Each point on the above diagram shows the line-of-sight recession velocity versus distance for a number of distant galaxies. Describe how the recession velocities of galaxies are measured by astronomers. Explain the different techniques used by astronomers to measure the distances to galaxies, and describe how these methods are used to construct the distance ladder.

Each point on the above diagram shows the line-of-sight recession velocity versus distance for a number of distant galaxies. Describe how the recession velocities of galaxies are measured by astronomers. Explain the different techniques used by astronomers to measure the distances to galaxies, and describe how these methods are used to construct the distance ladder.