The Doppler effect refers to the change in frequency or wavelength of a wave (such as sound, light, or electromagnetic waves) as observed by someone who is moving relative to the source of the waves.
When the source of the waves is moving toward an observer, the waves are compressed, resulting in a higher frequency (or shorter wavelength). This is called a blue shift in the case of light waves. Conversely, when the source is moving away from the observer, the waves are stretched, resulting in a lower frequency (or longer wavelength). This is called a red shift for light waves.
In astronomy, the Doppler effect is especially important for understanding the movement of celestial objects. By analyzing the red shift or blue shift of light from stars, galaxies, and other cosmic objects, astronomers can determine whether these objects are moving toward or away from Earth. Here’s how it connects:
- Red Shift: When galaxies or stars are moving away from us, the light they emit is stretched, causing it to shift toward the red end of the spectrum. This is a key piece of evidence for the expansion of the universe—galaxies appear to be moving away from us, and the farther they are, the faster they seem to be receding.
- Blue Shift: If an object is moving toward Earth, its light will shift toward the blue end of the spectrum. This is observed in some galaxies, like the Andromeda Galaxy, which is on a collision course with the Milky Way.
By studying the Doppler shifts of light from stars and galaxies, astronomers can measure the speed and direction of their motion, helping to map the dynamics of our universe.
In addition to galaxies, Doppler shifts also help with detecting exoplanets. When an exoplanet orbits a star, it can cause the star to move slightly in response. This small movement causes a Doppler shift in the star’s light, which can be measured and used to infer the presence of the exoplanet.