All of these discoveries have been further supported throughout the 20th century. Some more observations of the cosmic microwave background radiation were found by the COBE, WMAP, and Planck satellites. Some more observations of the redshift were found by the 2dfGRS and SDSS. These are known as redshift surveys. Survey is this context refers to an astronomical survey. An astronomical survey is a place in space. A redshift survey is a survey that looks for redshifts.