Final answer:
Evidence for dark matter includes galaxy rotation curves and gravitational lensing, both of which suggest the presence of unseen mass influencing the motion and light around galaxies and galaxy clusters.
Step-by-step explanation:
The clear evidence for dark matter comes from several astronomical observations:
- Galaxy rotation curves: The flat rotation curves of spiral galaxies, which do not decrease with distance from the galactic center as expected if only luminous matter were present, imply the existence of a massive galactic halo of dark matter.
- Gravitational lensing: The bending of light from distant objects due to massive galaxy clusters, which can only be explained by the presence of additional mass that is not visible, indicating the presence of dark matter.
While supernovas and Cepheid variable stars are important for measuring distances in the universe, they do not provide direct evidence for dark matter.