An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

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.

From mid- an E. combining form related to → middle; → night.

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).

→ 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.

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.

→ 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).

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.

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).

→ migrate; → -tion. Kuc "the act of moving from a dwelling, a place to another, decamping, migration."

Migrating; periodically migrating; pertaining to migration.

→ 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).

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.

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.

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;"

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.

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.

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.

→ Milky Way; → galaxy.

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

→ 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.

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

Prefix meaning one thousandth (10^-3).

From Fr., from L. mille "thiusand."

Mili-, loan from Fr.

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

→ 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.

→ 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.

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.

→ 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.

→ millimeter wave; → astronomy.