Hubble's law and expansion of the universe
Galaxies and cosmology · Physics
Solar system
Interactive 3DAll eight planets in orbit around the Sun, with Saturn's rings and Earth's Moon.
Controls
Drag the sliders or type a value — the simulation updates live.
Study notes
Step 1: Pick a galaxy distance. Let’s say it is 20 million light‑years away. Step 2: Convert that distance to megaparsecs. 1 megaparsec ≈ 3.26 million light‑years, so 20 million light‑years ÷ 3.26 ≈ 6.14 Mpc. Step 3: Use Hubble’s law v = H₀ × d. Take H₀ ≈ 70 km/s/Mpc. Step 4: Multiply: v = 70 × 6.14 ≈ 430 km/s. Step 5: Interpretation – that galaxy is moving away from us at about 430 kilometers per second. Step 6: Check: If the galaxy were 40 million light‑years away, the distance in Mpc would be 12.28 Mpc and the speed would be 70 × 12.28 ≈ 860 km/s, exactly double the first speed, confirming the linear relationship.