Hubble's law and the distance ladder
H0 is fitted as sum(v d) / sum(d^2) to galaxies far enough that peculiar velocities are small; every distance rests on a ladder of parallax, Cepheids and supernovae, whose calibration sets H0, now 73 from the ladder and 67.4 from the cosmic background.
About 30 minutes8 activities Paper packet
What helps before this
- Active galactic nuclei Go over it