A fire truck drives past Maren with its siren on. What happens to the pitch she hears as it passes her?
Astronomers photograph the spectrum of a distant star. The familiar pattern of lines is all there, but every line sits at a longer wavelength than the same pattern measured in a lab. Something moved the whole pattern.
You have met this with sound. When a source of sound moves away from you, the frequency you receive is lower than the frequency it emits: the Doppler effect. Light does exactly the same, in color.
Light from a source moving away from the observer is received at a longer wavelength and a lower frequency.
On the visible band, longer wavelengths lie toward the red end. So this change is called redshift.
Light from a source moving toward the observer is received at a shorter wavelength and a higher frequency.
Shorter wavelengths lie toward the blue end. This change is called blueshift.
The spectrum of a star moving away from Earth is shifted toward the red.
So the opening star's displaced line pattern has one reading: the star is moving away.
The shift works in every electromagnetic band, not just visible light; the names redshift and blueshift stay even for radio waves.
A star's spectral lines are received at shorter wavelengths than the lab pattern. What is the star doing?
Shorter received wavelengths mean blueshift.
Blueshift comes from a source moving toward the observer.
The star is moving toward Earth.
A space probe flying away from Earth transmits radio signals at one fixed frequency. How does the received frequency on Earth compare?
The probe is a source moving away.
A receding source's waves are received at lower frequency.
The received frequency is lower than the transmitted one.
A light source moves away from an observer. How is its light received?
A light source moves toward an observer. What happens to the received wavelength?
Wanda says: 'Light from a star moving away from Earth is received at a longer wavelength than it was emitted.' Is Wanda correct?
Every line in a star's spectrum sits at a longer wavelength than the lab-measured pattern. Which statement is correct?
A light source approaches an observer at a steady speed. Which statement describes the received light?
Starlight is received at longer wavelengths than it was emitted. Which term names this change?