Speed from Light Wavelength Shift

The Speed from Light Wavelength Shift calculator computes the relative speed of an object based on the shift in wavelength of the observed emitted light verses the normal (not shifted) wavelength of light emitted.

INSTRUCTIONS: Choose units and enter the following:

• (Δλ) Shift in Wavelength of Light Emitted
• (λ) Normal Wavelength of Light Emitted

Relative Speed (v):  The calculator returns the relative velocity in meters per second and multiples of the speed of light (c).  However, these can be automatically converted to other velocity units via the pull-down menu.  

The Math / Science

For objects moving a speeds well below the speed of light there is a simple relationship between the speed of the object, the shift in the wavelength of the light emitted by the object, and the unshifted wavelength of the light (what the wavelength would be if the object were not moving). This equation computes that speed based on the other two numbers.

The formula for velocity based on light wavelength shift is:

v = (Δλ / λ) * c

where:

• v = velocity 
• Δλ = shift in wavelength of light
• λ = base wavelength of light
• c = speed of light

Astronomy Calculators