Reading light from space — Astronomy, 14–17 years
Starlight carries clues about a distant object’s temperature, composition and motion. A spectrum spreads that light into colours and wavelengths that astronomers can measure.
Light has a pattern
White light is a mixture of many wavelengths. A prism or a spectroscope spreads them out. Dark or bright lines appear when atoms absorb or emit particular wavelengths, like fingerprints made of light.
The problem of unreachable stars
Astronomers cannot usually collect a piece of a star or visit it with a laboratory instrument. They needed a way to identify matter at a distance. Laboratory spectra became a reference key for interpreting starlight.
Finding hydrogen
Suppose a star’s spectrum has a line at 656 nanometres. Laboratory hydrogen has a well-known line at about 656 nanometres. Matching the lines gives strong evidence that hydrogen is present in the star’s outer gas.
A colour is not an element
It is reasonable to think that a red star must contain a red substance. Colour mainly tells us about the light’s wavelengths and often its temperature; specific narrow lines, not the overall colour, reveal elements.
Space chemistry
Spectroscopy is used to study stars, planets and distant galaxies. It can reveal gases in a planet’s atmosphere, helping researchers test whether a world has water vapour or other important molecules.
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