https://astro.unl.edu/classaction/animations/coordsmotion/transitmovie.html

This website helps to show the frequency changes in waves with moving objects.

Go to: https://svs.gsfc.nasa.gov/20241 to see a visualization of the spectrum.

Go to:
https://imagine.gsfc.nasa.gov/science/toolbox/emspectrum1.html
to learn about the spectrum.