Sachs-Wolfe effect Sacramento Peak Observatory Sagitta Sagittarius Sagittarius A Sagittarius Arm Sagittarius B Saha equations Sail Salpeter function Salpeter process Salyut SAO SAO Star Catalog SAR saros saros series SAS satellite satellite galaxy satellite laser ranging Saturn Saturn Nebula Scales scattering Scheat Schedar Schickard Schmidt camera Schmidt-Cassegrain telescope Schönberg-Chandrasekhar limit Schröter's effect Schröter's Valley Schwarzschild metric Schwarzschild radius Schwassmann-Wachmann 1, Comet scintillation scintillation counter scopulus Scorpio Scorpion Scorpius Scorpius X-1 Sculptor Sculptor's Workshop Scutum S Doradus star Sea Goat Sea Monster Seashell Galaxy season second second contact secular secular acceleration secular parallax sedimentary rock seeing selenocentric selenography selenology semidetached system semimajor axis semiregular variable separation Serpens Serpent Serpent Bearer Serrurier system SEST SETI setting circles Seven Sisters Sextans Sextant Seyfert galaxy Seyfert's Sextet shadow bands Shapley-Ames Catalog Shaula shell star Shemakha Astrophysical Observatory shepherd satellites shergottite Shield shield volcano Ship shock wave shooting star short-period comet short-period variable Sickle side-lobe sidereal sidereal day sidereal month sidereal period sidereal rate sidereal time sidereal year Sidereus nuncius siderite siderolite siderostat Siding Spring Observatory Siegena Sikhote-Alin shower silicate silicon star SIMBAD singularity Sinope sinus Sirius Sirrag SIRTF Sisyphus Skylab SLR Small Astronomy Satellites small circle Small Magellanic Cloud small molecular cloud Smithsonian Astrophysical Observatory SMM SN 1987A SNC meteorite Sobieski's Shield Socorro SOFIA soft gamma repeater SOHO Sojourner sol solar Solar-A solar activity Solar and Heliospheric Observatory solar apex solar constant solar corona solar cycle solar day solar eclipse solar flare Solar Maximum Mission solar nebula solar prominence solar system solar time solar tower solar wind Solis Planum solstices solstitial colure Sombrero galaxy Sonneberg Observatory source source count South African Astronomical Observatory South Atlantic anomaly Southern Cross Southern Crown Southern Fish Southern Pleiades Southern Triangle southing Soyuz space Space Infrared Telescope Facility Spacelab space research Space Shuttle space telescope Space Telescope Science Institute spacetime Spacewatch space weather Special Astrophysical Observatory Special Relativity speckle interferometry spectral class spectral index spectral line spectral type spectrogram spectrograph spectroheliogram spectroheliograph spectrometer spectroscope spectroscopic binary spectroscopy spectrum spherical aberration spherical space Spica spicules spider spin casting Spindle Galaxy spiral galaxy sporadic meteor Spörer's law s-process spur Sputnik Square of Pegasus SS433 S star SS Cygni star star star atlas starburst galaxy star catalogue star cloud star cluster star diagonal Stardust starquake star tracker star trail stationary point statistical parallax steady-state metric steady-state theory stellar Stellar Data Centre stellar evolution stellar populations stellar wind Stephan's Quintet Stern Sternberg State Astronomical Institute Steward Observatory Stickney Stokes parameters Stonehenge Stonyhurst disc stony-iron meteorite stony meteorite stratigraphy stratosphere strewn field string theory Strömgren radius Strömgren sphere S-type asteroid Subaru Telescope subdwarf sub-Earth point subgiant submillimetre-wave astronomy subreflector sub-solar point sulci Summer Triangle Sun sundial sundog Sunflower Galaxy sungrazer sunrise sunset sunspot Sunspot Sunyaev-Zel'dovich effect supercluster SuperCOSMOS supergalactic plane supergiant supergranulation supergravity superior conjunction superior culmination superior planet Super-Kamiokande superluminal motion supermassive star supernova Supernova 1987A supernova remnant superstring theory surface gravity surge Surveyor SU Ursae Majoris star Swan Swan Nebula Swedish-ESO Submillimetre Telescope Swordfish Sword Handle Sword of Orion Sylvia symbiotic stars synchronous rotation synchrotron radiation synodic month synodic period synthetic aperture radar Syrtis Major Planum syzygy