Red-Shift😆
Our Sun contains helium. We know this because there are black lines in the spectrum of the light from the Sun where helium has absorbed light. These lines form the absorption spectrum for helium. You will have to know this well for I/GCSE Physics.
Spectrum of the sun☀️
When we look at the spectrum of a distant star, we still see an absorption spectrum. However, the pattern of lines has moved towards the red end of the spectrum.
Spectrum of a distant star✨
The positions of the lines have changed because of the Doppler effect. Their wavelengths have increased (and their frequencies have decreased).
Astronomers have found that the further from us a star is, the more its light is red-shifted. This tells us that distant galaxies are moving away from us, and that the further away a galaxy is, the faster it's moving away.
Since we cannot assume that we have a special place in the Universe, this is evidence for a generally expanding universe. It suggests that everything is moving away from everything else.
References: https://www.igcsephysics.com/content/edexcel/topics/cosmology/page257/page257_img1.jpg
Drafted by Catrina (Physics)