Ultraviolet Radiation:
The Sun and UV Rays


WHAT IS ultraviolet radiation?
Sun

Well, it helps to start with talking about sunlight...

Sunlight is really just the whole spectrum of the different kinds of energy (electromagnetic radiation) given off by the Sun, energy that we can or cannot see.

MOST OF THESE RAYS ARE:

  • Visible light - so we can see
  • Infrared rays - to provide heat (The energy in the rays make molecules in whatever substance it hits to start vibrating back and forth. It produces heat like when you briskly rub your hands together.)
  • Ultraviolet rays – are invisible to humans (Has high-energy that makes the molecules shake, moved, or split ,not just vibrate which changes chemical structure, causes cell damage, and mutates genetic codes.)


    Ultraviolet (UV) rays have much shorter wavelengths than the visible light but longer wavelengths than x-rays. So, these high-energy UV waves are invisible to the human eye. However, some insects, like bumblebees, can see them, probably to help guide them to certain plants.


    UV Image Sun
    Image Courtesy of NASA.
    False-color image of the Sun
    by SOHO satellite April 2000 taken at an
    extreme UV wavelength.

    The sun is the major source of UV rays; however, special lights like black lights and electric arcs (as in welding) also emit it. This ultraviolet radiation can have both damaging and beneficial effects on living things.

    These ultraviolet rays are called.....

    ‘ultra’(going beyond the limits) + ‘violet’(a color)

    .....because their frequencies are higher than or beyond those that humans see as the color violet. Violet is the color of light at the short-wavelength end of the visible light spectrum for humans at approximately 380-450 nm.

    WHAT's 'nm'? ---A ‘nm’ is an abbreviation for nanometer, which is one billionth, or 10e-9, meters. VERY TINY!!!!
    Ruler


    All these types of energies that move at the speed of light are collectively called ‘electromagnetic radiation.’ The various types of light differ in their wavelengths, frequencies, and energy. The higher energy waves have higher frequencies and shorter wavelengths.

    EyePigments inside the retina of our eyes absorb wavelenghts of light between 400nm-700nm (called "visible light"). We absorb it and so ‘see’ it. (According to an article Ultraviolet Radiation by Brien Sparling at NAS.NASA.gov, Education Resources)


    Energy Spectrum



    Below is a simple breakdown of types of sun radiation including the invisible and visible part of the spectrum based on their wavelengths.

    Scientists have also divided the 3 different wavelength bands of UV rays into: UV-A, UV-B, and UV-C based on how much energy each contains and how they affect living things.

    Infrared(700 nm and above): Invisible. Produces heat/warmth from the sun.
    Light(400 nm to 700 nm): The visible range we can see with the naked eye.
    Ultraviolet A, or UVA (315 nm to 400 nm): Has higher frequency than violet-colored light and thus invisible to human eye. UV-A is least energetic and least harmful of the 3 (UV-A, UV-B, and UV-C). These rays don't have enough energy to affect the ozone so the radiatino passes through the earth atmosphere pretty much unfiltered. Penetrates skin the deepest and damages connective tissue of the skin. A = Aging
    Ultraviolet B, or UVB (280 nm to 315 nm): Has higher frequency than violet-colored light and thus invisible to human eye. Because have lower energy level and longer wavelength than UV-C, some is absorbed by atmosphere and some make it to the earth's surface. UVB rays seem most responsible for the causing sunburns and the skin damage that causes cancer. B = Burning
    Ultraviolet C, or UVC (100 nm to 280 nm): Has higher frequency and shortest wavelength than violet-colored light and thus invisible to humans. Most energetic and harmful potent rays. Due to the ozone layer around the earth, these do not penetrate our atmosphere but the energy is absorbed before reaches earth. (CAUTION: Arc welding emits man-made UV-C rays/light that can cause 'arc eye' which can inflame the cornea and burn the retina so wear protective eye gear!)

    UV Spectrum

    Although most of the Sun's very short wavelength ultraviolet radiation, or UV rays, are filtered out by the Earth's ozone layer, some make it to earth.

    Sun Earth Reflection
    (Image courtesy of NASA, by Robert Simmon.)

    Shown in this image are the different effects different clouds have on the amount of solar energy that reaches earth:
    -- On LEFT is large (cumulus) cloud thunderstorm tower and most of the Sun's energy is reflected.
    -- The MIDDLE middle cloud (cirrus) reflects some short-wave energy but let some through to the surface.
    -- At the RIGHT, in the clear dry regions most of the solar energy reaches the surface.


    It’s the UV rays (ultraviolet radiation) that damage our skin and cause sunburn.
    -- Some penetrate through clouds and windows
    -- Some make it to the earth's surface
    -- Some are very strong at the equator
    -- Some are strong at high elevations
    -- Some are strongest in the summer
    -- Some get absorbed by the ozone layer surrounding the earth

    The AMOUNT of ultraviolet radiation exposure depends on your altitude. It's a matter of how thin the atmosphere is and the smaller number of molecules to scatter and absorb the ultraviolet radiation (not how close you are to the sun). Apparently, for every 1000 feet you go up in altitude, the UV levels may increase about 4%. Helpful as a rule of them if you are watching this sort of thing closely to monitor skin and sunburn protection.

    FOR YOUR INFORMATION



    WavelengthA Wavelength is the distance between repeating units of a wave of a given frequency. Like waves seen in light, water waves, sound waves.




    FrequenciesA frequency is the number of occurrences of a repeating event per unit of time.






    Go to "Skin Anatomy" | See "Skin Cancer" | Go to "Sunburn"

    See "Freckles & Melanin" | See "Vitamin D" | See "Heatstroke"

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