1. What is the Hubble Constant?

The Hubble Constant (H₀) is a measure of the rate of expansion of the universe, relating the recession velocities of galaxies to their distances. It is a fundamental parameter in cosmology with units of kilometers per second per megaparsec (km/s/Mpc).

2. How Does the Calculator Work?

The calculator uses Hubble's Law equation:

Where:

• \( H_0 \) — Hubble Constant (km/s/Mpc)
• \( v \) — Recession velocity of galaxy (km/s)
• \( d \) — Distance to galaxy (Mpc)

Explanation: The equation shows the linear relationship between a galaxy's distance and its recession velocity due to the expansion of the universe.

3. Importance of Hubble's Law

Details: The Hubble Constant is crucial for determining the age and size of the universe, understanding cosmic expansion, and studying dark energy. It helps astronomers measure distances to faraway galaxies.

4. Using the Calculator

Tips: Enter recession velocity in km/s and distance in megaparsecs (Mpc). Both values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: What is the current accepted value of H₀?
A: There's tension between values: ~67 km/s/Mpc (Planck) and ~73 km/s/Mpc (local measurements). This "Hubble tension" is an active research area.

Q2: Why are the units km/s/Mpc?
A: These units show that for each megaparsec of distance, the recession velocity increases by H₀ kilometers per second.

Q3: How was the Hubble Constant first measured?
A: Edwin Hubble first estimated it in 1929 using Cepheid variable stars as distance markers and redshift measurements.

Q4: What affects the accuracy of H₀ measurements?
A: Key challenges include precise distance measurements, peculiar velocities of galaxies, and cosmic variance.

Q5: How does H₀ relate to the age of the universe?
A: The Hubble time (1/H₀) gives a rough estimate of the universe's age, though this needs adjustment for changing expansion rates.