Why do stars exhibit red or blue shifts?

Stars exhibit red or blue shifts due to the Doppler Effect, which is a change in frequency or wavelength caused by relative motion.

The Doppler Effect is a fundamental concept in physics, named after the Austrian physicist Christian Doppler who proposed it in the 19th century. It refers to the change in frequency or wavelength of a wave in relation to an observer who is moving relative to the wave source. In the context of astronomy, this effect is observed when stars or galaxies are moving away from or towards us.

When a star is moving away from us, the light waves from the star are stretched out, causing them to appear more red. This is known as a red shift. Conversely, when a star is moving towards us, the light waves are compressed, making them appear more blue. This is referred to as a blue shift. The degree of shift can give us information about the speed at which the star or galaxy is moving.

The Doppler Effect is not only limited to light but also applies to sound. For instance, the change in pitch of a passing siren is a common example of the Doppler Effect. As the siren approaches, the sound waves are compressed leading to a higher pitch, and as it moves away, the sound waves are stretched resulting in a lower pitch.

In the field of astrophysics, the red or blue shift of stars and galaxies is a crucial tool for understanding the universe. It provides evidence for the expansion of the universe, a key aspect of the Big Bang Theory. By measuring the redshift, astronomers can determine the speed at which galaxies are moving away from us, and hence estimate the age and size of the universe. Furthermore, the Doppler Effect is also used in the search for exoplanets. By observing the small red or blue shifts in the light from a star, scientists can infer the presence of a planet causing the star to wobble slightly.