1. What is Hubble's Law?

Hubble's Law describes the relationship between the distance to a galaxy and its recessional velocity due to the expansion of the universe. It is expressed as v = H₀ × d, where v is the velocity, H₀ is the Hubble constant, and d is the distance.

2. How Does the Calculator Work?

The calculator uses Hubble's Law equation:

Where:

• \( v \) — Recessional velocity (km/s)
• \( H_0 \) — Hubble constant (km/s/Mpc)
• \( d \) — Distance to galaxy (Mpc)

Explanation: The equation shows the linear relationship between a galaxy's distance and its velocity moving away from us.

3. Importance of Hubble's Law

Details: Hubble's Law provides evidence for the expanding universe and is fundamental to modern cosmology. It allows astronomers to estimate distances to faraway galaxies and study the expansion rate of the universe.

4. Using the Calculator

Tips: Enter the Hubble constant (typically around 70 km/s/Mpc) and the distance to the galaxy in megaparsecs (Mpc). All values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: What is the current best estimate for H₀?
A: The Planck mission estimates H₀ ≈ 67.4 km/s/Mpc, while local measurements give ≈73 km/s/Mpc. This discrepancy is known as the "Hubble tension."

Q2: Why are the units km/s/Mpc?
A: These units indicate that for every megaparsec of distance, the velocity increases by the H₀ value in km/s due to cosmic expansion.

Q3: Does Hubble's Law work for all distances?
A: It works well for distances beyond our Local Group (d > 10 Mpc). At smaller scales, gravitational interactions dominate over cosmic expansion.

Q4: How is distance measured for Hubble's Law?
A: Astronomers use standard candles like Cepheid variables or Type Ia supernovae to measure distances to galaxies.

Q5: What does Hubble's Law tell us about the universe?
A: It provides evidence for the Big Bang theory and allows us to estimate the age of the universe (≈1/H₀).