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Hubble's Law Equation:
Where:
d = distance (Mpc)
v = recessional velocity (km/s)
H₀ = Hubble constant (km/s/Mpc)
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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 velocity, H₀ is the Hubble constant, and d is distance.
The calculator uses Hubble's Law in the form:
Where:
Explanation: The equation shows that the distance to a galaxy is proportional to its recessional velocity divided by the Hubble constant.
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 large-scale structure of the universe.
Tips: Enter the galaxy's recessional velocity in km/s and the Hubble constant value (default is 70 km/s/Mpc). The calculator will compute the distance in megaparsecs (Mpc).
Q1: What is the current best value for H₀?
A: Current estimates range from 67-74 km/s/Mpc. The Planck mission measured 67.4, while local measurements give about 73.
Q2: Why are there different values for H₀?
A: Different measurement methods (CMB vs. local distance ladder) give slightly different results, known as the "Hubble tension."
Q3: How accurate is distance from Hubble's Law?
A: It works well for distant galaxies but has uncertainties from peculiar velocities for nearby galaxies.
Q4: What is a megaparsec?
A: 1 Mpc = 3.26 million light-years = 3.086 × 10¹⁹ km.
Q5: Can this be used for very distant galaxies?
A: For z > 0.1, relativistic corrections become important and the simple Hubble's Law becomes less accurate.