Doppler Effect and Red Shift
Have you ever noticed how the sound of a siren changes as an ambulance passes by? It sounds higher pitched as it gets closer and lower as it moves away. This is called the Doppler Effect! It happens because the sound waves get squished together when the ambulance moves towards you and stretched out when it moves away.
Stars, like our Sun, emit light. But not just any light! This light contains a unique 'fingerprint' called spectral lines. These lines are like a barcode that tells us what elements the star is made of. When we look at light from a star through a special tool, we can see these lines. Each element, like hydrogen or helium, has its own special pattern of lines.
Just like the ambulance siren, light waves also experience the Doppler Effect! When a star or galaxy moves away from us, its light waves get stretched out. This makes the light appear redder than it actually is, a phenomenon called 'redshift'. If it moves towards us, the light waves get squished, making it appear bluer, called 'blueshift'. Redshift tells us that objects are moving away.