Caption: This image of the galaxy cluster ZwCl0024+1652 is created using mathematical modelling, together with observations from the Hubble Space Telescope (HST). The Hubble observations were taken in November 2004 by the Advanced Camera for Surveys (ACS). The exquisite resolution of the ACS, allowed very detailed measurements to be made of the gravitational lensing in the cluster. The blue nebulosity is a superimposed ""map"" of the dark matter distribution in the galaxy cluster and is not visible in the observations, but is a mathematical model created based on the gravitational lensing data. The ""dark matter ring"" the is present in the image is one of the strongest pieces of evidence to date for the existence of dark matter. Observational data provides evidence that Dark matter makes up about 1/4 of the Universe, and is believed to make up the underlying structure of the cosmos. In addition, a large percentage the mass in galaxies and galaxy clusters is dark matter, which is not visible via direct observations.
Credit: NASA, ESA, M.J. Jee and H. Ford (Johns Hopkins University) credit link

Caption: This image shows a map of the distribution of galaxies and is based on redshift data from the Sloan Digital Sky Survey (SDSS). Redshift measurements provides information on the distances, positions and motions of the galaxies. The Earth is located at the center of the image, and each dot represents a galaxy. The outer circle represents a ""distance"" of about 2 billion light years. The idea of distance in cosmology is complex because the usual measurement of distance is the separation between two points in space at the same time. However, because of the speed of light, the further a distance, the farther back in time we are observing. The numbers on the outer circle are Right Ascension coordinates mapped onto a flat circle, and provides information on the position of the galaxies on the sky. The colours used represent the ages of the stars in the galaxies, the redder, more strongly clustered points represent galaxies comprising of older stars. The dark wedges that do not contain any dots are regions that were not mapped by the SDSS due to dust from the Milky Way galaxy obscuring the view.
Credit: M. Blanton and Sloan Digital Sky Survey credit link