What is Ultraviolet Radiation?

What is ultraviolet radiation?  Here’s a hint… It's an invisible part of sunshine.
 
Think back to your high school science classes and remember how the teacher used a prism to break up a beam of light into a rainbow of colors.  Then recall the teacher explaining that all these visible colors are only one part of the full Electromagnetic Spectrum.  Out beyond the red end of the rainbow there are infrared (IR), microwaves and radio waves.  On the other side of the visible colors, out beyond the deep purple, there are ultraviolet (UV) and x-rays.  Even though you can't see these wavelengths with your eyes, you know they exist, because of the magical things they do like sending data to our cellphones, heating our food in a microwave or showing a broken bone inside our body.
 
The largest energy source in our solar system is the Sun.  Even though it's 93 million miles away, it provides the energy we need for life here on Earth.  The sunshine that we see with our eyes is only a small part of the energy from the sun – it also sends out energy across much of the Electromagnetic Spectrum.  Luckily, the Earth's atmosphere protects us from potentially harmful things such as x-rays and most (but not all) of the ultraviolet (UV) energy.  Therefore, we need to remember that any time we are in the visible sunshine, we're also getting hit with some invisible ultraviolet radiation.  
 
Diving in deeper, we find that ultraviolet radiation is divided into three parts: ultraviolet A (UVA), ultraviolet B (UVB) and ultraviolet C (UVC).  The UVC portion is completely blocked by the earth's ozone layer and atmosphere.  Also, much of the UVB is absorbed by the ozone layer, but some of the UVB does reach the Earth’s surface.  However, the bigger concern is ultraviolet A (UVA).  The UVA radiation is not blocked at all by the atmosphere, so it reaches us here on the Earth's surface.  This UVA radiation can reach deeper into our skin, so we need to be careful to avoid overexposure to the sun.
 
Most of us are familiar with the rules of sunshine safety.  We know that most dangerous time of day for sun exposure is the later morning hours through mid-afternoon.  We're aware that if we are outdoors for more than a brief time during these hours, we need to apply sunscreen with sun protection factor (SPF) 15 or higher, that gives both UVA and UVB protection.  We recall that wearing a hat with a wide brim, and clothes with long sleeves will shield us from the sun.  We know that repeated overexposure to UV radiation can lead to serious health issues, including skin cancer.  
 
Fun fact – sunshine and ultraviolet exposure aren't all bad.  A few minutes of sunshine a couple of times a week helps your body produce vitamin D; a vitamin essential to human health.


Source: CDC, CPC, EPA, NASA
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Image: Diagram of Electromagnetic Radiation (NASA, 2016).