Science Puzzle
Why Are Astronauts’ Visors Coated in Gold?
When astronauts work outside a spacecraft in sunshine, they pull a shiny visor down over their helmets. The visor isn't just gold-coloured: it's coated with real gold, so thin that they can see straight through it.
Why use gold?
The Answer
A very thin layer of gold reflects most of the Sun's heat, its infrared light, while still letting through enough ordinary light to see by. It protects the astronaut's eyes and face from the fierce, unfiltered sunshine of space.
Sunlight is more than the colours we see. It also carries infrared, which we feel as heat, and ultraviolet, which causes sunburn. On Earth, the atmosphere softens some of this. In space there's nothing in the way, and the Sun is dazzling, hot and harsh. The visor itself blocks harmful ultraviolet, and the gold coating handles the heat.
Gold is excellent at reflecting infrared. A layer only about 50 billionths of a metre thick, less than a thousandth of the width of a hair, bounces most of it away, yet lets through enough visible light to see clearly, tinted gold. Gold also never tarnishes, so it keeps working, and it can be spread incredibly thin. Gold visors have been used since the Gemini missions of the 1960s.
The same property explains why the James Webb Space Telescope's huge mirror is coated with gold: it's designed to collect infrared light, and gold reflects infrared better than almost anything else.
The principle: Selective reflection. A very thin layer of gold reflects most infrared while letting enough visible light through, so it shields the eyes from the Sun's heat without blinding the wearer.