Definition
Electromagnetic radiation with wavelengths shorter than visible light but longer than X-rays, roughly 10 to 400 nanometers. The sun is the primary natural source, and ultraviolet radiation increases with altitude as the atmosphere thins and filters less of it.
Plain English
A type of invisible light from the sun. You can't see it, but it's strong enough to burn skin and damage eyes, and there's more of it the higher you fly.
Context Anchor
Pilots encounter this term in weather, high-altitude flight, health, and cockpit sun-exposure discussions.
Derivation
From Latin 'ultra' meaning 'beyond' and 'violet,' the color at the short-wavelength end of the visible spectrum. So 'ultraviolet' literally means 'beyond violet' -- the invisible light just past the violet end of what the eye can see.
Why Pilots Care
At altitude, exposure rises sharply and increases risks of skin damage and material degradation on exposed aircraft parts.
Grounding Statement
If you are flying in strong sunlight and your skin or eyes are exposed, ultraviolet radiation may be affecting you even though you cannot see it.
Intuition Check
Do not read “radiation” here as radioactive material. Ultraviolet radiation is invisible light energy, mainly from the sun, not contamination or fallout.
Example Sentence 1
At cruise altitude, ultraviolet radiation exposure is much higher than on the ground, so the pilot wore sunglasses rated to block it.
Example Sentence 2
Ultraviolet radiation gradually faded the paint on the wing surfaces over years of outdoor storage.