Physics
Infrared Radiation
Quick fact
Infrared radiation was discovered in 1800 by astronomer William Herschel, who measured a temperature increase just beyond the red part of the visible spectrum.
Why this is interesting
You've felt the warmth of the sun on your skin, but have you ever wondered why you can't see the heat?
Read the full explanation
Understanding Infrared Radiation
Infrared radiation is a band of invisible light that lies between visible red light and microwaves on the electromagnetic spectrum. Every object with a temperature above absolute zero (-273°C) emits infrared energy—the hotter the object, the more it emits. You experience this every time you stand near a campfire: the warmth you feel is infrared radiation traveling directly from the fire to your skin. Unlike conduction, which needs contact, or convection, which relies on air movement, infrared radiation can pass through a vacuum—that's why the Sun's heat reaches Earth through space.
A deeper explanation
The mechanism behind infrared radiation is rooted in the motion of atoms and molecules. As particles vibrate due to thermal energy, they create oscillating electric and magnetic fields that propagate as waves. The specific wavelengths emitted depend on the temperature, described by Planck's law of blackbody radiation. This is why objects glow red when hot enough (their emission shifts into the visible spectrum). Infrared radiation is crucial because it transfers energy without a medium, enabling technologies like thermal imaging cameras (which detect temperature differences), remote controls (using infrared LEDs), and astronomical observations of cool stars and interstellar dust. Its absorption by greenhouse gases (like CO2 and water vapor) also plays a vital role in Earth's climate.