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Sloan Digital Sky Survey
The Sloan Digital Sky Survey (SDSS) is a long-running astronomical survey that has imaged and taken spectra of millions of stars, galaxies, and quasars since 1998.
Sloan Great Wall
The Sloan Great Wall is a vast filament of galaxies about a billion light-years from Earth, identified in 2003 by J. Richard Gott III and Mario Jurić as then the largest known structure.
Slow-roll parameters
Slow-roll parameters are small dimensionless quantities measuring how slowly the inflaton field driving cosmic inflation changes as the universe expands; inflation ends where the first parameter reaches 1.
SMICA
SMICA (Spectral Matching Independent Component Analysis) is a blind, spectral-domain method introduced in 2003 for separating the cosmic microwave background from foreground emissions, and one of Planck's four component-separation pipelines.
Solar telescope
A solar telescope is an optical telescope specialized for observing the Sun, managing intense heat and light while resolving fine structure in the solar atmosphere.
Solstice
A solstice is one of the two yearly moments when the Sun reaches its greatest distance north or south of the celestial equator, around June 21 and December 21.
Sound horizon
The sound horizon is the distance sound waves traveled in the primordial plasma before recombination, about 147 Mpc, surviving as the baryon acoustic oscillation scale.
South Pole Telescope
The South Pole Telescope (SPT) is a 10-meter microwave and millimeter-wavelength telescope at Amundsen–Scott Station at the geographic South Pole, operating since 2007. It surveys galaxy clusters and maps the cosmic microwave background.
Space animal hypothesis
The space animal hypothesis proposes that some UFOs are living organisms native to Earth's atmosphere or space rather than spacecraft, first argued by John Philip Bessor in 1947.
Speckle interferometry
Speckle interferometry is an astronomical technique introduced by Antoine Labeyrie in 1970 that recovers diffraction-limited resolution from ground-based telescopes by analyzing thousands of very short exposures, and is widely used to measure binary stars.
Spectral index (cosmology)
The scalar spectral index, ns, is the exponent describing how the amplitude of primordial density fluctuations depends on scale, measured near 0.965 and seen as key evidence for cosmic inflation.
Spectroscopic redshift
A spectroscopic redshift is the displacement of a star's, galaxy's, or quasar's spectral lines from their rest wavelengths, expressed as z and about ten times more precise than photometric redshifts.
Spektr-R
Spektr-R, also known as RadioAstron (Спектр-Р), was a Russian orbital observatory carrying a 10-meter radio telescope that operated from 2011 to 2019, pairing with ground telescopes for interferometry.
Spitzer Space Telescope
The Spitzer Space Telescope, also called SIRTF, was a NASA infrared observatory launched in 2003 and decommissioned in 2020, best known for revealing seven Earth-size planets around TRAPPIST-1.
SPT-3G
SPT-3G is the third-generation millimeter-wavelength camera on the 10-meter South Pole Telescope in Antarctica, installed in January 2017 with about 16,000 detectors to map the cosmic microwave background's temperature and polarization.
Standard candle
A standard candle is an astronomical object whose known intrinsic luminosity, compared with its apparent brightness, yields its distance; examples include Cepheids and Type Ia supernovae.
Standard siren
A standard siren is an astronomical source, typically a merging compact binary, whose gravitational-wave signal directly encodes its distance, allowing measurements of the Hubble constant.
STARE2
STARE2 (Survey for Transient Astronomical Radio Emission 2) is a network of three low-cost radio receivers in the southwestern United States, built by Caltech to detect fast radio bursts.
Starobinsky inflation
Starobinsky inflation is a model of cosmic inflation in which the Universe's early expansion is driven by an added R² term in gravity, proposed by Alexei Starobinsky in 1980.
Starshade
A starshade is a proposed flower-shaped spacecraft flying tens of thousands of kilometers ahead of a space telescope to block starlight, enabling direct imaging of planets.
Stellar occultation
Stellar occultation is an observational technique in which starlight passing behind a solar system body is analyzed, revealing atmospheric profiles and ring structure at kilometer scales.
Stochastic gravitational-wave background
The stochastic gravitational-wave background (SGWB, often GWB) is a random gravitational-wave signal from many weak, unresolved sources, with pulsar timing arrays reporting evidence in 2023.
Subaru Telescope
The Subaru Telescope, originally named the Japan National Large Telescope, is an 8.2-meter optical-infrared telescope on Maunakea in Hawaiʻi, operated by Japan and opened for use in 2000.
Submillimeter Array
The Submillimeter Array (SMA) is an eight-antenna radio interferometer near the summit of Maunakea in Hawaiʻi that observes at submillimeter wavelengths and joined the Event Horizon Telescope's first black hole images.
Sultan bin Salman Al Saud (سلطان بن سلمان آل سعود)
Sultan bin Salman Al Saud, known as Sultan bin Salman, is a Saudi prince and pilot who became the first Arab and first Muslim in space aboard Discovery in 1985.
Sunyaev–Zel'dovich effect
The Sunyaev–Zel'dovich effect is the distortion of the cosmic microwave background when its photons scatter off hot electrons in galaxy clusters; predicted in the 1970s, it finds clusters independently of distance.
Super-Earth
A super-Earth, sometimes called a superterran, is an exoplanet more massive than Earth but lighter than Neptune, up to about 10 Earth masses, and may be rocky, water-rich, or gas-dominated.
Super-Kamiokande (スーパーカミオカンデ)
Super-Kamiokande (スーパーカミオカンデ), or Super-K, is the world's largest water Cherenkov neutrino detector, located 1,000 meters underground in Gifu, Japan; its evidence for neutrino oscillations earned Nobel Prizes in 2002 and 2015.
Superfluid dark matter
Superfluid dark matter is a theoretical model proposed in 2015 by Lasha Berezhiani and Justin Khoury, in which dark matter condenses into a superfluid inside galaxies.
Supernova Cosmology Project
The Supernova Cosmology Project is a Berkeley Lab collaboration led by Saul Perlmutter that announced in 1998 the first evidence that the universe's expansion is accelerating.