Learning objectives
Describe redshift as the shift of known spectral lines from distant galaxies towards longer wavelengths, measured by comparing observed and laboratory wavelengths.
Calculate the recession speed of a galaxy from its redshift using Δλ/λ ≈ Δf/f ≈ v/c.
Explain how the redshifts of galaxies in every direction point to an expanding Universe.
Apply Hubble's law v ≈ H₀d with H₀ in s⁻¹, and explain why recession speeds that grow with distance suggest the Universe began in a hot, dense Big Bang.
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