Astronomy

Kyokko — Japanese artificial satellite launched in 1978 Kyokko Kyokko was a Japanese artificial satellite placed into orbit on 4 February 1978. It was developed by the Institute of Space and Astronautical Science at the University of Tokyo as…

La Silla Observatory — ESO astronomical site in Chile La Silla Observatory La Silla Observatory is a major southern-hemisphere astronomical facility in Chile operated by ESO, hosting many telescopes and instruments that have advanced stellar, planetary an…

Lacerta (constellation) Lacerta Lacerta is a small, faint northern constellation introduced in the 17th century; notable for the BL Lacertae active nucleus and several open clusters amid a rich Milky Way field.

Lagoon Nebula (Messier 8, NGC 6523) — a star-forming emission nebula Lagoon Nebula Messier 8, the Lagoon Nebula (NGC 6523), is a bright H II emission nebula and interstellar cloud in Sagittarius about 4,100 light-years away, known for active star formation and th…

Lagrange point Locations in a two-body orbital system where a small third object can maintain a fixed or quasi-fixed position relative to the pair, used by natural bodies and spacecraft.

Lakes of Titan Hydrocarbon lakes and seas on Saturn’s moon Titan: composition, discovery by Cassini–Huygens, distribution, detection methods, seasonal behavior, scientific importance and future e…

Lalande 21185 — nearby red dwarf in Ursa Major Lalande 21185 Lalande 21185 (Gliese 411) is a nearby M-type red dwarf about 8.31 light‑years away in Ursa Major. It is too faint to see unaided and is frequently studied for its proximity, motio…

Laomedeia (Neptune XII): a small outer moon of Neptune Laomedeia (moon) Laomedeia is a small, irregular satellite of Neptune discovered in 2002. It orbits far from the planet, is likely non-spherical, and is named for one of the Nereids; its diameter i…

Large Zenith Telescope — 6.0‑metre Liquid‑Mirror Observatory Large Zenith Telescope Overview of the Large Zenith Telescope (LZT): a 6.0 m liquid‑mirror zenith telescope near Vancouver, its design, history, uses, advantages and limitations.

Larissa (Neptune moon) Larissa (moon) Larissa (Neptune VII) is an inner satellite of Neptune discovered by ground-based occultation in 1981 and imaged by Voyager 2 in 1989. It is irregular, heavily cratered, and shows…

Las Campanas Observatory High-altitude astronomical observatory in Chile's Atacama, operated by the Carnegie Institution; home to multiple optical telescopes and known for the discovery of Supernova 1987A.

Late Heavy Bombardment — lunar cataclysm and its planetary effects Late Heavy Bombardment Period ~4.1–3.8 billion years ago when many large impacts struck the Moon and other inner planets; evidence, leading theories, and implications for early Earth and Solar System his…

LBV 1806-20: Galactic luminous blue variable candidate and extremely luminous star LBV 1806-20 LBV 1806-20 is an extremely luminous, massive Galactic blue supergiant and LBV candidate—hidden by dust in Sagittarius, observed chiefly in infrared, with radius and luminosity est…

Leda (moon of Jupiter) Leda (moon) Leda is a small, irregular prograde moon of Jupiter and a member of the Himalia group. Discovered in 1974, it is non-spherical and probably a captured or collisional fragment shari…

Lenticular galaxy (S0): intermediate disk galaxies between spirals and ellipticals Lenticular galaxy Lenticular galaxies (S0) are disk systems with a central bulge, little cold gas, and weak star formation; they occupy an intermediate position between spiral and elliptical galaxie…

Leo (astrology) Leo is the fifth zodiac sign, a fixed fire sign ruled by the Sun. Associated with the lion, it represents creativity, leadership and self-expression; in tropical astrology it falls…

Leo (constellation): the Lion of the zodiac Leo (constellation) Leo is a prominent zodiac constellation representing a lion, containing the bright star Regulus and several notable galaxies; visible across the northern hemisphere during late win…

Leo Minor (constellation) Leo Minor Leo Minor is a small, faint constellation in the northern sky, introduced in the 17th century. It lies between Leo and Ursa Major and contains mostly modest stars, a few galaxies a…

Leonids: the November meteor shower from comet Tempel–Tuttle Leonids The Leonids are an annual November meteor shower produced by debris from comet Tempel–Tuttle, notable for fast, bright meteors and occasional storms that peak around November 17 wi…

Lepus (constellation) Lepus is a small southern constellation representing a hare, located just south of Orion. This entry covers its location, main stars, deep-sky objects, history, and how to observe…

Libra (astrology) Libra, the Scales, is the zodiac sign associated with balance, relationships, and aesthetics. It is an air sign ruled by Venus and spans late September to late October in the tropi…

Libra (constellation) Libra is the zodiac constellation of the scales, situated between Virgo and Scorpius. It is modest in brightness but rich in history, symbolism, and several notable stars and deep-…

Lick Observatory — University of California astronomical observatory on Mount Hamilton Lick Observatory Lick Observatory is a historic astronomical facility on Mount Hamilton near San Jose, California, owned by the University of California and managed by the University of California…

Ligeia Mare — a large hydrocarbon sea on Titan Ligeia Mare Ligeia Mare is a vast liquid hydrocarbon sea near Titan's north pole. Mapped by Cassini, it is notable for its size, methane–ethane composition, shoreline channels and interest as…

Light curve (astronomy) Light curve A light curve charts an object's brightness over time. Used to classify variable stars, detect exoplanets, study explosions and lensing, and constrain physical models from periodic…

Light year — the astronomical unit of distance Light year A light year is the distance light travels in a vacuum in one year. It is a unit of length used to express vast astronomical distances and conveys both spatial scale and look-back…

Lincoln Near-Earth Asteroid Research (LINEAR) Lincoln Near-Earth Asteroid Research LINEAR is a U.S. automated sky-survey program, begun in the late 1990s, that discovered tens of thousands of minor planets and many near‑Earth objects using robotic telescopes and…

List of astrophysicists and their roles List of astrophysicists Overview of astrophysicists: roles, career paths, historical development, notable figures and why the field matters, with examples of prominent researchers and typical areas of wor…

List of the Brightest Stars as Seen from Earth List of brightest stars Overview and explanation of the 50 brightest individual stars by apparent magnitude, how apparent magnitude works, distinctions between single stars and multiple systems, and notab…

List of comets: classification, naming, and notable examples List of comets Overview of comet types, naming conventions (P and C prefixes), history, scientific importance, and selected well-known comets with examples and reading tips.

List of craters on Puck Overview and context for the named impact craters on Puck, a small inner moon of Uranus, including naming conventions, observation history, and brief description of their character…

Catalogue and Overview of Exoplanets List of exoplanets Structured guide to lists of exoplanets: how entries are compiled and named, common detection methods, major cataloguing practices, notable discoveries, classifications, and uses a…

Lists and catalogs of galaxies List of galaxies Overview of how astronomers organize and list galaxies: classification, major catalogs and lists, notable examples and groups, and the difference between galaxies and galaxy cluste…

Geological features of Ariel, moon of Uranus List of geological features on Ariel Overview of the named surface structures on Ariel, an icy moon of Uranus: types of features, how they were discovered, naming conventions, and why they matter for planetary geology…

Geological features of Miranda, the Uranian moon List of geological features on Miranda Overview and organization of Miranda's surface features: types (coronae, scarps, grooves, craters), discovery by Voyager 2, naming conventions and importance for planetary geology.

List of Jupiter's moons Comprehensive overview of Jupiter's natural satellites: the major Galilean moons, groups of smaller satellites, orbital characteristics, discovery history, and scientific importanc…

Largest stars by radius: overview and notable candidates List of largest stars Survey of the largest known stars by radius, how sizes are measured, notable red supergiant and hypergiant candidates, and reasons why rankings are uncertain.

List of Most Luminous Stars Overview of the most intrinsically luminous stars known: where they are found, how luminosity is measured, the stellar types involved, and why these rare stars matter in astrophysi…

Nearest galaxies to Earth: list, measurements, and significance List of nearest galaxies Overview and annotated list of galaxies closest to Earth, including Milky Way satellites and nearby Local Group members, with notes on measurement, uncertainty, and scientific impo…

Nearest stars to the Sun: overview and notable nearby systems List of nearest stars Summary of the stars closest to Earth: how distances are measured, the types of nearby objects, prominent examples, scientific importance, and pointers to source catalogs and surve…

List of Neptune's moons Overview and list of Neptune’s 14 known moons, their discovery history, categories (inner, outer, irregular), notable features such as Triton’s retrograde orbit, and naming origins…

List of planets in the Solar System List of planets Overview and classification of Solar System planets: the eight major planets and the commonly recognised dwarf planets, with notes on characteristics, history, and notable distinct…

Types of Telescopes: Optical, Radio, Space and High‑Energy Instruments List of telescope types Survey of telescope families and subtypes, how they collect electromagnetic radiation, technical differences and common scientific uses across visible and non‑visible wavelengths.

Moons of Uranus: names, categories, and a complete list List of Uranus' moons Overview and organized listing of Uranus' 27 known moons, their origins, discovery history, categories, and notable features.

Local Group (galaxy group containing the Milky Way and Andromeda) Local Group The Local Group is the galaxy association that contains the Milky Way, Andromeda and dozens of smaller galaxies. It spans roughly ten million light‑years and is part of the Virgo S…

Lockman Hole (low neutral-hydrogen window in the sky) Lockman Hole A region near Ursa Major with unusually low neutral hydrogen column density. The Lockman Hole provides a comparatively unobstructed line of sight for ultraviolet and X-ray observat…

Loge (Saturn moon) Loge (moon) Loge (Saturn XLVI, S/2006 S 5) is a small, distant irregular moon of Saturn with a retrograde orbit. Discovered in 2006, it belongs to the Norse group and is named after a fire gia…

Longitude of the Ascending Node (Ω) Longitude of the ascending node Angular orbital element giving the angle from a chosen reference direction to the ascending node; specifies orientation of an orbit's line of nodes in a reference plane.