The Sloan Digital Sky Survey or SDSS is a major multi-spectral imaging and spectroscopic redshift survey using a dedicated 2.5-m wide-angle optical telescope at Apache Point Observatory in New Mexico, United States. The project was named after the Alfred P. Sloan Foundation, which contributed significant funding.
A consortium of the University of Washington and Princeton University was established to conduct a redshift survey, to look at a section of the sky to measure the redshift of astronomical objects: usually galaxies, but sometimes other objects such as galaxy clusters or quasars. Using Hubble’s law, the redshift can be used to estimate the distance of an object from Earth. The redshift is defined as a shift toward longer wavelengths of the spectral lines emitted by a celestial object that is caused by the object moving away from the earth.
The Sloan Digital Sky Survey has created the most detailed three-dimensional maps of the Universe ever made, with deep multi-color images of one-third of the sky, and spectra for more than three million astronomical objects.
Photometric observations were taken with the SDSS imaging camera and cover 14,555 square degrees on the sky (just over 35% of the full sky back in 2011. The next year the data includes the first results from the Baryon Oscillation Spectroscopic Survey (BOSS), including over 800,000 new spectra. Over 500,000 of the new spectra are of objects in the Universe 7 billion years ago (roughly half the age of the universe).
In 2013, data was released with the first results from the APO Galactic Evolution Experiment (APOGEE), including over 57,000 high-resolution infrared spectra of stars in the Milky Way. DR10 also includes over 670,000 new BOSS spectra of galaxies and quasars in the distant universe.
In July 2020, after a 20-year-long survey, astrophysicists of the Sloan Digital Sky Survey published the largest, most detailed 3D map of the universe so far, filled a gap of 11 billion years in its expansion history, and provided data that supports the theory of a flat geometry of the universe and confirms that different regions seem to be expanding at different speeds
The SDSS (98 in) telescope is used for the Sloan Digital Sky Survey and began operating in 2000. It is a Ritchey-Chrétien reflector on an alt-azimuth mount housed under a roll-off enclosure. It was designed with an unusually large 3° field of view to better support its primary task of surveying the entire sky.
- Apache Point Observatory is an astronomical observatory located in the Sacramento Mountains in Sunspot, New Mexico, United States, approximately 18 miles south of Cloudcroft. The observatory is operated by New Mexico State University and by the Astrophysical Research Consortium.
- Alfred P. Sloan was an American business executive in the automotive industry. He was a long-time president, chairman, and CEO of General Motors Corporation.
- BOSS was designed to measure the expansion rate of the Universe. It mapped the spatial distribution of luminous red galaxies (LRGs) and quasars to determine their spatial distribution and detect the characteristic scale imprinted by baryon acoustic oscillations in the early universe.
- APOGEE-1 employed high-resolution, high signal-to-noise infrared spectroscopy to penetrate the dust that obscures significant fractions of the disk and bulge of our Galaxy. APOGEE-1 aimed to survey 100,000 red giant stars across the full range of the Galactic bulge, bar, disk, and halo. At its conclusion, APOGEE-1 observed over 150,000 stars.
- Ritchey-Chrétien telescope was invented in the early 1910s by American astronomer George Willis Ritchey and French astronomer Henri Chrétien. Ritchey constructed the first successful RCT, which had an aperture diameter of 24 inches in 1927 (e.g. Ritchey 24-inch reflector). The second RCT was a 40 in instrument constructed by Ritchey for the United States Naval Observatory; that telescope is still in operation at the Naval Observatory Flagstaff Station.