Taien calendar (Taien-reki): an early Japanese lunisolar calendar Taien calendar Taien (Taien-reki or Dayan) was a Japanese lunisolar calendar of Chinese origin used in Japan from about 746 to 857. It regulated months, intercalation and official dates in the Na…
Taiyo (satellite) Taiyo was an early Japanese scientific satellite launched by the Institute of Space and Astronautical Science (University of Tokyo) on 24 February 1975; it reentered and burned up…
Tansei — Japan's second artificial satellite Tansei Tansei (Tonsei) was Japan's second artificial satellite, launched by the University of Tokyo's ISAS on 16 February 1971. The name means "light blue," reflecting the university's sc…
Tarantula Nebula (30 Doradus) Tarantula nebula A massive H II region in the Large Magellanic Cloud, the Tarantula Nebula (30 Doradus) is the Local Group’s most active starburst region, hosting NGC 2070 and R136 and known for Su…
Tarqeq (Saturn LII): a small prograde irregular moon of Saturn Tarqeq (moon) Tarqeq (Saturn LII, S/2007 S 1) is a small, non-spherical prograde irregular satellite of Saturn discovered in 2007. It belongs to the Inuit group and orbits at about 17.9 million…
Tarvos (Saturnian moon) Tarvos (moon) Tarvos (Saturn XXI) is a small irregular moon of Saturn discovered in 2000. It orbits far from the planet and belongs to the Gallic group, likely a fragment of a larger body such a…
Tatooine: Desert Planet and Cultural Setting in the Star Wars Galaxy Tatooine Overview of Tatooine, the arid binary‑sun desert planet in Star Wars: its harsh environment, settlements and cultures, role in Anakin and Luke Skywalker’s lives, and its criminal u…
Tau Ceti — Nearby Sun-like Star with Debris Disk and Planet Candidates Tau Ceti Tau Ceti is a nearby, Sun-like star in Cetus visible to the naked eye. It is slightly smaller and metal-poor, surrounded by a substantial dust disk and hosts multiple candidate pla…
Taurus (astrology): the Bull — earth sign, fixed modality, ruled by Venus Taurus (astrology) Taurus is the second zodiac sign, symbolized by the Bull. An earth sign with a fixed modality and ruled by Venus, it connotes steadiness, sensuality and material concerns. Dates di…
Taurus (constellation): overview, notable objects, history and observing Taurus (constellation) Taurus is a northern zodiac constellation notable for Aldebaran, the Hyades and Pleiades open clusters, and the Crab Nebula; prominent in myth, navigation and astronomical study.
Taygete (Jupiter moon) Taygete (moon) Taygete is a small, irregular retrograde moon of Jupiter discovered in 2000. It orbits far from the planet, belongs to a retrograde group, and is thought to be a captured asteroid…
Telescope: principles, history, types, and uses Telescope Comprehensive overview of telescopes: how they collect light, major designs, history from the 17th century, types across the electromagnetic spectrum, mounts, amateur use and notab…
Telescopium (constellation) Telescopium Telescopium is a small, faint constellation of the southern sky introduced in the 18th century. Named for the telescope, it is one of the 88 modern constellations and contains seve…
Telesto — a Trojan moon of Saturn Telesto (moon) Telesto is a small, icy Trojan moon sharing Tethys’s orbit at the leading L4 point. Discovered in 1980 from telescopic observations, it has a smooth, low-density surface and was im…
Tempel 1 (9P/Tempel): discovery, Deep Impact encounter, and scientific legacy Tempel 1 Tempel 1 is a short-period comet discovered in 1867. NASA's Deep Impact probe struck it in 2005, revealing insights into cometary composition, structure and the presence of exposed…
Tenma (ASTRO-B): Japan's second X‑ray astronomy satellite Tenma Tenma (ASTRO‑B) was Japan's second dedicated X‑ray astronomy satellite, launched in 1983 by ISAS/University of Tokyo to observe cosmic X‑ray sources and advance high‑energy astroph…
Terraforming: altering planets and moons to support Earth life Terraforming Terraforming is the theoretical engineering of a planet or moon to make it habitable for terrestrial organisms, via changes to atmosphere, temperature, water and ecosystems.
Tethys — Saturn's icy mid-sized moon Tethys (moon) Tethys is a bright, water-ice–rich moon of Saturn noted for the huge impact basin Odysseus and the long valley Ithaca Chasma. Discovered by Giovanni Cassini, it was imaged by Voyag…
Thalassa — inner moon of Neptune Thalassa (moon) Thalassa (Neptune IV) is a small, irregular inner satellite of Neptune discovered in Voyager 2 images in 1989. It is named for a Greek sea figure and remains little studied beyond…
The Blue Marble (Apollo 17 photograph of Earth) The Blue Marble Iconic full-disk photograph of Earth taken during the Apollo 17 mission in December 1972. Widely reproduced, it shows a fully sunlit globe and has become a symbol of Earth's fragil…
The Star The Star is a widely used name and symbol applied to celestial bodies, a tarot card, newspapers, films, music, brands and more; this article outlines common meanings, examples and…
The Sun: the star at the center of the Solar System The Sun Overview of the Sun: its structure, behavior, history of study, effects on Earth, and future evolution. Covers composition, solar activity, heliosphere, and human uses like energy…
Thebe (moon) Thebe is a small, irregular inner moon of Jupiter, fourth closest to the planet. Discovered in 1979 in Voyager 1 images, it supplies dust to Jupiter's Thebe gossamer ring and is na…
Thelxinoe (Jupiter XLII): a small retrograde moon of Jupiter Thelxinoe (moon) Thelxinoe is a tiny irregular, retrograde satellite of Jupiter discovered from 2003 images and officially catalogued in 2004. It belongs to the Ananke group and orbits at ~20.45 mi…
Themis (hypothetical moon of Saturn) Themis (hypothetical moon) Themis was a claimed 1905 discovery of a tenth Saturnian satellite by William H. Pickering. Later searches failed to verify it, and it is not recognised as an actual moon of Saturn…
Themisto — a small prograde moon of Jupiter Themisto (moon) Themisto is a small prograde irregular moon of Jupiter, first observed in 1975, lost for decades, and rediscovered in 2000. It occupies an isolated orbit between the Galilean satel…
Thrymr (moon) Thrymr is a small, retrograde irregular moon of Saturn discovered in 2000. It orbits far from the planet on a highly inclined, eccentric path and is considered part of the Norse gr…
Thyone (Jupiter XXIX): an irregular, retrograde moon of Jupiter Thyone (moon) Thyone (Jupiter XXIX) is a small, retrograde irregular satellite of Jupiter discovered in 2001. It belongs to the Ananke group and provides insight into capture and collisional pro…
Tidal locking: gravitational synchronization of rotation and orbital motion Tidal locking Overview of tidal locking: how gravitational tides synchronize an object's spin with its orbit, the mechanisms and timescales involved, examples (Moon, Pluto–Charon), and implicati…
Titan (moon of Saturn) Titan (moon) Titan is Saturn's largest moon, notable for a dense nitrogen atmosphere, hydrocarbon lakes, and exploration by the Cassini–Huygens mission. It is larger than Mercury but less massi…
TALISE — Titan Lake In-situ Sampling Propelled Explorer Titan Lake In-situ Sampling Propelled Explorer TALISE is a proposed boat-like probe designed to sail and sample Ligeia Mare on Saturn's moon Titan, making in-situ chemical, physical and environmental measurements of an extrater…
Titania — largest moon of Uranus Titania (moon) Titania is Uranus's largest satellite and the eighth largest moon in the Solar System. It has a heavily cratered, icy surface crossed by large canyons and was imaged by Voyager 2 i…
Trans-Neptunian object A trans-Neptunian object is a minor planet that orbits beyond Neptune. The group includes Kuiper belt objects, scattered-disc bodies, and dwarf planets such as Pluto.
Transit of Venus: rare planetary crossing of the Sun Transit of Venus A transit of Venus occurs when Venus passes directly between Earth and the Sun. These events are rare, last hours, follow a 243-year cycle, and played a key role in measuring the a…
Transiting Exoplanet Survey Satellite (TESS) Transiting Exoplanet Survey Satellite NASA space telescope launched in 2018 to survey bright nearby stars for transiting exoplanets, using wide-field cameras to produce an all-sky catalog of planet candidates for follo…
Triangulum (constellation) Triangulum Triangulum is a small northern constellation named for its triangular shape. It is one of the 88 modern constellations and contains the nearby Triangulum Galaxy (M33).
Triangulum Australe (Southern Triangle) Triangulum Australe Triangulum Australe, the Southern Triangle, is a small southern-hemisphere constellation formed by three bright stars; notable for its triangular shape, bright star Atria, and role…
Triangulum Galaxy (M33) Triangulum galaxy Triangulum (M33) is a nearby spiral galaxy about 3 million light‑years away in the constellation Triangulum; a Local Group member used to study star formation and galaxy structure.
Trifid Nebula (M20): Overview, Structure, and Observing Guide Trifid nebula The Trifid Nebula (M20) is a mixed emission, reflection and dark nebula in Sagittarius about 5,200 light-years away, notable for its three dust lanes, active star formation, and vi…
Triton — Neptune's largest moon Triton (moon) Triton is Neptune's largest moon, notable for its retrograde orbit, icy surface, active geology, tenuous nitrogen atmosphere and likely origin as a captured Kuiper Belt object; stu…
Trojan asteroid Small bodies that share a planet's orbit near the stable L4 and L5 Lagrange regions; best known around Jupiter and studied as remnants of early Solar System formation.
Tucana (constellation) Tucana Tucana is a southern constellation representing the toucan; it contains the Small Magellanic Cloud and the bright globular cluster 47 Tucanae and was introduced by early European e…
TV Geminorum — a large red giant star in Gemini TV Geminorum TV Geminorum is a red giant star in the constellation Gemini notable for its very large radius—hundreds of times that of the Sun—and for the insights it provides into late stellar…
Tyche — hypothetical gas giant proposed in the Solar System's Oort cloud Tyche (planet) Tyche is a proposed, now largely disfavored, gas-giant-sized object in the Solar System's Oort cloud, suggested to explain patterns of long‑period comets; infrared surveys later fo…
Tycho's Supernova (SN 1572): historical sighting and its modern remnant Tycho's Supernova SN 1572, known as Tycho's Supernova or B Cassiopeiae, was a naked-eye Type Ia supernova observed in 1572. Its remnant is an important object for studies of explosion physics, shock…
U Lacertae — a binary star with a red supergiant in Lacerta U Lacertae U Lacertae is a binary star system in the Lacerta constellation whose primary is a red supergiant reported to have a radius roughly 1,022 times that of the Sun. The system is of in…
UDFj-39546284: candidate for one of the earliest observed galaxies UDFj-39546284 UDFj-39546284 is a faint infrared source identified in Hubble deep-field imaging and interpreted as a candidate galaxy from about 380 million years after the Big Bang (photometric,…
Ulysses (spacecraft) Ulysses was a joint NASA–ESA space probe launched in 1990 to study the Sun from high latitudes. It used a Jupiter gravity assist to observe the solar poles and the heliosphere over…
