Here's how it works:
1. Light Waves: Like sound waves, light waves have a frequency, which determines their color.
2. Moving Source: When a light source is moving towards us, the waves get compressed, resulting in a higher frequency (shifted towards the blue end of the spectrum). This is called blueshift.
3. Receding Source: When a light source is moving away from us, the waves get stretched out, resulting in a lower frequency (shifted towards the red end of the spectrum). This is called redshift.
How Astronomers Measure It:
* Spectroscopy: Astronomers use specialized instruments called spectrographs to split the light from stars into its individual wavelengths, creating a spectrum.
* Spectral Lines: Each element in a star's atmosphere absorbs light at specific wavelengths, creating dark lines called absorption lines in the spectrum.
* Shift in Lines: If the star is moving, these absorption lines will be shifted to slightly different wavelengths compared to the same lines in a stationary source.
* Measuring Shift: By carefully measuring the shift in these lines, astronomers can calculate the radial velocity of the star, which is its speed towards or away from us.
Important Note: Doppler shift only measures the velocity component along our line of sight. It doesn't tell us anything about the star's motion perpendicular to our view.
