Transcript: Most of the techniques for measuring distance in astronomy depend on well understood properties of stars or entire galaxies. However, if astronomers believe they’ve measured the current expansion rate of the universe then redshift itself can be used to indicate distance. Redshift is defined as the fractional wavelength shift caused by the expansion of the universe on the light of a galaxy. At low redshift it’s also equal to the recession velocity divided by the velocity of light. When this is combined with the Hubble relation you get the expression distance equals redshift times the velocity of light divided by the Hubble constant, so in knowing the Hubble constant and the redshift the distance can be calculated. Redshift maps directly to distance in a linear way at low redshift. For example, if the redshift of a galaxy is one percent, z = 0.01, then the distance is calculated to be just over forty megaparsecs or about a hundred and forty million lightyears.