BRAINCAKEThe Doppler Effect and Red Shift
When a source of waves moves relative to an observer, the observed frequency and wavelength change. This is the Doppler effect.
• source moving away: wavelength increases, frequency decreases: red shift
• source moving towards the observer: wavelength decreases: blue shift
Astronomers measure the shift of known absorption lines (for example hydrogen lines) in a star's or galaxy's spectrum. For speeds much less than the speed of light (v << c):
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Key terms in this lesson
- absorption line
- A dark line at a specific wavelength in an otherwise continuous spectrum, produced when atoms or ions absorb photons of that wavelength.
More in Astrophysics
- Evolution of a Star
- Supernovae, Neutron Stars and Black Holes
- The Schwarzschild Radius
- Type Ia Supernovae as Standard Candles
- Hubble's Law
- The Big Bang Theory and the Age of the Universe
- Quasars
- Detecting Exoplanets
All 24 lessons in Astrophysics · All AQA A-level Physics topics