In order to look back in time, astronomers peer deep into a narrow 'pencil beam' of space. These narrow surveys can be easily confounded by variations in the density of matter on scales larger than the pencil beam.

Benjamin Moster, then at the Max Planck Institute for Astronomy in Heidelberg, Germany, and his colleagues have developed a recipe for measuring uncertainty in density. The team combined measurements of galaxies with models of dark matter, a mysterious material thought to bind galaxies together, and was able to predict how the density variation affects galaxy measurements at different distances from Earth. The results should ensure more accurate interpretation of past and future pencil-beam surveys.

Astrophys. J. 731 113 (2011)