How to Calculate Redshift

Redshift is a term used in astronomy to describe the displacement of light waves toward the red end of the spectrum. Waves that shift in this manner are considered to be lengthening, which is one of the evidences used to judge that the distance between two objects is increasing. American astronomer Edwin Hubble first reported in 1929 that distant galaxies were receding from Earth's position in the Milky Way galaxy, and that their redshifts were increasing proportionally with their increasing distance. This gave rise to Hubble's law, which is used to measure the recessional velocity of objects from each other in space.

Things You'll Need

• calculator
• paper
• pencil

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Instructions

1. • 1

     Record the rest wavelength of light traveling between two objects. This is defined as the wavelength of the spectral line when there is no relative motion between the two objects.

   • 2

     Record the observed wavelength of light traveling between two objects when they are in relative motion to each other.

   • 3

     Subtract the rest wavelength from the observed wavelength, then divide that quantity by the rest wavelength. The resulting value is usually labeled with the letter z, and is known as the redshift. A positive value for z denotes that the wavelength is lengthening and that the two objects are moving further apart.