Dark lightning (noun, “Dark LITE-ning”)
Dark lightning refers to bursts of gamma radiation that can occur during thunderstorms.
Gamma radiation — made up of gamma rays — is a kind of light. Gamma rays pack the most energy of all radiation that occurs naturally on Earth. And dark lightning is a natural source of gamma radiation. That’s why some experts call dark lightning by another name: terrestrial gamma-ray flashes.
We cannot see dark lightning. That’s because we cannot see gamma rays. Our eyes can only detect light within a specific wavelength range. Light within that range is what we call “visible light.” Any light outside that range is invisible to us. Gamma rays have much shorter wavelengths than the light in our visible range.
Scientists think the same processes that create regular, visible lightning also create dark lightning. But some details of that process remain a mystery.
Lightning occurs when opposing electrical charges build up at the top and bottom of a storm cloud. Often, a negative charge builds up at the bottom of a cloud and the top remains more positive. These electrical fields energize electrons. Sometimes, this difference discharges as a bolt of electricity. We see that as regular lightning.
Experts think dark lightning arises in much the same way. Energized particles can crash into atoms in our atmosphere. Collisions between atoms and the high-velocity particles releases a lot of energy. And these collisions can emit gamma rays. Scientists suspect this may contribute to bursts of dark lightning.
However, it must require just the right conditions because dark lightning is rarer than regular lightning. Experts estimate about a thousand bursts of regular lightning occur for every one bolt of dark lightning.
In a sentence
Rare flashes of invisible dark lightning may occasionally expose plane passengers to gamma radiation.
