An Etymological Dictionary of Astronomy and Astrophysics

A shiny silicate mineral composed of varying amounts of → aluminum, → potassium, → magnesium, and → iron. Mica appears as thin, flexible layers in → granite and other rocks, or as → crystals. It is used as a thermal or electrical → insulator.

See also: From L. mica “crumb, grain.”

An apparatus that produces interference fringes by splitting a beam of monochromatic light so that one beam strikes a fixed mirror and the other a movable mirror. When the reflected beams are brought back together, an interference pattern results. It is used to measure very precise lengths, such as the wavelength of light, and for high-resolution spectroscopy.

Etymology (EN): Named after Albert Abraham Michelson (1852-1931), German-American physicist, who built the interferometer for the → Michelson-Morley experiment of 1887; → interferometer.

Etymology (PE): Andarzanešsanj, → interferometer.

An experiment performed in 1887 to establish the presence or absence of an → ether, a medium through which light was supposed to travel. The experiment aimed to measure the speed of light coming from different directions. However no → ether drift was found. The null results obtained showed that the ether hypothesis was incorrect.
Consequently, the theory of → special relativity, with its hypothesis that the speed of light is the same in all → inertial frames, reconciled the results of the Michelson-Morley experiment with the rest of physics.

See also: → Michelson interferometer; Michelson received the Nobel Prize in 1907 for his work, the first American to receive the Prize in science. Edward Williams Morley (1838-1923), an American chemist; → experiment.

Same as → apogee full Moon.

See also: → micro-; → Moon.

1. A combining form for “small.”
   
2. A prefix meaning one millionth (10^-6).

Etymology (EN): From Gk. mikros “small.”

Etymology (PE): Riz-, from riz “very small.”

The area of computer science dealing with the use and development of microcomputers, and related peripheral devices and softwares. Also microinformatics.

Etymology (EN): → micro-; → compute.

Etymology (PE): Riz-, → micro-; azdâyik, → informatics.

Anything that is regarded as a world in miniature.
A unity that is an epitome of a larger unity; opposed to macrocosm.

See also: → micro-; → cosmos.

The state or condition where the force of → gravity is very weak, e.g. the → weightlessness experienced inside an orbiting spacecraft.

See also: → micro-; → gravity.

A type of → gravitational lens, where the foreground
→ lensing object is of low mass, and the multiple images produced are too close together on the sky to be observed as separate images.

Gravitational microlensing occurs when a foreground star happens to lie very close to our line of sight to a more distant background star. The foreground star acts as a lens, splitting the light from the background source star into two or more images, which are typically unresolved. However, these images of the source are magnified, by an amount that depends on the angular separation between the lens and source. If with the passage of time the lens moves across the Earth-source, the amount of brightening changes. Typically the source will appear to brighten, reach a maximum and then fade symmetrically back to normal over the course of a few weeks or months; this is called a → microlensing event. If the foreground star happens to host a planet with projected separation near the paths of these images, the planet will also act as a lens, further perturbing the images and resulting in a characteristic, short-lived signature of the planet.

Microlensing is used in the search for → dark matter in the → Milky Way galaxy and its nearest neighbours, as well as for → extrasolar planets

(e.g. B. S. Gaudi, 2010, arXiv:1002.0332).

See also: → micro-; → lensing.

Determining the three various parameters of a microlensing event
(the lens-source relative parallax and proper motion, and the mass of the lens)
from only one physical parameter (the event time scale). Currently
the microlensing degeneracy affects the vast majority of events and
makes any individual event impossible to interpret with certainty.

See also: → microlensing; → degeneracy.

The effect arising whenever a source star and lens star pass each other at an angular separation involving the → Einstein radius (R_E) of the lens. The time-scale for such an event is defined as t_E = R_E/v, where v is the magnitude of the relative transverse velocity between source and lens projected onto the lens plane.

See also: → microlensing; → event.

A small grain sized meteorite which can only be positively identified under the microscope.

See also: → micro-; → meteorite.

1. A screw thread device used to make accurate physical linear measurements.
   
2. Same as → micron.

See also: → micro-; → -meter.

A unit of length in the → metric system equal to one millionth of a → meter (10^-6 m); symbol μm. Also called → micrometer. The average thickness of a human hair is about 50 μm (30-100 μm). The human eye cannot see anything smaller than 40 μm in size. Other small sizes: white blood cells = 15 μm; red blood cells = 8 μm; bacteria 2 μm.

See also: Coined 1880 in Fr. from Gk. mikron, neutral of mikros “small.”

A localized → thermonuclear burst on the surface layers of an → accreting white dwarf. In comparison, classical → nova explosions are caused by global → thermonuclear runaways on the surface of such white dwarfs.

Micronovae are less powerful than novae; they have been observed to release up to 10³⁹ ergs of energy, that is approximately 10⁶ times less than the energies released in classical novae (thus the term micronova describing these events). They are also much short-lived, lasting only several hours, while nova outbursts last for weeks.

The micronova phenomenon is provoked by the accumulation of accreted matter on the poles of → white dwarfs under the confining effect of strong → magnetic fields (S. Scaringi et al., 2022, arXiv:2204.09073).

See also: → micro-; → nova.

Any organism too small to be seen by the naked eye, e.g. bacteria, viruses, and protozoa.

See also: → micro-; → organism.

Controlling unit of a microcomputer; laid out on a tiny silicon chip and containing the logical elements for handling data, performing calculations, carrying out stored instructions, etc.

See also: → micro-; → processor.

A → binary system where an ordinary star orbits around a → neutron star or a → stellar-mass black hole
that accretes the outer layers of the star’s atmosphere.
The accreted material falling on the → compact object warms up drastically and emits huge amounts of energy as → X-rays. The → accretion disk that emits this radiation also produces → relativistic jets of → plasma along the rotation axis of the compact object. The jets of material exhibit superluminal motion and resemble those emitted from → quasars, but on scales millions of times smaller. The first microquasar, 1E1740.7-2942, was discovered by F. Mirabel et al. 1992, Nature, 358, 215.

See also: → micro- + → quasar.

A magnifying optical instrument for inspecting objects too small to be seen or too small to be seen distinctly and in detail by the unaided eye.

Etymology (EN): From Mod.L. microscopium “an instrument for viewing what is small,” from Gk. → micro- + -skopion “means of viewing,” from skopein “look at.”

Etymology (PE): Rizbin, from riz→ micro- + bin “to see; seer” (present stem of didan;
Mid.Pers. wyn-; O.Pers. vain- “to see;” Av. vaēn- “to see;”
Skt. veda “I know;” Gk. oida “I know,” idein “to see;” L. videre “to see;” PIE base *weid- “to know, to see”).

Being or characterized as exceedingly small; not large enough to be seen with the naked eye. Compare → macroscopic. → macroscopic state.

See also: → microscope; → -ic.

Same as → microstate.

See also: → microscopic; → state.

The Microscope. A minor constellation in autumn southern sky lying just south of → Capricornus at 21h right ascension, 37° south declination.
The constellation contains only 4th magnitude or fainter stars. Abbreviation: Mic; genitive: Microscopii.

See also: Microscopium was named by Abbé Nicolas Louis de Lacaille (1713-1762); → microscope.

Statistical physics: For a system made up of a large number of components, a state of the system which is specified by describing the current dynamical variables of each constituting component. For example, for a gas system composed of a large number of molecules, the microstate is defined by the set of quantities which defines the state of each molecule in the system (position, velocity, vibration, etc.). In practice, it is impossible to know perfectly the microstate of a system. The aim of → statistical physics is to relate the macroscopic (average ) observables (→ pressure, → temperature, → internal energy) to the microstate of the system. Also called → microscopic state. See also → macrostate and → multiplicity.

See also: → micro-; → state.

The → turbulence phenomenon involving relatively smaller physical volumes compared to → macroturbulence.
In stellar atmospheres, it is a bulk gas motion with a characteristic size less than the local photon → mean free path. Microturbulence is one of the most significant mechanisms that can cause → line broadening in the stellar spectrum. The presence of microturbulence de-saturates strong lines and increases their → equivalent widths. Microturbulence in → hot stars brings about gas motions with velocities 0-20 km s^-1. A physical connection may exist between microturbulence in hot star atmospheres and a subsurface → iron convection zone. Microturbulence may also be at the origin of → wind clumping in hot stars.

See also: → micro-; → turbulence.

Electromagnetic radiation having wavelengths in the 1 to 300 mm range.

See also: → micro-; → wave.

Thermal radiation with a temperature of 2.73 K that is apparently uniformly distributed in the Universe. It is believed to be a redshifted remnant of the hot radiation that was in thermal equilibrium with matter during the first hundred thousand years after the Big Bang. Same as → cosmic microwave background (CMB) radiation.

See also: → microwave; → background;
→ radiation.

A type of electrically operated oven that cooks food very quickly using microwaves instead of heat.

See also: → microwave; → oven.

Electromagnetic radiation carried by → microwaves.

See also: → microwave; → radiation.

A prefix which means being at or near the middle point of; being or occupying a middle place or position.

Etymology (EN): M.E., from O.E. midd-,
cognate with O.H.G. mitti, O.N. mithr,
Gothic midjis, O.Ir. mide, L. medius,
Gk. mesos, Skt. mádhya-, Av. maidiia- “middle, the middle,” Pers. miyân, as below.

Etymology (PE): Miyâni, from miyân “within, between, center,” from Mid.Pers. mayân “middle; among, between,” Av. maidiia- “middle, the middle,” maiδiiāna- “middle, center,” maδəma- [adj.] “middle, being in the middle; middling, of a middling size or quality,” maiδim “in the midst of,” cf. Skt. mádhya- “middle, located in the middle;” O.H.G. mitti “located in the middle.”
nim-, nimé, → half.

An immense chain of underwater mountains that runs down the middle of the Atlantic Ocean. The MAR, approximately 500-1000 km wide, extends 16,000 km from Iceland to the Antarctic Circle. The MAR is so high that it actually rises above sea level in many places, forming volcanic islands. The Azores, Ascension, St. Helena, and Iceland all arise from this great Atlantic range.
The chain results from the movement of the continental plates. As these plates slowly separate, they leave gaps in the → Earth’s crust. This allows molten rock from beneath the Earth’s crust to reach the surface and forms a ridge. The MAR is a part of the global → mid-ocean ridge system.

See also: → mid-; → Atlantic; → ridge.

The portion of the → electromagnetic radiation lying between the → near-infrared and the → far-infrared. This covers the wavelength range approximately from 8 to 30 → microns.

See also: → infrared radiation, → submillimeter radiation.

See also: → mid-; → infrared.

Any of submarine mountain ranges that stretch around the world through the Atlantic Ocean and across the Pacific and Indian Oceans.
Such ridges generally stand about 1000 m to 3000 m above the adjacent ocean floor and are about 500-1000 km in width.

See also: → mid-; → ocean; → ridge.

The middle of the day; noon or the time centering around noon.

See also: → mid-; → day.

The point, part, position, etc., equidistant from extremes or limits.

Etymology (EN): M.E., O.E. middel; cf. M.L.G., Du. middel, Ger. mittel, variant mid; cognate with Pers. miyân, as below; from PIE *medhyo-.

Etymology (PE): 1) Miyân “within, between, center,” from Mid.Pers. mayân “middle; among, between,” Av. maidiia- “middle, the middle,” maiδiiāna- “middle, center,” maδəma- [adj.] “middle, being in the middle; middling, of a middling size or quality,” maiδim “in the midst of,” cf. Skt. mádhya- “middle, located in the middle;” O.H.G. mitti “located in the middle.”
2) From miyân + suffix -i.

The region lying between the → troposphere and the → thermosphere comprising the → stratosphere and the → mesosphere (Meteorology Glossary, American Meteorological Society).

See also: → middle; → atmosphere.

Same as → mid-infrared.

See also: → middle; → infrared.

The latitude belt roughly between 35 and 65 degrees North and South. Also referred to as the temperate region.

See also: → middle; → latitude.

Logic: In a → syllogism, the categorical term occurring in both the → major term and the → minor term.

See also: → middle; → term.

Generally, the middle of the night as indicated by twelve o’clock at night.
True midnight: The time when the Sun is closest to nadir and the night is equi-distant from dusk and dawn. The opposite of noon.

Etymology (EN): From mid- an E. combining form related to → middle; → night.

Etymology (PE): Nimšab, from nim “mid-, half” (Mid.Pers. nêm, nêmag “half;” Av. naēma- “half;” cf. Skt. néma- “half”) + šab, → night

The phenomenon occurring when the Sun is visible above the horizon at midnight.
This phenomenon can be seen at positions north of the Arctic Circle and south of the Antarctic Circle when the Sun is circumpolar (around the summer solstice in the northern hemisphere and the winter solstice in the southern hemisphere respectively).

See also: → midnight, → sun.

The scattering of → electromagnetic waves by → particles of → size comparable to the radiation → wavelength. Mie scattering depends weakly upon the wavelength, hence the → scattered light spectrum is similar to that of the → incident light. Mie scattering explains the → white color of clouds when scattering is due to → water droplets having a size of few microns. Cloud → droplets with a diameter of around 20 microns or so are large enough to scatter all visible wavelengths more or less equally. Because all wavelengths are scattered, clouds appear to be white.

When clouds become very deep, less and less of the incoming solar radiation makes it through to the bottom of the cloud, which gives these clouds a darker appearance.

See also: Named after Gustav Adolf Mie (1868-1957), a German physicist, whose theory of 1908 explains the process; → scattering.

The explanation of the → scattering of → electromagnetic waves by → homogeneous spheres of arbitrary → size and → composition using analytical solutions of → Maxwell’s equations. See also: → Mie scattering, → Rayleigh scattering.

See also: → Mie scattering; → theory.

1. To go from one country, region, or place to another.
   

2. To pass periodically from one region or climate to another, as certain birds, fishes, and animals.
   

3. Chem.: To move toward an electrode during electrolysis; (of atoms within a molecule) to change position (Dictionary.com).

Etymology (EN): From L. migratus p.p. of migrare “to move from one place to another,” ultimately from PIE *meig^h- “to move, go;” cf. Gk. ameibein “to change,” Iranian muž-, as below.

Etymology (PE): Mužidan, ultimately from Proto-Ir. *maij- “to move (to places);” cf. Parachi muž-, muš-, Yazghulami mûž- “to go,” mex^w-/max^wt- “to move, shake,” Gilaki maxtan “to stroll,” Gonâbâdi mejon “ague, shivering, shaking chills,” Sangesari moj; cognate with L. migrare “to move, go,” as below, Skt. niméghanāna- “moving down;” PIE *meig^h- “to move, go.”

1. The process or act of migrating; a migratory movement.
   

2. For an astronomical body, the process or act of changing its place over considerably large distances under the effect of certain physical forces. See, for example, → orbital migration; → Type I migration; → Type II migration.
   

3. Chem.: A movement or change of position of atoms within a molecule (Dictionary.com).

See also: → migrate; → -tion. Kuc “the act of moving from a dwelling, a place to another, decamping, migration.”

Migrating; periodically migrating; pertaining to migration.

See also: → migrate + -ory, an adj.-forming suffix.

A → NASA funded project to support and provide to the astronomical community a variety of astronomical data archives, with the primary focus on scientifically related data sets in the optical, ultraviolet, and near-infrared parts of the spectrum. MAST is a huge database that contains astronomical observations of stars, planets and galaxies from 16 separate NASA space science missions, including the Hubble Space Telescope. It is located at the Space Telescope Science Institute (STScI).

See also: In honor of senator Barbara A. Mikulski for her active support for science, NASA, and the astrophysics community; → archive; → space; → telescope.

The theory according to which variations in the elements of Earth-Sun geometry are responsible for the sequence of ice ages during the Pleistocene era. The main elements are the varying tilt of the Earth’s rotational axis, and the varying eccentricity of the Earth’s orbit.

Etymology (EN): Named after the Serbian mathematician Milutin Milankovitch (1879-1958), who introduced the concept during the first half of the twentieth century.

An opaque white fluid secreted by female mammals for the nourishment of their young.

Etymology (EN): M.E.; O.E. meol(o)c, (Anglian) milc; cf. Gr. Milch, Goth. miluks; akin to L. mulgere, Gk amelgein “to milk;” PIE base *melg- “wiping, stroking;”

Etymology (PE): Šir “milk;” Mid.Pers. šir; (Parth. šyft); Khotanese švida; Sogd. xšiβd (Yaghnobi xšift; Yadgha xšira); Av. xšvid-, xšvipta-; cf. Skt. ksira- “milk.”

The diffuse glowing band of light seen on dark nights spanning the sky as a great circle. It is produced by light from stars and nebulae in the → Galactic plane. The apparent form of the Milky Way in the sky results from a geometrical effect created by our location in the outlying regions of a huge, flattened disk of stars. → Milky Way galaxy.

Etymology (EN): From L.L. galaxias “Milky Way,” from Gk. galaxis kyklos “emilky circle,” from gala (gen. galaktos) “milk.”

In Gk. mythology, Jupiter, hoping to immortalize his infant son Hercules (who was born to a mortal woman), placed the baby on Juno’s breast. Her milk spilled up, forming the Milky Way.
Milky, from milk; M.E.; O.E. meol(o)c, (Anglian) milc; cf. Gr. Milch, Goth. miluks; akin to L. mulgere, Gk amelgein “to milk;” PIE base *melg- “wiping, stroking;” → way.

Etymology (PE): Râh, → way; širi, adj. of šir “milk;” Mid.Pers. šir; cf. Skt. ksira- “milk.”

A → spiral galaxy, of which the → solar system is a small part. It is the second largest in our → Local Group of galaxies. The Milky Way is a disk-shaped system, with a diameter of between 80,000 and 100,000 → light-years and a thickness of about 2,000 light-years, containing more than
10¹¹ stars. The stars are divided into two main categories, → Population II stars and → Population I stars.

The core, or nucleus, of the Galaxy is surrounded by an ellipsoidal central → bulge
that measures some 15,000 light-years in diameter and about 6,000 light-years in the direction perpendicular to the plane of the disk. Surrounding the bulge and extending in a near spherical distribution above and below the → Galactic plane is the → Galactic halo. The halo contains about 200 → globular clusters and an extremely thinly scattered population of individual stars.

The Sun is located just over half way out from the center to the edge of the disk at a distance of about 25,000 light-years. In common with other stars, the Sun revolves around the → Galactic Center. Its → orbital velocity is about 220 km s^-1 and its → orbital period is about 225 million years. Overall, the Galaxy exhibits → differential rotation, that is stars and gas clouds closer to the center have shorter orbital periods than those that are located further out.

The → spiral arms of the Milky Way lie
within its disk, where bright → young stars, → H II regions, and → molecular clouds of gas and dust are concentrated into curved “arms” that appear to radiate from the central bulge in a spiral pattern. The Galaxy’s spiral pattern consists of several major arms and a number of shorter segments, one of which, the → Orion arm, contains the Sun and the Orion star-forming region.

Near-infrared observations have shown that the stars in the central bulge are arranged in an elongated → galactic bar, about twice as long as it is wide, that is seen nearly end on from the present location of the solar system. The exact center, or nucleus, of the Galaxy coincides with a strong source of radio emission, called → Sagittarius A, that is less than 15 astronomical units in diameter. Observations of the speeds at which clouds of ionized gas are revolving round the → Galactic center imply that several million solar masses of material are concentrated within a region of about one light-year in radius. Since only about half of this mass can be accounted for by stars, it seems likely that the balance (about 2.5 million solar masses) is contained in a central black hole and that accretion onto this black hole is the underlying source of the energy radiated by Sagittarius A.

The Milky Way also has a → dark matter component. The Galactic → rotation curve indicates that there is a large amount of invisible → non-baryonic surrounding the whole Galaxy.

See also: → Milky Way; → galaxy.

The huge star system of which the Sun is a member. Same as the Galaxy or the Milky Way galaxy.

See also: → Milky Way; → system.

A chemical experiment conducted in 1953 that aimed at checking Alexander Oparin’s and J. B. S. Haldane’s hypothesis that under putative conditions present in the atmosphere of the early Earth inorganic molecules would spontaneously form organic molecules. Miller and Urey filled a sterile flask with a mixture of water, ammonia, methane, and hydrogen. The mixture was heated to evaporate water to produce water vapor. High-voltage electric sparks were passed through the mixture to simulate lightning. After a week, contents were analyzed. Amino acids, the building blocks for proteins, were found.

See also: Named after Stanley L. Miller (1930-2007) and Harold C. Urey (1893-1981); → experiment.

Prefix meaning one thousandth (10^-3).

Etymology (EN): From Fr., from L. mille “thiusand.”

Etymology (PE): Mili-, loan from Fr.

A unit of angle equal to one thousandth of an → arcsecond, or 1/3 600 000 degree.

See also: → milli-; → arcsecond.

One thousandth of a bar; a unit of atmospheric pressure. The average atmospheric pressure at sea level is 1.01325 bars or 1013.25 mb.

See also: → milli-; → bar.

A precision experiment for measuring the → electron charge. By studying the falling speed of small charged droplets in the gravitational field of the Earth subjected to an adjustable electric field, Millikan (1909) was able to demonstrate conclusively the discrete nature of electric charge, and moreover measure the charge of an individual electron.

See also: Robert Andrews Millikan (1868-1953); → experiment.

Microwaves with wavelengths between 1 and 10 millimeter, corresponding to frequencies between 300 GHz to 30 GHz. → millimeter-wave astronomy.

See also: → milli-; → meter; → wave.

That part of radio astronomy which uses electromagnetic waves in the range 1-10 millimeter to study various components of the Universe, in particular the chemistry of interstellar matter.

See also: → millimeter wave; → astronomy.

A thousand thousand (10⁶).

Etymology (EN): O.Fr. million, from It. millione, literally “a great thousand,” augmentative of mille “thousand,” from L. mille.

Etymology (PE): Milyon, Loan from Fr.

A type of pulsar that spins around its axis every few thousands of a second. The prototype 1937+21, discovered in 1982, has a period of 1.56 milliseconds; i.e. it spins more than 600 times per second, the fastest so far found (Backer et al. 1982, Nature 300, 615). These pulsars are distinguished from typical pulsars by the extreme stability of their rotation period. It is thought that they have been rejuvenated by a “spin-up process” involving the accumulation of matter from a companion star. → recycled pulsar.

See also: → milli-; → second; → pulsar.

One thousands of a → sievert.

See also: → milli- + → sievert.

A design of → radio interferometer made of two lines of → antennae at right angles to one another.

See also: Named after the Australian engineer and astronomer Bernard Yarnton Mills (1920-2011; see R.H. Frater et al. 2013, arXiv:1306.6371); → cross.

Same as → Milne Universe.

See also: → Milne Universe; → cosmological; → model.

A model of the → Universe which is devoid of matter and where the → space-time is → open
(Ω_M = 0, Ω_R = 0, Ω_Λ = 0, k = -1). The Universe will expand at a constant rate for ever. See also → empty Universe, → de Sitter Universe.

See also: Put forward by Edward Arthur Milne (1896-1950), a British astrophysicist, who introduced the → cosmological principle; → cosmological; → model.

The approximation of a stellar atmosphere with a plane parallel grey atmosphere in radiative equilibrium. It is assumed that a spectral is formed in such a way that the ratio of the line absorption coefficient to the continuous absorption coefficient is constant with depth.

See also: → Milne Universe; Arthur Stanley Eddington (1882-1944), prominent British astrophysicist; → approximation.

The seventh of Saturn’s known satellites. It is 392 km in diameter and orbits Saturn at a mean distance of 185,520 km. Mimas’ low density (1.17) indicates that it is composed mostly of water ice with only a small amount of rock. The surface is saturated with impact craters, dominated by the largest one measuring 130 km across, known as Herschel. Mimas was discovered in 1789 by Herschel.

See also: In Gk. mythology, Mimas was one of the Gigantes slain by Hephaestus, the god of fire, volcanism, smiths and craftsmen, with barrage of red-hot metal.

1. The human faculty to which are ascribed thought, feeling, etc; often regarded as an immaterial part of a person (Dictionary.com).
   

2. Psychology: The totality of conscious and unconscious → mental processes and activities (Dictionary.com).

Etymology (EN): M.E. mynd(e), from O.E. gemynd “memory, remembrance; thought, purpose” (cf. Gothic muns “thought,” munan “to think;” ON minni “mind;” Ger. Minne (archaic) “love,” originally “memory”), from PIE root *men- “think, remember;” cf. Pers. mân, man “mind, thought;” Av. man- “to think;” Skt. matih “thought,” Gk. mania “madness,”
mentio “remembrance;” Lith. mintis “thought, idea,” O.C.S. mineti “to believe, think,” Russ. pamjat “memory.”

Etymology (PE): Ment, from Mid.Pers. mênitan “to think,” Av. mainyeite “he thinks;” O.Pers. man- “to think,” maniyaiy “I think,” Ardumaniš- (proper noun) “upright-minded,” Haxāmaniš- (proper noun, Hellenized Achaemenes, founder of the Achaemenian dynasty) “having the mind of a friend;” Av. mân- “to think,”
manah- “mind, thinking, thought; purpose, intention,” mainyu- “mind, mentality, mental force, inspiration,” cf. Sogdian mân “mind;” Skt. man- “to think,” mánye “I think,” manyate “he thinks,” mánas- “intelligence, understanding, conscience;” Gk. mainomai “to be angry,” mania “madness,” mantis “one who divines, prophet;” L. mens “mind, understanding, reason,” memini “I remember,” mentio “remembrance;” Lith. mintis “thought, idea;” Goth. muns “thought,” munan “to think;” Ger. Minne “love,”
originally “loving memory;” O.E. gemynd “memory, thinking, intention;” PIE base
*men- “to think, mind; spiritual activity.”

A naturally occurring inorganic solid. The internal crystalline structure of a mineral is controlled by its elemental composition.

Etymology (EN): From M.L. minerale “something mined,” from neuter of mineralis “pertaining to mines,” from minera “mine.”

Etymology (PE): Kâni “mineral,” from kân “mine,” from kandan “to dig” (Mid.Pers. kandan “to dig;” O.Pers. kan- “to dig,” akaniya- “it was dug;” Av. kan- “to dig,” uskən- “to dig out” (→ ex- for prefix us-); cf. Skt. khan- “to dig,” khanati “he digs”).

A black hole of mass as low as 10^-6 gram supposed to have formed in the early Universe following the Big Bang event.
Same as primordial black hole.

See also: Mini a shortening of → minimum; → black hole.

The least value attained (or attainable) by a function; the opposite of maximum.

Etymology (EN): From L. minimum “smallest” (thing), neuter of minimus “smallest,” superlative of → minor “smaller.”

Etymology (PE): Kaminé, from kamin superlative of kam “little, few; deficient, wanting; scarce” (Mid.Pers. kam “little, small, few,” O.Pers./Av. kamna- “small, few.”
Keh “small, little, slender” (related to kâstan, kâhidan “to decrease, lessen, diminish,” from Mid.Pers. kâhitan, kâstan, kâhênitan “to decrease, diminish, lessen;” Av. kasu- “small, little;” Proto-Iranian *kas- “to be small, diminish, lessen”) + -é nuance suffix.

Same as → angle of minimum deviation.

See also: → minimum; → deviation.

The minimum distance between the paths of two orbiting objects around a → primary. Such distance between an object and Earth is called Earth MOID.

See also: → minimum; → orbit; → intersection; → distance.

The amount of hydrogen necessary to form a star; more specifically the minimum mass to ignite → hydrogen fusion.
→ Hydrogen burning will start at a limit of about 0.08 Msun, or 75 → Jupiter masses. Below 0.08 Msun, the core never gets hot enough to trigger → hydrogen fusion.

→ Protostars less massive than this limit are known as → brown dwarfs or → planets if the mass is less than 13 Jupiter masses. Above 13 Jupiter masses, some minor nuclear reactions (→ deuterium burning) occur that do not provide much energy.

The minimum mass for → star formation is a critical parameter with profound astrophysical, cosmological, and even anthropic consequences.

See also: → minimum; → stellar; → mass.

1. A → quasar of lesser power compared to ordinary quasars hypothesized to exist at early cosmic times. According to some models, the Universe was reionized by a population of miniquasars powered by → intermediate-mass black holes.
   

2. Same as → microquasar.

See also: Mini a shortening of → minimum;
→ quasar.

Same as → space-time diagram.

See also: → Minkowski metric; → diagram.

The → metric that belongs to a four-dimensional → flat manifold and is given
by ds² = - dt² + dx² + dy² + dz². Three coordinates represent → space and the fourth coordinate is devoted to → time. The Minkowski metric underlies the → geometry of → special relativity. Compare → Robertson-Walker metric.

See also: In honor of Hermann Minkowski (1864-1909), Russian-born German mathematician, who introduced the concept of the four-dimensional nature of space-time; → metric.

A completely flat four-dimensional space, which contains no gravitating matter, used in the theory of special relativity.

See also: → Minkowski metric; → space-time.

A peculiar blue object near the → elliptical galaxy NGC 541 in the → galaxy cluster Abell 194. According to several pieces of evidence, the → starburst in Minkowski’s object was triggered by the → radio jet emerging from the → nucleus of the nearby → active galaxy NGC 541. This is similar to the jet-induced → star formation associated with → Centaurus A, and the radio-aligned star forming regions in powerful radio galaxies at → high redshift. Absorption and emission line measurements and broadband → SED fitting, give an age of around 7.5 Myr for Minkowski’s object.

See also: Minkowski, R., 1958, PASP, 70, 143; → object.

Lesser or smaller in amount, extent, or size.

Etymology (EN): From L. minor “lesser, smaller, junior,” from PIE base *mei- “small” (cf. L. minuere “make small;” Gk. meion “less,” minuthein “to lessen;” Skt. miyate “diminishes, declines;” O.E. minsian “to diminish”).

Etymology (PE): Kehin comparative and superlative of
keh “small, little, slender” (related to kâstan, kâhidan “to decrease, lessen, diminish,” kam “little, few; deficient, wanting; scarce,” (Mid.Pers. kam “little, small, few,” O.Pers./Av. kamna- “small, few;” from Mid.Pers. kâhitan, kâstan, kâhênitan “to decrease, diminish, lessen;” Av. kasu- “small, little;” Proto-Iranian *kas- “to be small, diminish, lessen”) + -é nuance suffix.

The axis of an ellipse that is perpendicular to the major axis at a point equidistant from the foci.

See also: → minor; → axis.

The → merging in which one of the galaxies is significantly larger than the other (mass ratios above 10). The larger galaxy will often “swallow” the smaller satellite galaxy. The swallowed galaxy can trigger disk and nuclear star formation or activate a central core with shells that surround the predator.

See also: → minor; → merger.

An obsolete name used to describe an → asteroid.

See also: → minor; → planet.

Logic: In a → categorical syllogism, the premise containing the → minor term.

See also: → major; → premisse.

Logic: In a → syllogism, the → subject of the → conclusion.

See also: → minor; → term.

For a function f defined on the interval I, the point m such that for each x on I, f(x)≥ m. See also → majorant.

Etymology (EN): From Fr. minorant, from minorer “to reduce, cut,” from L. → minor.

Etymology (PE): Kehân, from kehidan, from keh “small, little,” → minor.

The smaller number, part, or quantity of a whole.

See also: → minor; → -ity.

The faintest and the westernmost of the three stars which appear in a row and make up the → Orion’s Belt. It is a blue star of magnitude 2.23 lying 915 light-years away. Mintaka is in fact an → eclipsing binary with a period of 5.7 days. The main star has a → spectral type of O9.5 and radiates near 90,000 times the → solar luminosity. Mintaka is remarkable as regards the discovery of the → interstellar medium. The ISM was discovered by the German astronomer Johannes Hartmann (1855-1936) through the study of δ Orionis. He remarked that the calcium line at 3934 Å did not share in the periodic displacements of the lines caused by the orbital motion of the star. This
suggested that the calcium line was not from the stars but from an intervening interstellar absorbing cloud.

See also: Mintaka, from al-Mintaqah “the belt,” from al-Mintaqah al-Jauzâ’ (المنطقه‌الجوزاء) “the belt of the central one (Orion).”

1. (prep.) With the deduction of.
   

2. (adj.) → negative.
   

3. (n.) A deficiency or subtraction; the minus sign.

Etymology (EN): L. minus “less,” neuter of minor “smaller,” ultimately from PIE *mi-nu-, suffixed form of root *mei- “small;” cf. L. minuere “to diminish, lessen;” Gk. meion “less, smaller;” Av. (+ prefix *ui-) vīmītô.dantānô “with lost teeth;” O.Pers. mīθah- “damage, harm;” Mid.Pers. (+ *ui-) wmys- “to fade;” Mod.Pers. gum, gom “lost;” Ossetian minæg “weak, dim (light)” (Cheung 2007);
Skt. miyate “diminishes,” Russ. men’she “less;” O.E. minsian “to diminish.”

Etymology (PE): Kaman, from kam “little, few; deficient, wanting; scarce,” from Mid.Pers. kam “little, small, few,” O.Pers./Av. kamna- “small, few”

• suffix -an that occurs in many words, such as rowšan, rowzan “bright, window,” anjoman “assembly, association,” hâvan “mortar,” mihan “homeland, dwelling,” barzan “district, neighborhood,” rasan “rope.” These particular cases are related to Proto-Ir./Av. -ana: raocana-, hanjamana-, hāvana-, maeθana-, *varezana-, and uraisana- respectively; other cases may have a different origin, e.g. Proto-Ir. -an.

A unit of angular measurement equal to one sixtieth of a degree.
A unit of time equal to one sixtieth of an hour.

Etymology (EN): From O.Fr. minut, from M.L. minuta “minute, short note,” from L. minuta, feminin of minutus “small, minute.”

In M.L., pars minuta prima “first small part” was used by Ptolemy for “one-sixtieth of a circle,” later of an hour (next in order was secunda minuta, which became second).

Etymology (PE): Daqiqé, loan from Ar. daqiqat.

A → red giant → variable star in the constellation → Cetus, called also Omicron (ο) Ceti. Its → visual magnitude varies between 2.0 and 10.1 over a period of about 330 days, and its → spectral type between M5 and M9. Its diameter is 400-500 times that of the Sun, and it lies approximately 420 → light-years away. Mira is a → binary star, consisting of the red giant Mira A along with Mira B. It is the prototype of a class known as → long-period variables, or → Mira variables.

See also: From L. mira “wonderful,” as named by J. Hevelius (1611-1687).

A periodic → variable star with cycles 100-500 days, and of → spectral types K, M, S, and C; also called → long-period variables.

See also: → Mira; → variable.

Traditional name of → Beta Andromedae that may easily be confounded with → Merak (β Ursae Majoris).

See also: A variant of → Merak.

Same as → NGC 404.

See also: → Mirach; → ghost.

An optical phenomenon caused by → refraction of light in the lowest layers of the Earth’s → atmosphere especially in the → desert, over a hot pavement, or at → sea. Due to temperature variations, the air → density varies, leading to a spatial variation of the → index of refraction of → air. As a result, light from a single point takes more than one path to the observer and the → image of some distant object appears displaced from its true position; the image may appear distorted, inverted, or wavering.

Etymology (EN): From Fr. mirage, from (se) mir(er) “to look at (oneself), be reflected”
(from L. mirare “to wonder at, admire”) + suffix -age.

Etymology (PE): Sarâb “mirage,” literally “water point, water origin, water head,”
probably from sar “origin, beginning,” → head, + âb, → water. The similarity with Ar. serab (cf. Hebrew sharab “burning heat, parched ground”) may be fortuitous.

The eleventh of Uranus’s known satellites and the innermost of Uranus’ large moons. Its is about 470 km in diameter and orbits Uranus at about 130,000 km from its planet. It was discovered by Kuiper in 1948.

See also: Miranda is a daughter of the magician Prospero in Shakespeare’s The Tempest.

The brightest star of Perseus, with a visual magnitude of 1.8. It is a giant of spectral type F5 lying some 590 light-years away.

Etymology (EN): From Ar. al-Mirfaq (المرفق) “the elbow.”

Etymology (PE): Merfaq, from Ar. al-Mirfaq, as above.

A smooth, highly polished surface, for reflecting light, that may be plane or curved. The actual reflecting surface is usually a thin coating of silver or aluminum on glass.

Etymology (EN): From O.Fr. mireor “a reflecting glass,” earlier miradoir, from mirer “look at,” from V.L. *mirare, from L. mirari “to wonder at, admire.”

Etymology (PE): Âyene, from Mid.Pers. êwênag “mirror,” from *âdênak, cf. Khotanese âyäna- “mirror,” from Proto-Iranian *ādayana-, from prefix ā- + the root of Av. dā(y)- “to see,” didāti “sees” (cf. Mod.Pers. didan “to see,” Mid.Pers. ditan “to see, regard, catch sight of, contemplate, experience;” O.Pers. dī- “to see;” Skt. dhī- “to perceive, think, ponder; thought, reflection, meditation,” dādhye; Gk. dedorka “have seen”) + suffix -ak.

The material on which the reflecting coating is applied. It may be glass, quartz, or metal.

Etymology (EN): → mirror; blank “a piece of metal ready to be drawn, pressed, or machined into a finished object,” from M.E., from O.Fr. blanc (adj.) from Gmc; cf. O.E. blanca “white horse,” O.H.G. blanch “bright, white.”

Etymology (PE): Gerdé, → disk; âyené, → mirror.

Same as → mirror blank.

See also: → mirror; → disk.

The observation and measurement of the flatness of a mirror surface. The process generally is done before coating so as not to damage the delicate coated surface. For coated and curved surfaces, non-contact methods are often employed, generally using interference techniques.

See also: → mirror; → test.

The fourth brightest star in the constellation → Canis Major. It is a B1 → giant of magnitude 2.0 lying about 500 → light-years away. Mirzam is one of the brightest of the → Beta Cephei variable stars.

See also: From Ar. al-Mirzam (المرزم) “subordinate,” which according to the Persian astronomer Biruni (A.D. 973-1048) was a general name for a relatively fainter star lying beside a much brighter one, in this case → Sirius. Some sources have related the name of this star to Ar. al-Murzim (المرزم) “the roarer.” They claim that this name refers to the fact that the star is situated to the east of Sirius and thus “announces, heralds” imminent rising of Sirius. However, this interpretation does not seem tenable since the meaning “announcing” is far-fetched, and moreover the angular distance between Sirius and Mirzam being small, they actually rise together.

A prefix meaning “ill, mistaken, wrong, wrongly”

Etymology (EN): M.E., from O.E. mis-, cognate with M.Du. misse-, O.H.G. missa-, Ger. miss-, perhaps literally “in a changed manner,” and with a root sense of “difference, change” and thus possibly from PIE root *mei- “to change;” cf. Av. miθo- “perverted,” Skt. methati “changes, alternates, joins;” L. mutare “to change.”

Etymology (PE): Dož-, → dys-.

→ Deviation of the chain of → optical components from the optimum → alignment in an instrument which leads to → loss of → light and poor → image.

See also: → mis-; → alignment.

1. Fail to hit, reach, or come into contact with (something aimed at); to fail to do something.
   

   2. Pass by without touching.
      

   3. Feel or notice the loss or absence of.

Etymology (EN): M.E. missen, O.E. missan “fail to hit, miss (a mark); fail in what was aimed at,” akin to Du. missen, Ger. missen “to miss, fail,” from PIE *mei- “to change, go, move.”

Etymology (PE): Napidan, literally “fail attain, reach, or find,” from negation suffix na-, → not, + Av. ap- “to reach, attain;” cf. Mid./Mod.Pers. (+abi-) yâftan “to obtain, to find;” Proto-Ir. *Hap/f- “to reach, attain;” PIE *H₁ep- “to take, seize, grab;” cf. L. apiscor “to reach, to get” (Cheung 2007).

An object or weapon for throwing, hurling, or shooting. → ballistic missile.

Etymology (EN): From Fr. missile, from L. missile “weapon that can be thrown,” from missus, p.p. of mittere “to send.”

Etymology (PE): Mušak, literally “little mouse,” or “mouse like,” from a firework
explosive that was likened to a mouse, from muš, → mouse, + -ak diminutive or similarity suffix.

The unseen mass whose gravitational influence is needed to account for the way galaxies rotate, and also to bind clusters of galaxies together. It is thought to consist, in part, of giant halos of dark matter that surround the visible portions of galaxies, and similar material that invisibly occupies the intergalactic voids. Same as → hidden mass; → dark matter.

Etymology (EN): Missing, from miss “to fail to be present,” from
M.E. missen, O.E. missan; cf. O.Fris. missa, M.Du. missen, Ger. missen “to miss, fail;” → mass.

Etymology (PE): Jerm, → mass; gomšodé “lost, missing,” from gom “missing, lost” + šodé p.p. of šodan “to become” (from Mid.Pers. šudan, šaw- “to go;” Av. šiyav-, š(ii)auu- “to move, go,” šiyavati “goes,” šyaoθna- “activity; action; doing, working;” O.Pers. šiyav- “to go forth, set,” ašiyavam “I set forth;” cf. Skt. cyu- “to move to and fro, shake about; to stir,” cyávate “stirs himself, goes;” Gk. kinein “to move;” Goth. haitan “call, be called;” O.E. hatan “command, call;” PIE base *kei- “to move to and fro”); napide, p.p. of napidan, → miss.

The observed underabundance, by one or two orders of magnitude, of → dwarf galaxies orbiting → spiral galaxies compared to their number predicted by the standard model. The → cold dark matter (CDM) model predicts that dwarf galaxies are the building blocks of large galaxies like the Milky Way and should largely outnumber them. Dwarf galaxies form first, they merge into bigger and bigger galaxies, and galaxies into groups of galaxies. The dark matter halos, however, are very dense, and dwarf halos are not destroyed in the merging, resulting in their large predicted number, in numerical simulations.

See also: Probably first dealt with in an article entitled “Where Are the Missing Galactic Satellites?” (Lypin et al. 1999, ApJ 522, 82); → missing mass; → satellite; → problem.

An operation designed to carry out the goals of a specific program, such as a a space flight or voyage.

Etymology (EN): Mission, from L. missionem (nominative missio) “act of sending,” from mittere “to send,” of unknown origin.

Etymology (PE): Gosilân, from gosil, variant gosi “sending away, dismission;” Mid.Pers. wisé “to despatch” (Parthian Mid.Pers. wsys- “to despatch;” Buddhist Mid.Pers. wsydy “to despatch;” Sogdian ‘ns’yd- “to exhort”), from Proto-Iranian *vi-sid- “to despatch, send off,” from prefix vi- “apart, away, out,” + *sid- “to call” + -ân nuance suffix.

Spell a word wrongly.

See also: → mis-; → spell.

A very thin fog consisting of an aggregate of microscopic water droplets or wet hygroscopic particles (of diameter not less than 0.5 mm), in which the visibility at the earth’s surface is greater than 1 km.

Etymology (EN): O.E. mist “dimness, mist,” from P.Gmc. *mikhstaz
(cf. M.L.G. mist, Icelandic mistur), from PIE *migh-/*meigh-;
cf. Pers. miq “fog, mist;” Gk. omikhle, O.C.S. migla, Skt. megha- “cloud, mist.” → nebula.

Etymology (PE): Nezm “mist, fog,” variants nezu, nezvâ “mist,” nam “moisture, humidity;”
Av. napta- “moist,” nabās-câ- “cloud,” nabah- “sky;” cf. Skt. nábhas- “moisture, cloud, mist;” Gk. nephos “cloud, mass of clouds,” nephele “cloud;” L. nebula “mist,” nimbus “rainstorm, rain cloud;” O.H.G. nebul; Ger. Nebel “fog;” O.E. nifol “dark;” from PIE *nebh- “cloud, vapor, fog, moist, sky.”

A → glove that leaves the lower ends of the fingers bare, especially a long one made of lace or other fancy material and worn by women (Dictionary.com). → mitten.

Etymology (EN): → mitten.

Etymology (PE): Dastpuš, from dast, → hand,

• puš present stem of pušidan “to cover, to put on,” → envelope.

A hand covering enclosing the four fingers together and the thumb separately (Dictionary.com). → glove, → mitt.

Etymology (EN): M.E. miteyn, from M.Fr., O.Fr. mitaine, from from O.Fr. mite “mitten,” and from M.L. mitta.

Etymology (PE): Dasmtuž, literally “hand-shoe” (Ger. Handschuh, “glove,” literally “hand-shoe”),
from dast, → hand,

• Muž, variant of Pers. muzé “shoe,” Mid.Pers. môg “shoe, boot;” cf. Pers. paymôz- / paymôxtan “to dress;” Av. (+ pati-paitišmaoc- “to shoe;” Proto-Ir. *(h)mauc-? “to dress, clothe”
  (Cheung 2007).

To combine (substances, elements, things) into one mass, collection, or assemblage, generally with a thorough blending of the constituents.

Etymology (EN): From M.E. myxte, from O.Fr. mixte, from L. mixtus, p.p. of miscere “to mix;” cognate with Pers. âmixtan, âmiz-, as below; from PIE *meik- “to mix.”

Etymology (PE): Âmixtan, âmizidan “to mix,” from Mid.Pers. âmêz-, âmêxtan (Proto-Iranian *āmis- ,*āmiz-;
PIE *meik- “to mix”);
cf. Av. mayas- “to mix;” Skt. miks- “to mix, mingle,” miśr- “to mix, blend, combine;” Gk. misgein “to mix, mingle;” L. miscere (p.p. mixtus) “to mix;” O.C.S. meso, mesiti “to mix,” Rus. meshat, Lith. maisau “to mix, mingle.”

A merger that takes place when a → gas-poor galaxy collides with a → gas-rich galaxy.

See also: Past-participle of → mix; → merger.

In the → superheterodyne technique, the electronic component that lowers the frequency of the input signal and combines it with the signal coming from the → local oscillator to produce the → intermediate frequency signal. The lowered frequency, when amplified, has little chance to escape back into the antenna and produce feedback. Moreover, it is easier to make efficient amplifiers, filters, and other components for lower frequencies.

See also: Agent noun from → mix.

1. General: The process or result of irregular fluctuations in fluid motions on all scales from the molecular to large eddies.
   

2. Relating to → stellar interior, → mixing process.

See also: Verbal noun of → mix.

In a → turbulent flow, the average distance traveled by a → convective cell before it dissolves into its surroundings and deposits its energy. The mixing length is of the order of the → pressure scale height (H_P),
l = αH_P, where α is the → mixing length parameter. See also → mixing length theory.

See also: → mixing; → length.

In the → mixing length theory, a parameter, α, that relates the → mixing length, l, to the → pressure scale height: α = l/H_P. It is usually supposed that α is of order unity. Changes in α correspond to variations in the efficiency of the → convection, hence the transfer of heat.

See also: → mixing; → length; → parameter.

A theory dealing with heat transport by → turbulence which includes an elementary treatment of → convection. The central idea is that an unbalanced → buoyancy force drives a → convective cell to move through a distance, called the → mixing length, before the cell dissolves and joins the ambient medium. In this theory an adjustable → mixing length parameter  α is used. The theory, originally due to L. Prandtl (1925), was first applied to the Sun by L. Biermann (1932, Z. Astrophys. 5, 117).

See also: → mixing; → length; → theory.

A process whereby → angular momentum and chemical species are transported from layer to layer within a star. The main mixing processes include: → convection, → overshooting, → rotation, and → turbulence. The extent to which the interiors of stars are mixed strongly influences their evolution, age, chemical content, and the relationship between their internal and surface → chemical abundances.

See also: → mixing; → process.

Mass of water vapor per mass of dry air; expressed as grams per kilogram. → humidity

See also: → mixing; → ratio.

An aggregate of two or more substances that are not chemically combined with each other.

Etymology (EN): M.E., from L. mixtura “a mixing,” from mixtus, → mix.

Etymology (PE): Âmizé, from âmiz present stem of âmixtan, → mix.

A star of visual magnitude 2.3 in the constellation → Ursa Major, which is the second star from the end of the → Big Dipper’s handle. It forms a naked-eye double with → Alcor, lying at an angular separation of about 12 minutes of arc. Mizar is resolved into a 14’’.4 → binary star (denoted A and B) with a probable period of thousands of years. Mizar A is a nearly equal-mass, → double-lined spectroscopic binary with period 20.54 days and → eccentricity of 0.53. The two components of Mizar A (denoted Aa and Ab) are both about 35 times as luminous as the Sun, and revolve around each other in about 20 days. Similarly, Mizar B is a → spectroscopic binary with a period of 175.57 days and an eccentricity of 0.46.

Recent results suggest that Alcor is actually a binary and apparently → gravitationally bound to the Mizar system. This would make the Mizar-Alcor system a probable → sextuplet, lying at about 78 → light-years from Sun and the second closest such multiple known, after → Castor (Mamajek et al., 2010, AJ 139, 919).

See also: Mizar, from Ar. al-Mi’zar (المءزر) “loin cloth, apron, veil.”