration (FDA) and the AAD recognize six skin categories, ranging from light-pigmented skin that is extremely sensitive to the sun's effects to darker-pigmented skin that almost never burns.

But dermatologists say everyone should take precautions when dealing with the sun, including using a sunscreen that protects against both UVA and UVB rays and staying out of the sun during the hottest part of the day -- generally 10 a.m. to 4 p.m.

• NASA - Goddard Space Flight Center
• The American Academy of Dermatology
• Welcome to the American Cancer Society

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