How is the Doppler Effect used to detect invisible planets?

Answer 1

As a planet revolves around a star, it actually wiggles the star a bit (the bigger the planet, the more it wiggles the star). This causes the star to be moving towards as a bit, then away from us a bit (and repeat forever).

As a star moves away from us, the Doppler effect (also known as a redshift) makes the star appear a little redder and as a star moves towards us, it appears a little bluer.

If we see a star, getting a little bluer, then a little redder, then a little bluer again and so on, you know that the star is wiggling, and that would only be caused if the star has something in its orbit, like a planet.

So even though we can't see the planet, we know it is there.

Answer 2

The Doppler Effect is used to detect invisible planets through the observation of the slight wobble in a star's movement caused by the gravitational pull of an orbiting planet. As the planet orbits the star, it causes the star to move slightly towards and away from Earth, resulting in a shift in the star's spectral lines that can be observed using telescopes and spectrographs. By measuring these shifts, scientists can infer the presence and characteristics of the unseen planet.