Astronomy & space · Grades 8–12
Light, spectra and astronomical evidence · revision notes
Radio, infrared, visible, ultraviolet, X-rays and gamma rays are electromagnetic radiation. Astronomy uses more than the light visible to human eyes.
Key ideas and conditions
Electromagnetic spectrum
Radio, infrared, visible, ultraviolet, X-rays and gamma rays are electromagnetic radiation. Astronomy uses more than the light visible to human eyes.
Wave relation
In vacuum, frequency and wavelength satisfy c=fλ. Shorter wavelength therefore means higher frequency at fixed propagation speed.
Spectra
Spectral features can constrain composition and physical conditions. A spectrum is evidence interpreted through models, not a labelled photograph of individual atoms.
Lookback
Light takes time to travel. Seeing a distant object means receiving information emitted earlier, with cosmological interpretation requiring care at very large distances.
Explain without looking
- Distinguish an observed spectral line from an inferred chemical identification.
- When we observe light from a distant star, are we seeing information from its present local moment?
Further reading and review references
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