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Calculate Redshift and Blueshift

Calculator for the blue- or redshift and the resulting radial velocity.


As the Doppler effect for sound, there is also a Doppler effect for light. If a light source moves towards the observer, the distance between the arriving waves gets shorter, the color of light shifts to blue. If a light source moves from the observer away, the distance between the arriving waves gets longer, the color of light shifts to red. This change of color is only perceptible at very high velocity, so redshift and blueshift are most commonly found in astronomy. From the magnitude of color change, the radial velocity can be calculated, which is the velocity away from the observer. Radial velocity is an important dimension at the measurement of stars and galaxies. As the universe expands and so most galaxies move away from us, redshift is more common than blueshift.


Redshift and Blueshift z

Redshift and blueshift are labeled with z. If z is positive, it is a redshift, negative z stands for blueshift. The formula is z = λ/λ0 - 1. Please enter two values, the third value and the radial velocity will be calculated.

Observed wavelength λ:
Original wavelength λ0:
Shift z:



Radial velocity v

The radial velocity is the velocity towards the observer (negative), or from the observer away (positive). It is calculated from the shift z in percent of the speed of light and in meters per second. The formula is v = c * [(1+z)²-1] / [(1+z)²+1] with the speed of light c as 299792458 meters per second. z has to be larger as -1.

Shift z:
Radial velocity v in %c:
Radial velocity v in m/s:




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