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

A 1.2 m semi-robotic telescope located at the Roque de los Muchachos Observatory on La Palma Island (Canary Islands, Spain). It is operated by the staff of the Institute of Astronomy, University of Leuven (Belgium). The telescope uses two modern instruments HERMES: a → high-resolution optical → spectrograph, and MAIA, a three-armed camera equipped with large → charge-coupled device (CCD)s and optimized for more specific rapid variability studies. The main science drivers of the research performed on the basis of Mercator data are related to a wide range of variable phenomena with a clear focus on stellar astrophysics, in particular the stellar internal structure by means of → asteroseismology.

Named after the Flemish cartographer Gerardus Mercator (1512-1594), who studied and taught at the University of Leuven before moving to Duisburg (Germany)

1) The closest → planet to the → Sun and one of five planets visible with the naked eye. The → greatest elongation of Mercury is about 28°, making it visible at most about 112 minutes after sunset or before sunrise. It lies at a mean distance of about 0.39 → astronomical units from the Sun. Mercury is just 4,879 km in diameter, about 2.6 times smaller than the Earth. Its → orbital period is 87.97 Earth days. Mercury has a high → density, 5.4 g cm^-3, with only the Earth having a higher density among the planets. This is largely due to Mercury being composed mainly of heavy metals and rock. One → solar day on Mercury lasts the equivalent of 176 Earth days while the sidereal day (the time for 1 rotation in relation to a fixed point) lasts 59 Earth days. Mercury is nearly → tidally locked to the Sun and over time this has slowed the rotation of the planet to almost match its orbit around the Sun. Mercury also has the highest orbital → eccentricity of all the planets with its distance from the Sun ranging from 46 to 70 million km. Mercury has just 38% the → gravity of Earth, this is too little to maintain an atmosphere against → solar winds, which blow it away. The surface of Mercury which faces the Sun has temperatures of up to 427°C, whilst on the alternate side this can be as low as -173°C. Mercury's core has more iron than any other planet in the → solar system. This has to do with its formation and early life. If the planet formed quickly, increasing temperatures of the evolving Sun could have vaporized much of the existing surface, leaving only a thin shell.
2) (lower case): Metallic chemical element, also called quicksilver; symbol Hg (from L. hydrargyrum "liquid silver"). → Atomic number 80; → atomic weight 200.59; → melting point -38.842°C; → boiling point 356.58°C. Mercury was first recognized as a chemical element (in the modern sense) by the French chemist Antoine L. Lavoisier (1743-1794).

From L. Mercurius "Mercury," the Roman god, originally a god of tradesmen and thieves, from merx "merchandise."

1) Mid.Pers. Tîr the name of the planet Mercury, O.Pers. proper noun *Tira-dāta- "given by Tir" (Hellenized Tiridates), Mid.Pers. Tîr.dât the name of three Parthian Kings; Av. Tīro.nakaθwa-.
2) Jivé, variant živé, from Mid.Pers. zivik, zivandag "alive, living," from zivastan "to live," zivižn "life;" O.Pers./Av. gay- "to live," Av. gaya- "life," gaeθâ- "being, world, mankind," jivya-, jva- "aliving, alive;" cf. Skt. jiva- "alive, living;" Gk. bios "life;" L. vivus "living, alive," vita "life;" O.E. cwic "alive;" E. quick; Lith. gyvas "living, alive;" PIE base *gweie- "to live."
Simâb "liquid silver," from sim "silver" (Mid.Pers. âsīm) + âb, → water.

A narrow and elongated structure of glowing → sodium gas associated with Mercury. Mercury's thin atmosphere contains small amounts of sodium that glow when excited by radiation from the Sun. Solar photons also liberate these molecules from Mercury's surface and pushes them away. Because Mercury's gravity is too weak to hold a permanent atmosphere, when atoms are evaporated from the planet's surface, some of the atoms form a tail that points away from the Sun. In particular, the yellow glow from sodium → D line is relatively bright. First predicted in the 1980s, the tail was first discovered in 2001 (A.E. Potter et al., 2001). Many tail details were revealed in multiple observations by NASA's robotic → MESSENGER spacecraft that orbited Mercury between 2011 and 2015.

→ Mercury; → tail.

1) (v.intr.) To become combined, united, swallowed up, or absorbed; lose identity by uniting or blending.
2) (v.tr.) To cause to combine or coalesce. To combine, blend, or unite gradually so as to blur the individuality or individual identity of.
Related terms: → fuse, → coalesce. See also → merger, → mergeburst, → merger process, → merger tree, → merging, → merging galaxy, → minor merger, → mixed merger, → wet merger.

From L. mergere "to dip, immerse," probably rhotacized from *mezgo, and cognate with Skt. majj- "to dive, to sink," majjati "dives under;" Lith. mazgoju "to wash."

Taškidan, taškândan, from Gilaki tašk "tie, knot;" Tabari tešk "knot" + -idan infinitive suffix.

A hypothetical → transient event undergone by a → star due to its violent → merging with another star in a → close binary star. The release of → orbital energy causes the → envelope of the star to heat up and → inflate, causing the star to brighten considerably. Mergebursts are predicted to rival or exceed the brightest classical → novae in luminosity, but to be much cooler and redder than classical novae, and to become slowly hotter and bluer as they age.

→ merge; → burst.

1) Any combination of two or more bodies into a single body. In particular, the formation of a galaxy from the collision of two or more separate galaxies.
2) An act or instance of merging.

From → merge + -er (as in waiver).

Tašké; tašk, nouns from taškidan, → merge.

The process of collision between galaxies which leads to a single galaxy.

→ merger; → process.

A method used in → numerical simulations for studying the growth and development of galaxies and → dark matter halos. Within the currently accepted ΛCDM cosmology, dark matter halos merge from small → clumps to ever larger structures. This merging history can be traced in simulations and stored in the form of merger trees. Merger trees are necessary because a galaxy may have more than one → progenitor at an early time.

→ merger; → tree.

1) (n.) The act of joining together as one, such as galaxy → merger.
2) (adj.) That merges.

Noun from → merge.

Two or more galaxies that collide and merge into one galaxy.

→ merging; → galaxy.

1) Geography: An imaginary line on the Earth's surface joining the north and south poles at right angles to the equator. See also → local meridian, → prime meridian.
2) Astron.: An imaginary great circle on the → celestial sphere that passes through its poles and the observer's → zenith.

M.E., from O.Fr. meridien, from L. meridianus "of noon, southern," from meridies "noon, south," from meridie "at noon," altered by dissimilation from *medi die, locative of medius "mid-" + dies "day."

Nimruzân, coined by Pers. astronomer (A.D. 973-1048) in his at-Tafhim, from nim "mid-, half" (Mid.Pers. nêm, nêmag "half;" Av. naēma- "half;" cf. Skt. néma- "half") + ruz, → day, + -ân suffix denoting time and place.

Same as hour angle.

→ meridian; → angle.

A telescope with a graduated vertical scale, used to measure the declinations of heavenly bodies and sometimes to determine the time of meridian transits.

→ meridian; → circle.

An instrument designed to observe objects when they cross the meridian.

→ meridian; → observation.

The observation of a star when it crosses an observer's meridian.

→ meridian; → observation.

The moment when a celestial object crosses an observer's meridian. Same as meridian transit.

→ meridian; → passage.

Of, pertaining to, or resembling a meridian.

→ meridian + → -al.

From nimruzân, → meridian, + -i adj. suffix.

The mass motion of material within a → rotating star generated by the star's departure from spherical symmetry. For a rotating star in which → centrifugal forces are not negligible, → radiative equilibrium and → hydrostatic equilibrium cannot be satisfied. In this condition energy transfer is accomplished by means of the physical motion of material. According to → von Zeipel theorem, the heating on an → equipotential surface is generally higher in the polar direction than in the equatorial direction, which drives a large scale circulation current rising at the pole and descending at the equator. As a consequence, → mixing of material takes place in the stellar interior; see also → Eddington-Sweet time scale. The meridional circulation plays an important role in the evolution of → massive stars. The circulation current was first suggested by Arthur S. Eddington in 1926 (The Internal Constitution of the Stars, Dover Pub. Inc., New York) and subsequently quantified by P. A. Sweet (1950, MNRAS 110, 548).

→ meridional; → circulation.

Meteo.: A flow between the poles, or between the equator and the poles. A positive value indicates flow away from the equator; a negative value, flow toward the equator.

→ meridional; → flow.

In the → solar dynamo model, a magnetic field that points from the north to south or south to north.

→ meridional; → magnetic; → field.