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

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.

One of the stars in the Pleiades with a visual magnitude 4.17. It is a giant of spectral type B6 lying at a distance of about 1400 light-years.

Merope was one of the seven Pleiades, daughters of the Titan Atlas.

A → prime number of the form 2^p - 1, where p is a prime. As of February 2013, 48 Mersenne primes are known. The largest known prime number is 2^57,885,161 - 1. Each prime gives rise to an even → perfect number.

Marin Mersenne (1588-1648), French theologian, philosopher, mathematician and music theorist; → prime.