Credit: NASA ozonewatch. Johann Ritter's experiment was designed toexpose photographic paper to light just beyondthe visible spectrum and prove the existenceof light beyond violet—ultraviolet light. Credit: Troy Benesch. Electromagnetic Spectrum Series Series Homepage. Infrared Waves. Reflected Near-Infrared.
Visible Light. Earth's Radiation Budget. Diagram of the Electromagnetic Spectrum. Recommended Articles. September 24, Solar Eclipse - June 10, June 09, Aurora-Chasing Citizen Scientists Help November 13, The extreme ultraviolet, abbreviated EUV, is the ultraviolet light closest to X-rays, and is the most energetic of the three types.
The far ultraviolet, abbreviated FUV, lies between the near and extreme ultraviolet regions. It is the least explored of the three regions. Our Sun emits light at all the different wavelengths in electromagnetic spectrum, but it is ultraviolet waves that are responsible for causing our sunburns.
To the left is an image of the Sun taken at an Extreme Ultraviolet wavelength - Angstroms to be exact. An Angstrom is a unit length equal to 10 meters. Though some ultraviolet waves from the Sun penetrate Earth's atmosphere, most of them are blocked from entering by various gases like Ozone.
Some days, more ultraviolet waves get through our atmosphere. Scientists have developed a UV index to help people protect themselves from these harmful ultraviolet waves. The higher energy, shorter wavelength far UV region spans wavelengths between 91 and nm. Extreme UV radiation has the shortest wavelength range and highest energies of the regions of the ultraviolet spectrum, and lies on the border between UV and X-ray radiation. Extreme UV radiation spans the 10 to 30 nm wavelength range.
Normal air is largely opaque to UV with wavelengths shorter than nm; oxygen absorbs "light" in that part of the UV spectrum. That is good news for us Earthlings, since our atmosphere shields us from the most dangerous, highest energy portions of the UV spectrum that reach our planet from the Sun and other sources in space.
When discussing the impact of UV radiation on the environment and human health, scientists subdivide the ultraviolet spectrum in a different way. It is the closest UV radiation to visible light. This can be useful for chemical processing, or it can be damaging to materials and living tissues. This damage can be beneficial, for instance, in disinfecting surfaces, but it can also be harmful, particularly to skin and eyes, which are most adversely affected by higher-energy UVB and UVC radiation.
Most of the natural UV light people encounter comes from the sun. However, only about 10 percent of sunlight is UV, and only about one-third of this penetrates the atmosphere to reach the ground, according to the National Toxicology Program NTP. No measurable UVC from solar radiation reaches the Earth's surface, because ozone, molecular oxygen and water vapor in the upper atmosphere completely absorb the shortest UV wavelengths. A suntan is a reaction to exposure to harmful UVB rays. Essentially, a suntan results from the body's natural defense mechanism kicking in.
This consists of a pigment called melanin, which is produced by cells in the skin called melanocytes. Melanin absorbs UV light and dissipates it as heat. When the body senses sun damage, it sends melanin into surrounding cells and tries to protect them from sustaining more damage.
The pigment causes the skin to darken. However, continued exposure to UV radiation can overwhelm the body's defenses. When this happens, a toxic reaction occurs, resulting in sunburn.
UV rays can damage the DNA in the body's cells. The body senses this destruction and floods the area with blood to help with the healing process.
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