Why Brightly Colored Spheres Are Strung Across Power Lines
Simple Things – Surprising Histories explains why brightly colored spheres are strung along power lines. Known as aerial marker balls, they make otherwise difficult-to-see wires more visible to pilots. These brightly colored spheres, known as aerial marker balls, easily mark the presence of power lines that can otherwise appear invisible from the air.
Officially, they are called aerial marker balls. Their sole purpose is to act as bright, high-visibility stop signs in the sky. They scream to pilots, “Warning! There is a wire here.” You will almost always find them in areas where aircraft fly low near airports, deep valleys, or major highway crossings.
FAA guidance specifies their size, color, spacing, and placement.
Mandated by the Federal Aviation Administration, they’re often up to 36 in across. That’s 3 feet in diameter. And they can weigh up to 17 lbs each. They’re painted in highly specific, high-contrast colors like aviation orange, white, or yellow, ensuring they stand out perfectly against nature’s blues and greens. And installing them is nothing short of thrilling. Because power lines are often suspended over rugged terrain or wide rivers, these marker balls are routinely installed by highly trained linemen riding on the outside of hovering helicopters.
