ATRONOMY – RADIO ATRONOMY & IGNAL (30) CALCULATOR
Redshift Recession Velocity
A precise tool.
What is the Redshift Recession Velocity & How does it work?
Redshift (z) measures how much the wavelength of light from a distant astronomical source has been stretched by the expansion of the Universe. A larger z indicates a greater distance and a higher apparent recession speed. In radio astronomy, measuring z from spectral lines allows us to infer how fast a galaxy or quasar is moving away from us. For modest redshifts (z << 1) the relationship between redshift and recession velocity is approximately linear (v ≈ z·c). However, at higher redshifts relativistic effects become important, and the full special‑relativistic Doppler formula must be used to convert z into a physical velocity. The relativistic conversion is given by the formula below, which accounts for time dilation and the Lorentz transformation. By inserting the measured redshift and the speed of light, we obtain the recession velocity in km·s⁻¹, a key parameter for cosmological distance calculations.
v = c frac{(1+z)^2 – 1}{(1+z)^2 + 1}
v = recession velocity, c = speed of light, z = redshift
Parameters
Result
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Frequently Asked Questions
How do I calculate the recession velocity from redshift?
Use Hubble’s Law: v = H₀ * z, where v is the recession velocity, H₀ is the Hubble constant (about 70 km/s/Mpc), and z is the redshift.
What does a higher redshift indicate?
A higher redshift indicates that the galaxy or quasar is moving away from us faster and is located at a greater distance in the universe.
Can this calculator be used for any type of celestial object?
Yes, it can be used for any distant astronomical object emitting light that shows redshift due to the expansion of the universe.
What is the relationship between redshift and distance?
For small redshifts, there is a linear relationship between redshift and distance based on Hubble’s Law.
How accurate is this calculator for very high redshifts?
The accuracy decreases for very high redshifts due to the non-linear effects of cosmology beyond the Hubble flow.
Results are for informational purposes only and do not constitute professional advice.