Astronomy › Section T · Galaxies and quasars › Topic T.5
The expanding universe
Nearly every galaxy is moving away from us, and the farther it is, the faster it recedes. That simple pattern, Hubble's law, means the universe is expanding, and it turns a galaxy's spectrum into a measure of its distance.
In this topic
- Slipher's surprising spectra
- From theory to law
- Hubble's law and the Hubble constant
- Redshift and recession speed
- Worked example: distance from a spectrum
- Worked example: no centre needed
- Space itself stretches
- What does not expand
- A changing rate and the Hubble tension
- Common mistakes to avoid
- Key takeaways
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