In physical cosmology and astronomy, dark energy is an unknown form of energy which is hypothesized to permeate all of space, tending to accelerate the expansion of the universe. In other words dark energy is the term used for a possible unseen influence that might be causing the universal expansion to accelerate.
The Dark Energy Survey (D.E.S.) is an optical and near-infrared survey that aims to probe the dynamics of the expansion of the Universe and the growth of large-scale structure.
The D.E.S. collaboration plans to complete a 5000-square-degree survey in the southern sky spread out over 5 years. The survey is planned to reach a depth of 24th magnitude in i band¹ over the entire area. The survey area was chosen to overlap with the survey area of the South Pole Telescope² because its technique of finding clusters through the SZ effect complements the optical techniques employed by D.E.S.. The survey area also overlaps with the survey areas for S.D.S.S. and the Vista Hemisphere Survey because these surveys can provide more information about the galaxies imaged by D.E.S.. Within the 5000-square-degree area there are five smaller patches totaling 30 square degrees which will use longer exposure times and faster observing cadence to search for supernovae.
First light was achieved on 12 September 2012; after a verification and testing period, scientific survey observations started in August 2013. D.E.S. observes about 105 nights per season, lasting from August to February. D.E.S. has now completed image taking for two seasons, Year 1 (August 2013-February 2014) and Year 2 (August 2014-February 2015).
1: The NATO I band is the obsolete designation given to the radio frequencies from 8 000 to 10 000 MHz (equivalent to wavelengths between 3.75 and 3 cm) during the cold war period.
2: The South Pole Telescope (S.P.T.) is a 10 meter (394 in) diameter telescope located at the Amundsen–Scott South Pole Station, Antarctica. The telescope is designed for observations in the microwave, millimeter-wave, and submillimeter-wave regions of the electromagnetic spectrum, with the particular design goal of measuring the faint, diffuse emission from the cosmic microwave background (C.M.B.). The first major survey with the S.P.T.–designed to find distant, massive, clusters of galaxies through their interaction with the C.M.B., with the goal of constraining the dark energy equation of state–was completed in October 2011. In early 2012, a new camera was installed on the S.P.T. with even greater sensitivity and the capability to measure the polarization of incoming light. This camera is designed to measure the so-called “B-mode” or “curl” component of the polarized C.M.B., leading to constraints on the mass of the neutrino and the energy scale of inflation.