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- S AntliaeS Antliae is a W Ursae Majoris-type eclipsing binary star in Antlia.
- S OrionisS Orionis is an asymptotic giant branch star in the constellation Orion, approximately 480
- S-processNucleosynthesis pathway
- S-type asteroidAsteroid spectral type indicating stony composition
- S-type starType of cool giant star
- S. M. Razaullah AnsariIndian Scientist (1932–2023)
- S5 0014+81S5 0014+81 is a distant, compact, hyperluminous, broad-absorption-line quasar, or blazar,
- Sachs–Wolfe effectThe Sachs–Wolfe effect, named after Rainer K. Sachs and Arthur M. Wolfe, is a property of
- Safronov RegioSafronov Regio (formerly Krun Macula) is the westernmost of the "Brass Knuckles", a series
- SagittaConstellation in the northern celestial hemisphere
- Sagittarius (astrology)Ninth astrological sign of the zodiac
- Sagittarius (constellation)Zodiac constellation in the southern celestial hemisphere
- Sagittarius ARadio source at center of the Milky Way
- Sagittarius A*Supermassive black hole at the center of the Milky Way
- Sagittarius B2Molecular cloud
- Sagittarius Dwarf Spheroidal GalaxySatellite galaxy of the Milky Way
- SaltfjelletSaltfjellet is a mountain area in Nordland county, Norway that separates the two regions o
- Sample-return missionSpacecraft mission
- San Augustin MountainsThe San Augustin Mountains are a small mountain subrange located at the southern terminus
- Santa Cruz, CaliforniaCity in California, United States
- Sarah BridleBritish astrophysicist
- Sarah HörstAmerican planetary scientist
- Saros (astronomy)Length of time after which an eclipse repeats
- Satellite Catalog NumberNORAD satellite identifier
- Satellite galaxies of the Milky WayGalaxies bound to the Milky Way
- Satellite galaxyGalaxy that orbits a larger galaxy due to gravitational attraction
- Satellite system (astronomy)Set of gravitationally bound objects in orbit
- Satu SuroSatu Suro (Javanese: ꦱꦶꦗꦶꦱꦸꦫ, Siji Suro) is the first day of the Javanese calendar year in
- SaturnSixth planet from the Sun
- Saturn in fictionDepictions of the planet
- Saturn's hexagonCloud pattern on the planet Saturn
- Savelli, CalabriaSavelli is a comune and town in the province of Crotone, in Calabria, southern Italy, loca
- Scalar curvatureMeasure of curvature in differential geometry
- Scale factor (cosmology)Expansion of the universe parameter
- Scale heightDistance over which a quantity decreases by a factor of e
- Scattered discCollection of bodies in the extreme Solar System
- Schelte J. BusAmerican astronomer
- Schmidt cameraAstrophotographic telescope
- Schwarzschild radiusRadius of the event horizon of a Schwarzschild black hole
- Scorpio (astrology)Eighth astrological sign of the zodiac
- ScorpiusZodiac constellation in the southern celestial hemisphere
- Scorpius X-1Astronomical X-ray source
- ScotobiologyScotobiology is the study of biology as directly and specifically affected by darkness, as
- Scott ForbushScott Ellsworth Forbush (April 10, 1904 – April 4, 1984) was an American astronomer, physi
- Scott Jay KenyonScott Jay Kenyon (born 1956) is an American astrophysicist. His work has included advances
- Sculptor (constellation)Constellation in the southern celestial hemisphere
- Sculptor Dwarf GalaxyDwarf spheroidal Galaxy in the constellation Sculptor
- Sculptor Dwarf Irregular GalaxyThe Sculptor Dwarf Irregular Galaxy (SDIG) is an irregular galaxy in the constellation Scu
- Sculptor GalaxyIntermediate spiral galaxy in the constellation Sculptor
- Scutum (constellation)Small constellation in the southern celestial hemisphere
- Scutum–Centaurus ArmSpiral arm of the Milky Way
- Sea saltSalt produced from the evaporation of seawater
- Search for extraterrestrial intelligenceEffort to find civilizations not from Earth
- Seatbelt basaltLunar Sample 15016, better known as the "Seatbelt Basalt", is a lunar sample discovered an
- Sebastian F. HönigGerman astronomer
- Secondary craterSecondary craters are impact craters formed by the ejecta that was thrown out of a larger
- Secular variationLong-term non-periodic variation
- Sedna (dwarf planet)Distant body in the outer Solar System
- SednoidGroup of trans-Neptunian objects
- Seiji UedaJapanese astronomer
- SelenographyStudy of the surface and shape of the Moon
- Self-gravitationGravitational force holding a body or system of bodies together
- Semi-major and semi-minor axesTerm in geometry; longest and shortest semidiameters of an ellipse
- SemicircleGeometric shape
- Semion BraudeSemion Yakovlevich Braude (Ukrainian: Семен Якович Брауде; 28 January 1911 – 29 June 2003)
- Semiregular variable starType of variable star
- Sentinel Space TelescopeThe Sentinel Space Telescope was a space observatory to be developed by Ball Aerospace & T
- Sentry (monitoring system)JPL program to monitor the Minor Planet Center's catalog for Earth impacts
- September equinoxWhen sun appears directly over equator
- SerpensConstellation split into two non-contiguous parts
- Serpens SouthThe Serpens South star cluster is a relatively dense group of more than 600 young stars, d
- Seth Carlo ChandlerAmerican astronomer (1846–1913)
- Setting (narrative)Aspect of literature
- SextansConstellation on the celestial equator
- Seyfert galaxyClass of active galaxies with very bright nuclei
- Shackleton (crater)Lunar impact crater
- Shakespeare quadrangleThe Shakespeare quadrangle is a region of Mercury running from 90 to 180° longitude and 20
- Shape of the universeLocal and global geometry of the universe
- Shapley SuperclusterSupercluster in the constellation Centaurus
- Sherburne Wesley BurnhamAmerican astronomer
- Sheshan ObservatoryThe Sheshan Observatory (Chinese: 佘山天文台; pinyin: Shéshān tiānwéntái) is an observatory on
- Sidereal timeTimekeeping system on Earth relative to the celestial sphere
- Sidereal yearTime taken by the Earth to orbit the Sun once with respect to the fixed stars
- Sidereus NunciusAstronomical treatise of Galileo
- Sidewalk astronomySidewalk astronomy or street corner astronomy refers to the activity of setting up a teles
- Siding Spring ObservatoryAstronomic observatory in New South Wales, Australia
- Siding Spring SurveyObservatory
- Sierra de Los FilabresSierra de Los Filabres is the largest mountain range in Almería Province, Andalusia, Spain
- Sigma ScorpiiSigma Scorpii (or σ Scorpii, abbreviated Sigma Sco or σ Sco), is a multiple star system in
- SIMBADFrench astronomical database
- Simeiz ObservatoryFormer observatory on Kosh-Kaya, Crimea
- Simply connected spaceIn topology, a topological space is called simply connected (or 1-connected, or 1-simply c
- Sinus MeridianiSinus Meridiani (Latin Sinus meridiani, "Meridian Bay") is an albedo feature on Mars stret
- Sir Arthur Clarke AwardThe Sir Arthur Clarke Award is a British award given annually since 2005 in recognition of
- SiriusBrightest star in Earth's night sky
- Sirius BClosest known white dwarf star to Earth
- Sixth Cambridge Survey of Radio SourcesThe 6C Survey of Radio Sources (6C) is an astronomical catalogue of celestial radio source
- Sky brightnessVisual perception of the sky and how it scatters and diffuses light
- Sky gazing (Dzogchen)In Dzogchen, sky gazing (Wylie: nam mkha' ar gtad, THDL: namkha arté) is one of the core p
- Sky-Sailor2004 proposal of a robotic Mars aircraft
- SkyglowDiffuse luminance of the night sky
- SkyMapperSkyMapper is a fully automated 1.35 m (4.4 ft) wide-angle optical telescope at Siding Spri
- Slidr SulciTectonic fault on Triton
- Sloan Digital Sky SurveyMulti-spectral imaging and spectroscopic redshift survey
- Slowly pulsating B-type starA slowly pulsating B-type star (SPB), formerly known as a 53 Persei variable, is a type of
- Small Astronomy Satellite 2The Small Astronomy Satellite 2, also known also as SAS-2, SAS B or Explorer 48, was a NAS
- Small Magellanic CloudDwarf irregular galaxy, satellite galaxy of the Milky Way
- Smithsonian Astrophysical ObservatoryThe Smithsonian Astrophysical Observatory (SAO) is a research institute of the Smithsonian
- SN 1006Supernova observed from Earth in 1006
- SN 1054Supernova in the constellation Taurus; visible from 1054 to 1056
- SN 1572Supernova in the constellation Cassiopeia
- SN 1885A1885 supernova in the Andromeda Galaxy
- SN 1972ESupernova in the NGC 523 galaxy, first observed in 1972
- SN 1979CSupernova of 1979 in the constellation Coma Berenices
- SN 1987A1987 supernova event in the constellation Dorado
- SN 2003fgUnusual Type Ia supernova in the constellation Böotes
- Sobral, CearáSobral is a municipality in the state of Ceará, Brazil.
- Socorro, New MexicoCity in New Mexico, United States
- Solar analogStar that is particularly similar to the Sun
- Solar coreCentral region of the Sun
- Solar coronaOutermost layer of the Sun's atmosphere
- Solar cyclePeriodic change in the Sun's activity
- Solar cycle 20Solar cycle 20 was the twentieth solar cycle since 1755, when extensive recording of solar
- Solar cycle 22Solar cycle 22 was the 22nd solar cycle since 1755, when extensive recording of solar suns
- Solar deitySky deity who represents the Sun
- Solar dynamoThe solar dynamo is a physical process that generates the Sun's magnetic field. It is expl
- Solar eclipseEvent wherein the Sun is obscured by the Moon
- Solar eclipse of August 1, 2008Total eclipse
- Solar eclipse of August 11, 1999Eclipse over Europe and Asia
- Solar eclipse of August 21, 2017Total eclipse visible from the mainland US
- Solar eclipse of December 4, 2002Total eclipse
- Solar eclipse of June 21, 2001Total eclipse
- Solar eclipse of March 29, 2006Total eclipse
- Solar eclipse of May 29, 1919Total eclipse, which helped prove Einstein's theory of relativity
- Solar eclipse of November 23, 2003Total eclipse
- Solar eclipses on MarsThe two moons of Mars, Phobos and Deimos, are much smaller than Earth's Moon, greatly redu
- Solar eclipses on the MoonLunar phenomenon wherein the Sun is obscured by Earth
- Solar energetic particlesHigh-energy particles from the Sun
- Solar flareEruption of electromagnetic radiation
- Solar maximumRegular period of greatest solar activity
- Solar minimumRegular period of least solar activity
- Solar neutrinoExtremely light particle produced by the Sun
- Solar particle eventSolar phenomenon
- Solar phenomenaNatural phenomena within the Sun's atmosphere
- Solar radio emissionRadio waves produced by the Sun
- Solar Saros 126Saros cycle series 126 for solar eclipses occurs at the Moon's descending node, repeating
- Solar Saros 127Saros cycle series 127 for solar eclipses occurs at the Moon's ascending node, repeating e
- Solar Saros 142Saros cycle series 142 for solar eclipses occurs at the Moon's descending node, repeating
- Solar Saros 145Saros cycle series 145 for solar eclipses occurs at the Moon's ascending node, repeating e
- Solar Saros 152Saros cycle series 152 for solar eclipses occurs at the Moon's descending node, repeating
- Solar stormDisturbance on the Sun
- Solar SystemPlanetary system consisting of the Sun and objects orbiting it
- Solar transition regionThe solar transition region is a region of the Sun's atmosphere between the upper chromosp
- Solar windStream of charged particles from the Sun
- Solo operations of Apollo 15During the 1971 Apollo 15 mission to the Moon, and its three days of exploration on the lu
- Solon Irving BaileyAmerican astronomer (1854–1931)
- SolsticeTwice-annual astronomical event when the Sun is farthest from above the Earth's equator
- Sombrero GalaxyGalaxy in the constellation Virgo
- Sōtatsu (crater)Sōtatsu is a crater on Mercury. Its name was adopted by the IAU in 1976, after the Japanes
- Sounding rocketRocket designed to take measurements during its flight
- South Pole WallMassive cosmic structure
- South Pole–Aitken basinLarge impact crater on the Moon
- Southern celestial hemisphereSouthern half of the celestial sphere
- Southwest Research InstituteApplied research and development nonprofit organization in Texas, USA
- Soviet crewed lunar programsPrograms by the Soviet Union to land humans on the Moon
- Space Exploration InitiativeThe Space Exploration Initiative was a 1989–1993 space public policy initiative of the Geo
- Space Launch SystemNASA super heavy-lift expendable launch vehicle used in the Artemis Program
- Space Launch System (Turkey)The Space Launch System (Turkish: Uydu Fırlatma Sistemi), shortly UFS, is a project to dev
- Space lawLaw governing activities in outer space
- Space NetworkSpace Network (SN) is a NASA program that combines space and ground elements to support sp
- Space physicsStudy of space plasmas in the Solar System
- Space rendezvousSeries of orbital maneuvers
- Space Telescope Science InstituteScience operations center operated by NASA
- Space weatherBranch of space physics and aeronomy
- Spacecraft propulsionMethod used to accelerate spacecraft
- SpacewatchAstronomical survey that specializes in the study of minor planets
- Spaceway-3Spaceway-3 is a communications satellite which was launched on August 14, 2007, at 23:44:0
- SpaceX CRS-1SpaceX CRS-1, also known as SpX-1, was SpaceX's first operational cargo mission to the Int
- SpaceX StarshipReusable superheavy-lift general-purpose launch vehicle
- Specific orbital energyParameter in the gravitational two-body problem
- Spectral energy distributionPlot of energy and frequency or wavelength
- Spectral indexMeasure in astronomy
- Spectro-Polarimetric High-Contrast Exoplanet ResearchSpectro-Polarimetric High-contrast Exoplanet REsearch (VLT-SPHERE) is an adaptive optics s
- SPECULOOSSPECULOOS (Search for habitable Planets EClipsing ULtra-cOOl Stars) is a project consistin
- Sphere of influence (astrodynamics)Region of space gravitationally dominated by a given body
- Spherical astronomyBranch of astronomy about the celestial sphere
- SpheroidSurface formed by rotating an ellipse
- SpicaStar in the constellation Virgo
- SpiralCurve that winds around a central point
- Spiral galaxyClass of galaxy that has spiral structures extending from their cores
- Spiral Galaxy (sculpture)Spiral Galaxy is an outdoor stainless steel sculpture by John David Mooney, installed outs
- Spite plateauBaseline of stellar lithium abundance
- Spur (lunar crater)Spur is a feature on Earth's Moon, a crater in the Hadley–Apennine region. Astronauts Davi
- Sputnik PlanitiaSputnik Planitia (formerly Sputnik Planum) is a large, partially glaciated basin on Pluto.
- Squam LakeSquam Lake is a lake located in the Lakes Region of central New Hampshire, United States,
- SSPSF modelModel of star formation
- Standard asteroid physical characteristicsAstronomical parameters
- Stanislav George DjorgovskiAmerican scientist
- StarLarge self-illuminated object in space
- Star catalogueAstronomical catalogue that lists stars and their positions in the sky
- Star clusterGroup of stars
- Star formationGravitational process studied in astronomy
- Star systemSmall number of stars that orbit each other
- Starburst galaxyGalaxy undergoing an exceptionally high rate of star formation
- Starburst regionRegion of faster than normal star formation
- StarlightLight from the stars
- StarspotStellar phenomenon
- Steady-state modelModel of the universe – alternative to the Big Bang model
- Stellar associationLoose star cluster
- Stellar atmosphereOuter region of the volume of a star
- Stellar black holeBlack hole formed by a collapsed star
- Stellar chemistryStellar chemistry is the study of chemical composition of astronomical objects; stars in p
- Stellar classificationClassification of stars based on spectral properties
- Stellar collisionComing together of two stars
- Stellar coreRegion at the center of a star
- Stellar coronaOutermost layer of a star's atmosphere
- Stellar designations and namesProcess by which stars are named
- Stellar dynamicsBranch of astrophysics
- Stellar evolutionChanges to stars over their lifespans
- Stellar haloStar-containing portion of a galactic halo
- Stellar kinematicsStudy of the movement of stars
- Stellar magnetic fieldMagnetic field generated inside a star
- Stellar massMass of a star in astronomy
- Stellar mass lossPhysical phenomenon of stars
- Stellar nucleosynthesisCreation of chemical elements within stars
- Stellar parallaxChanged position of star vs background
- Stellar pulsationStellar pulsations are caused by expansions and contractions in the outer layers as a star
- Stellar rotationAngular motion of a star about its axis
- Stellar structureStructure of stars
- Stellar windFlow of gas ejected from the upper atmosphere of a star
- Stephenson 2Stephenson 2, also known as RSGC2 (Red Supergiant Cluster 2), is a young massive open clus
- StereopsisVisual sensation of spatial awareness
- Stereopsis (fungus)Stereopsis is the sole genus of fungi in the family Stereopsidaceae. The genus was formerl
- Steven BalbusAmerican astrophysicist (born 1953)
- Steven J. DickAmerican astronomer and author (born 1949)
- Steven J. OstroSteven Jeffrey Ostro (March 9, 1946 – December 15, 2008) was an American scientist special
- StockelsdorfStockelsdorf is a municipality in the district of Ostholstein, in Schleswig-Holstein, Germ
- Stolen and missing Moon rocksOf the 270 Apollo 11 Moon rocks and the Apollo 17 Moon rocks (dubbed the Goodwill rocks) t
- Strong gravitational lensingGravitational deflection of light
- Structure formationAstrophysical models for the formation of galaxies and clusters of galaxies
- STS-61-FSTS-61-F was a NASA Space Shuttle mission planned to launch on 15 May 1986 using Challenge
- Styx (moon)Small natural satellite of Pluto
- SU Ursae MajorisSU Ursae Majoris, or SU UMa, is a close binary star in the northern circumpolar constellat
- Su-Shu HuangSu-Shu Huang (黃授書, April 16, 1915 – September 15, 1977) was a Chinese-born American astrop
- Sub-brown dwarfAstronomical objects of planetary size that did not form in orbit around a star
- Sub-NeptunePlanet smaller than Neptune with a low density envelope
- SubdwarfStar of luminosity class VI under the Yerkes spectral classification system
- SubgiantType of star larger than main-sequence but smaller than a giant
- Submillimetre astronomyAstronomy with terahertz (< 1 mm)-range light
- Substellar objectAstronomical object without the mass to sustain hydrogen fusion
- SubstormShort term magnetosphere disturbance
- Subsynchronous orbitA subsynchronous orbit is an orbit of a satellite that is nearer the planet than it would
- Summer solsticeAstronomical phenomenon time
- Summer TriangleAsterism
- SunStar at the centre of the Solar System
- Sun pathArc-like path that the Sun appears to follow across the sky
- Sun-synchronous orbitType of geocentric orbit
- Sungrazing cometComet that is extremely close to the sun during part of its orbit
- SunriseTime of day when the sun appears above the horizon
- SunsetDaily falling of the Sun below the horizon
- SunspotTemporary spots on the Sun's surface
- Super star clusterType of very massive young open cluster thought to be the precursor of a globular cluster
- Super-EarthType of exoplanet larger than Earth
- SuperbubbleCavity hundreds of light years across created by strong stellar winds in a galaxy
- SuperclusterLarge group of smaller galaxy clusters or galaxy groups
- SupergiantType of star that is massive and luminous
- Superluminal motionApparent faster-than-light motion of distant astronomical objects
- Superluminous supernovaSupernova at least ten times more luminous than a standard supernova
- Supermassive black holeLargest type of black hole
- SupermoonFull or new moon which appears larger
- SupernovaAstrophysical phenomenon
- Supernova nucleosynthesisProduction of the elements in a supernova explosion
- Supernova remnantRemnants of an exploded star
- Supersynchronous orbitA supersynchronous orbit is either an orbit with a period greater than that of a synchrono
- Surface brightnessAstronomical term for luminosity per area
- Surface gravityStandard surface gravity
- Svetlana GerasimenkoSoviet and Tajikistani astronomer (1945–2025)
- SW Sextantis variableSW Sextantis variable stars are a kind of cataclysmic variable star; they are double-star
- SWAP (instrument)The Sun Watcher using Active Pixel System Detector and Image Processing (SWAP) telescope i
- Swedish-ESO Submillimetre TelescopeThe Swedish-ESO Submillimetre Telescope (SEST) is a 15-metre diameter radio telescope. It
- SWEEPS-04SWEEPS-04 is an extrasolar planet orbiting the star SWEEPS J175853.92−291120.6 in the cons
- SX Arietis variableSX Arietis variables are a class of variable stars. They are generally B-type main sequenc
- SX Phoenicis variableAn SX Phoenicis variable is a type of variable star. These stars exhibit a short period pu
- Sycorax (moon)Sycorax is the largest irregular satellite of Uranus. It was discovered in September, 1997
- Symbiotic novaSymbiotic novae are slow irregular eruptive variable stars with very slow nova-like outbur
- Synodic dayRotation period of a body relative to the primary object it orbits, e.g. solar day
- Syzygy (astronomy)Alignment of celestial bodies
