Low Earth orbit (LEO): characteristics, uses, and history Low Earth orbit Low Earth orbit (LEO) is the region of space close to Earth where many satellites, the ISS, and scientific platforms operate. This article summarizes its definition, mechanics, app…
Luhman 16 — nearby binary brown dwarf system Luhman 16 Luhman 16 (WISE 1049−5319) is a nearby binary brown dwarf system about 6.6 light-years away in Vela. It contains two substellar objects near the L/T spectral transition and shows n…
Luminosity (astronomy): intrinsic energy output of stars and objects Luminosity Luminosity is the total electromagnetic power emitted by an astronomical object. This article explains definitions, units, measurement methods, magnitude systems, examples, and obs…
Luminous blue variable (LBV) Luminous blue variable Luminous blue variables are rare, very massive evolved stars that show irregular, sometimes dramatic changes in brightness and spectrum, including S Doradus-type outbursts and occa…
Luna (the Moon): natural satellite, goddess, and cultural symbol Luna Luna is the Latin name for Earth's Moon, a nearby natural satellite noted for its geology, phases, exploration history and cultural significance; also the Roman moon goddess and a…
Luna 1 — Soviet first probe to reach the Moon's vicinity and enter solar orbit Luna 1 Luna 1 (Mechta) was the Soviet Union's first Luna programme probe. Launched in 1959, it passed near the Moon, entered heliocentric orbit and made early measurements of the space en…
Lunar calendar A calendar system that counts months by the Moon's phases. Includes purely lunar systems (e.g., Islamic) and lunisolar variants that add months to keep seasons aligned.
Lunar eclipse A lunar eclipse occurs when Earth's shadow falls on the Moon during a full moon. This article explains the geometry, types, why the Moon reddens, observing tips, and cultural and s…
Lunar mare (maria): the dark basaltic plains of the Moon Lunar mare Dark, basaltic plains on the Moon formed by ancient volcanic eruptions. Often called 'seas', maria cover much of the near side and were important in lunar exploration and mapping.
Lunar south pole: permanently shadowed craters and polar ice Lunar south pole The Moon's south pole hosts deep, permanently shadowed craters that trap water and other volatiles. It is a priority for science and exploration because of ice deposits, unique ill…
Lunisolar calendar A calendar system that reconciles lunar months with the solar year by inserting extra months as needed; used historically and today for religious, agricultural, and civil purposes.
Lunokhod 1 — Soviet lunar rover and first successful remote rover on the Moon Lunokhod 1 Lunokhod 1 was the Soviet Union's remote-controlled lunar rover that landed in 1970. This article covers its design, mission, instruments, operations, scientific contributions and…
Lupus — the southern constellation of the Wolf Lupus (constellation) Lupus is a southern-hemisphere constellation, historically depicted as a wild animal. It lies between Centaurus and Scorpius and contains several bright stars and deep-sky objects…
Luyten 726-8 (Gliese 65): a Nearby flaring red-dwarf binary Luyten 726-8 Luyten 726-8 (Gliese 65, UV Ceti / BL Ceti) is a nearby binary of active M-type red dwarfs about 8.7 light‑years away, notable as the prototype flare star system and for its rapid…
Lynx (constellation) Lynx is a faint northern constellation introduced by Johannes Hevelius. It is known for dim stars, a few interesting deep-sky objects, and its name reflecting the need for keen eye…
Lyra (constellation) Lyra Lyra is a small northern constellation notable for the bright star Vega, the Ring Nebula (M57), the double star Epsilon Lyrae and the prototype variable RR Lyrae.
Lysithea — a small prograde moon of Jupiter Lysithea (moon) Lysithea is a small, irregular prograde moon of Jupiter discovered in 1938. It belongs to the Himalia group and has an elongated shape, a dark surface, and an orbit influenced by s…
M43 (NGC 1982) — De Mairan's Nebula in Orion M43 M43 (NGC 1982), also called De Mairan's Nebula, is an H II emission region adjacent to the Orion Nebula, about 1,600 light-years away and ionized by the star NU Orionis.
M78 (Messier 78) — a reflection nebula in Orion M78 M78 is a bright reflection nebula in the constellation Orion, about 1,600 light-years away. Part of the Orion molecular cloud complex, it is known for its blue appearance and assoc…
Mab (moon of Uranus) Mab (moon) Mab is a small inner satellite of Uranus, discovered in 2003 with the Hubble Space Telescope. Its dark, uncertain surface and perturbed orbit link it to Uranus's faint dusty rings…
Magellan (spacecraft) — Venus Radar Mapper Magellan (spacecraft) Magellan was a NASA mission that orbited Venus (1990–1994) using radar to produce near-global surface maps and gravity data, revealing volcanic and tectonic features beneath the cl…
Magellan Telescopes A pair of 6.5‑metre optical telescopes at Las Campanas Observatory in Chile, operated by a U.S. consortium and used for imaging, spectroscopy, adaptive optics and exoplanet researc…
Magellanic Clouds Two irregular dwarf companion galaxies of the Milky Way, visible mainly from the southern hemisphere and important for studies of star formation and galactic interaction.
Magnetar A magnetar is an unusual, highly magnetized neutron star whose decaying magnetic field powers persistent X-ray emission, short bursts and occasional giant flares.
Magnetosphere (planetary magnetic environment) Magnetosphere Region around a planet or star where magnetic fields steer charged particles, shaping space weather, auroras, and boundaries like the magnetopause and magnetotail.
Astronomical magnitude — measuring the brightness of celestial objects Magnitude (astronomy) Scale and concepts behind astronomical magnitude: how brightness is measured, common values, photometric bands, historical origin, and distinctions like apparent vs absolute magnit…
Main sequence (stellar evolution and observational significance) Main sequence The main sequence is the long-lived band of hydrogen-fusing stars on the Hertzsprung–Russell diagram, spanning hot, massive O-types to cool, low-mass M-types and defining stellar l…
Makemake: A Trans-Neptunian Dwarf Planet in the Outer Solar System Makemake (dwarf planet) Makemake is a distant dwarf planet in the Kuiper belt, discovered in 2005. This article summarizes its discovery, composition, orbit, known moon, and scientific significance.
Mare Tranquillitatis — the Sea of Tranquility Mare Tranquillitatis Mare Tranquillitatis is a dark, basaltic plain on the Moon's near side, famed as the Apollo 11 landing site. It formed from ancient lava flows and is a prominent lunar mare studied…
Margaret (Uranus moon) Margaret (moon) Margaret is the only known prograde irregular moon of Uranus. Discovered in 2003, it orbits far from the planet on an inclined, eccentric path and is named for a character in Shake…
Mariner 1: NASA’s First Mariner Mission and Its Early Failure Mariner 1 Mariner 1 was the United States' first spacecraft in the Mariner series, intended for a Venus flyby in 1962; it was destroyed shortly after launch after the booster veered off cour…
Mariner 10: NASA's First Mission to Mercury Mariner 10 Mariner 10 was a NASA robotic probe launched in 1973 that performed flybys of Venus and Mercury, returning the first close-up images and many of the first scientific measurements o…
Mariner 2: NASA’s First Successful Planetary Flyby Mariner 2 Mariner 2 was NASA’s first spacecraft to successfully fly past another planet (Venus) in 1962. Its observations established Venus as extremely hot and provided early measurements o…
Mariner 3 - NASA's early Mars probe and its mission failure Mariner 3 Mariner 3 was a 1964 NASA planetary probe intended to image Mars and study interplanetary space. A protective shroud failed to separate, the spacecraft lost power and entered helio…
Mariner 4: NASA's First Successful Mars Flyby and Close-Up Images Mariner 4 Mariner 4 was the first spacecraft to return close-up photographs of Mars and to probe its atmosphere, reshaping knowledge of the planet with a brief eight-month flyby mission laun…
Mariner 9 — NASA's first Mars orbiter Mariner 9 Mariner 9, launched in 1971, was the first spacecraft to orbit another planet. It mapped much of Mars, revealed Valles Marineris and large volcanoes, and studied atmospheric and su…
Mariner program: NASA's early planetary exploration missions Mariner program U.S. NASA robotic program that sent ten Mariner spacecraft in the 1960s–1970s to study Venus, Mars and Mercury, achieving first flybys, the first planetary orbiter, and pioneering…
Mars: Overview, Characteristics, and Exploration Mars Mars is the fourth planet from the Sun, a cold, rocky terrestrial world with polar ice, a thin CO2 atmosphere, large volcanoes and canyons, two small moons, and a long history of r…
Mars Climate Orbiter — NASA mission and unit‑conversion failure Mars Climate Orbiter NASA's Mars Climate Orbiter (launched 11 Dec 1998) was designed to study Martian weather and relay data. It was lost during Mars orbit insertion on 23 Sep 1999 after a units conver…
Mars flyby A Mars flyby is a spacecraft close pass of Mars that gathers scientific and engineering data without entering orbit or landing; used by robotic probes for reconnaissance, instrumen…
Mars in fiction: themes, history, and notable works Mars in fiction Survey of how Mars has been imagined in literature and other media: origins of canal myths, major themes (invasion, dying world, colonization), and representative works and influen…
Mars Orbiter Mission (Mangalyaan) Mars Orbiter Mission India's first interplanetary probe, launched by ISRO in 2013 and placed in Mars orbit in 2014. Mangalyaan demonstrated affordable deep-space capability and delivered imaging and at…
Mars Orbiter Mission 2 (Mangalyaan 2) Mars Orbiter Mission 2 ISRO's follow-up Mars orbiter project, Mangalyaan 2, is a planned Indian spacecraft intended to study Mars from orbit after the success of the first Mangalyaan mission.
Mars Reconnaissance Orbiter NASA orbiter launched in 2005 and at Mars since 2006; maps surface and atmosphere, probes subsurface ice, and serves as a high-capacity communications relay for landers and rovers.
Mars Science Laboratory (MSL) — the Curiosity rover mission Mars Science Laboratory NASA's Mars Science Laboratory delivered the Curiosity rover to Gale Crater in 2012 to assess past habitability, study geology and climate, and perform long‑duration in situ chemic…
Mean anomaly (orbital element) Mean anomaly The mean anomaly is a time-linear angular parameter in orbital mechanics used to relate a body's time since periapsis to a position angle via Kepler's equation.
Megaclite — a small retrograde irregular moon of Jupiter Megaclite (moon) Megaclite is a small, retrograde irregular moon of Jupiter discovered in 2000. Part of the Pasiphaë group, it orbits at ~24.7 million km with a period of ~792 days and is about 5.4…
Melbourne Observatory 19th‑century observatory in Melbourne’s Royal Botanic Gardens, noted for timekeeping, meteorology and the 48‑inch Great Melbourne Telescope; now a heritage precinct with public pro…
