How can I teach infrared light using asteroid detection?
Asteroids glow in infrared because they are warmed by the Sun, so infrared telescopes can find dark asteroids and measure their sizes better than visible-light telescopes.
The electromagnetic spectrum is a key physics topic, and asteroid detection provides a good application of infrared radiation.
Reflection versus emission. In visible light, we see asteroids because they reflect sunlight. Dark asteroids reflect very little, so they appear faint and may be missed, or their sizes underestimated. In infrared, asteroids are seen by the heat they emit. Sunlight warms them, and they radiate infrared. A dark asteroid absorbs more sunlight and so is warmer, glowing brightly in infrared.
Measuring size. Combining visible and infrared observations allows scientists to work out both the size and the reflectivity, or albedo, of an asteroid. A small bright asteroid and a large dark one can look equally bright in visible light, but they differ in infrared.
Space telescopes. Infrared telescopes work best in space, above Earth's atmosphere, which absorbs much infrared and itself glows. NASA's NEOWISE mission surveyed asteroids in infrared from 2013 to 2024. The planned NEO Surveyor telescope is designed to find most near-Earth asteroids larger than 140 metres. The James Webb Space Telescope, which observes in infrared, measured the size of asteroid 2024 YR4 in 2025.
Classroom demonstration. If you have a thermal imaging camera, show how objects at different temperatures appear. A dark and a light object left in sunlight or under a lamp warm up differently, demonstrating why dark asteroids glow more in infrared.
Link. Discuss how different wavelengths reveal different information, from radio meteor detection to X-ray analysis of meteorites.
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