Expanding Universe? How was this determined?

Question

How did the scientists determine that the Universe is expanding? What did the method consist of? Could you please try to explain it to me?

Thanks!

Answer 1

Stars are mostly hydrogen gas, with some helium and heavier elements mixed in.  Star light (and sun light) therefore have spectral lines of hydrogen in the light they emit.  SO if you made a spectograph of sunlight, you could pick out the wavelengths of light due to hydrogen.  Now when a source of light moves relative to you, the wavelength is shifted either to shorter or longer wavelength depending on where teh source of light is moving toward you or away from you.  This is called the doppler shift.  The amount of shift is related to how fst the source is moving.

Now when astronomers measure teh spectra of stars in distant galaxies, they see the hydrogen spectrum shifted to longer wavelengths.  Thus they know that the distance galaxies are all moving away from us and approximately the rate of expansion.  That is how it is determined that the universe is expanding.

Answer 2

by doppler's effect of light or to be more precise red shift

Answer 3

I think they measured light waves received from space and determined that everything was racing away from everything else as the light was taking longer to reach them.