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How Astronomers Know — Evidence Lab

Galaxy Redshift and an Expanding Universe

Estimated time
~30 min
Saved locally on this device
Learning goals
  • Farther galaxies recede faster, and the slope of that relation gives the Hubble constant H0 — a direct measurement of the rate of cosmic expansion.
  • HS-ESS1-2 — Students weigh multiple independent evidence lines for the Big Bang.
Help & glossary
  • Use the hint ladder before checking your answer — hints get more specific.
  • Incorrect answers can be retried. Feedback explains why.
  • Constructed responses (CER) are self-checked — nothing is sent to a server.

Question 1 of 3

Read the illustrative Hubble diagram below. Estimate the Hubble constant H0 as the ratio of recession velocity (km/s) to distance (Mpc).

The Hubble constant H0 is the slope of a plot of galaxy recession velocity against distance. Modern estimates lie roughly between 67 and 74 (km/s)/Mpc.

(km/s)/Mpc

    Sources