Redshift Velocity
Calculator
Results
- Recession velocity (km/s)
- 14,989.6229
- Relativistic velocity (km/s)
- 14,615.327916
- Velocity as a fraction of c
- 0.048751
Astronomy results
| Recession velocity (km/s) | 14,989.6229 |
| Relativistic velocity (km/s) | 14,615.327916 |
| Velocity as a fraction of c | 0.048751 |
formula-map diagram
- Recession velocity (km/s)
- 14,989.6229
- Relativistic velocity (km/s)
- 14,615.327916
- Velocity as a fraction of c
- 0.048751
Astronomical relationship
Formula
v = c z (low z); v = c[(1+z)² − 1] / [(1+z)² + 1]= 14989.6229
Note
This result is a simplified model: it applies the displayed textbook formula to the values you entered, assuming ideal spherical bodies, circular orbits, blackbody radiation and perfect optics, and ignoring atmospheric seeing, relativistic corrections beyond those stated, cosmological models and measurement uncertainty. Use published ephemerides and catalogue data for real observations.
More in Astronomy and space
See all →Frequently asked questions
What does redshift tell us about a galaxy's motion?+
Redshift measures how much a galaxy's light has been stretched to longer (redder) wavelengths, which for nearby galaxies indicates how fast it's receding from us via the Doppler effect. A larger redshift value corresponds to a higher recession velocity.
How is recession velocity calculated from redshift?+
For non-relativistic speeds, velocity approximately equals redshift (z) multiplied by the speed of light: v ≈ zc. This simple formula works well for z well below 1; at higher redshifts, the full relativistic Doppler formula is needed instead.
Why is almost every distant galaxy redshifted rather than blueshifted?+
Because the universe is expanding, space itself is stretching between us and distant galaxies, carrying their light to longer wavelengths as it travels. Only a few nearby galaxies, like Andromeda, are blueshifted because their local gravitational pull toward us outweighs the cosmic expansion.
Is redshift caused by galaxies physically moving through space, like a car speeding away?+
Not exactly — for cosmological redshift, it's the expansion of space itself stretching the light's wavelength during its long journey, rather than the galaxy moving through static space like a receding car. The simple v = zc formula treats it like Doppler motion as a useful approximation, but the underlying physics is really about spacetime expansion.
Does a redshift value of z = 1 mean the galaxy is moving at the speed of light?+
No, that's a common misreading of the simple formula, which breaks down at high z. A redshift of z = 1 corresponds to roughly 70-75% the speed of light using the correct relativistic treatment, not exactly the speed of light as the naive v = zc formula would suggest.