Imagine light is made of tiny, super-fast cars. Each color (red, orange, yellow...) is a different model. Astronomers have this fancy tool called a spectroscope that acts like a space traffic cam, snapping pics of these light-cars as they zoom by.
Now, here’s the weird part:
Stars Going Too Fast???—???When a star whooshes TOWARDS us, the light-cars get squished together, making them look more blue. Scientists call that a "blueshift." Think of it like a Doppler radar for stars.
Stars Taking It Slow???—???When a star’s cruising AWAY, those light-cars get stretched out, looking more red. That’s a "redshift," and it tells astronomers how far away that star is.