[{"n": "Saros (astronomy)", "u": "/e/astronomical-concepts-and-techniques/saros-astronomy/", "s": "An eclipse cycle of 223 synodic months (about 18 years 11 days 8 hours) used to predict nearly identical solar"}, {"n": "Selenography", "u": "/e/astronomical-concepts-and-techniques/selenography/", "s": "The study of the Moon's surface and physical features."}, {"n": "Sidereal time", "u": "/e/astronomical-concepts-and-techniques/sidereal-time/", "s": "Timekeeping system based on Earth's rotation relative to the fixed stars."}, {"n": "Sky brightness", "u": "/e/astronomical-concepts-and-techniques/sky-brightness/", "s": "The measure of the sky's scattered and diffused light, from day to darkest night."}, {"n": "Solar cycle", "u": "/e/astronomical-concepts-and-techniques/solar-cycle/", "s": "An 11-year periodic change in solar activity and sunspot numbers."}, {"n": "Solstice", "u": "/e/astronomical-concepts-and-techniques/solstice/", "s": "Twice-yearly event when the Sun's declination appears to stand still."}, {"n": "Space weather", "u": "/e/astronomical-concepts-and-techniques/space-weather/", "s": "Study of solar wind effects on the Solar System."}, {"n": "Space physics", "u": "/e/astronomical-concepts-and-techniques/space-physics/", "s": "Study of natural plasmas in Earth's upper atmosphere and Solar System."}, {"n": "Spectral energy distribution", "u": "/e/astronomical-concepts-and-techniques/spectral-energy-distribution/", "s": "A plot of energy versus frequency or wavelength used in astronomy."}, {"n": "Spectral index", "u": "/e/astronomical-concepts-and-techniques/spectral-index/", "s": "A measure of flux density's dependence on frequency."}, {"n": "Spherical astronomy", "u": "/e/astronomical-concepts-and-techniques/spherical-astronomy/", "s": "Oldest branch of astronomy, locating objects on the celestial sphere."}, {"n": "Stellar parallax", "u": "/e/astronomical-concepts-and-techniques/stellar-parallax/", "s": "Trigonometric method for measuring distances to nearby stars."}, {"n": "Surface brightness", "u": "/e/astronomical-concepts-and-techniques/surface-brightness/", "s": "Surface brightness measures extended object visibility per angular area."}, {"n": "Time-domain astronomy", "u": "/e/astronomical-concepts-and-techniques/time-domain-astronomy/", "s": "Study of how astronomical objects change with time."}, {"n": "Tip of the red-giant branch", "u": "/e/astronomical-concepts-and-techniques/tip-of-the-red-giant-branch/", "s": "A standard candle using the brightest red-giant-branch stars."}, {"n": "Tropical year", "u": "/e/astronomical-concepts-and-techniques/tropical-year/", "s": "Time for Sun to return to same seasonal position."}, {"n": "Twinkling", "u": "/e/astronomical-concepts-and-techniques/twinkling/", "s": "Twinkling is atmospheric scintillation affecting distant light sources."}, {"n": "Umbra, penumbra and antumbra", "u": "/e/astronomical-concepts-and-techniques/umbra-penumbra-and-antumbra/", "s": "Three distinct parts of a shadow from an opaque object."}, {"n": "Velocity dispersion", "u": "/e/astronomical-concepts-and-techniques/velocity-dispersion/", "s": "Statistical spread of velocities in astronomical groups."}, {"n": "UBV photometric system", "u": "/e/astronomical-concepts-and-techniques/ubv-photometric-system/", "s": "First standardized photometric system for stellar classification."}, {"n": "Zodiac", "u": "/e/astronomical-concepts-and-techniques/zodiac/", "s": "A celestial coordinate system dividing the ecliptic into 12 signs."}, {"n": "Zodiacal light", "u": "/e/astronomical-concepts-and-techniques/zodiacal-light/", "s": "A faint glow of sunlight scattered by interplanetary dust."}]