The SDSS
The Sloan Digital Sky Survey is an international collaboration to create the most complete three-dimensional map of the sky. This survey uses a 2.5 meter telescope located at the Apache Point Observatory in New Mexico. It is one of the most ambitious and influential astronomical surveys ever conducted and has surveyed about a third of the sky, obtaining optical images and spectra of astronomical objects. The SDSS has helped scientists measure properties and distances of these objects and has revolutionized our understanding of the universe by providing high-quality, publicly accessible data since the beginning of the project in 2000.
Phases
The SDSS has gone through many phases from the 2000 to the present: SDSS-I (2000-2005), SDSS-II (2005-2008), SDSS-III (2008-2014), SDSS-IV (2014-2020) and the most recent phase is SDDS-V which started in 2020. The most recent complete phase, SDSS-IV, was comprised of three different surveys: eBOSS, APOGEE-a and MaNGA. MaNGA stands for Mapping Nearby Galaxies at APO and focused on producing spectra measurements across the entire face of many nearby galaxies.
APOGEE stands for Apache Point Observatory Galactic Evolution Survey and it mapped the Milky Way stars in an attempt to better understand how our galaxy formed and evolved. eBOSS stands for Extended Baryon Oscillation Spectroscopic Survey, it maps galaxies and quasars from when the universe was 3 to 8 billion years young! This period helps scientists understand dark energy and how it affects the expansion of the universe.
Together, these surveys in the latest phase of the SDSS produced an extremely detailed map of the universe, covering nearby and very far away structures.
SDSS Plates
To capture the spectra of millions of objects, scientists had to come up with an efficient way of collecting data of many objects at the same time. That’s how the Plates were born. You can learn more about plates and spectra in the next sections.
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All image credits to SDSS