An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



<< < -le Lag lam Lap lar lat lea leg len lev lig lim lin lin liq loa loc lon Lor low lum lun Lym > >>

Number of Results: 458
lunar node
  گره، گوزهر   
gereh (#), gowzahr (#)

Fr.: nœud   

One of the two points of intersection of the orbit of the Moon with the plane of → ecliptic. Indeed, the lunar orbit is tilted by about 5 degrees relative to the ecliptic. The revolution period of a lunar node in ecliptic is 18.61 years. Due to perturbation by the Sun, the lunar nodes slowly regress westward by 19.3° per year. See also → ascending node; → descending node.

lunar; → node.

Gereh, → node; gowzahri, related to gowzahr, → draconic month.

lunar orbit node
  گره ِ مداری ِ ماه   
gereh-e madâri-ye mâh

Fr.: nœud de l'orbite lunaire   

Same as → lunar node.

lunar; → orbit; → node.

lunar parallax
  دیدگشت ِ مانگی   
didgašt-e mângi

Fr.: parallaxe lunaire   

The apparent shift in the → Moon's position relative to the background stars when observed from different places on Earth. The first parallax determination was for the Moon, by Hipparchus (150 B.C.). He determined that one-fifth of the Sun's angular diameter corresponded to the lunar parallax between Hellespont and Alexandria.

lunar; → parallax.

lunar phase
  سیمای ِ ماه   
simâ-ye mâh (#)

Fr.: phase de la lune   

One of the various changes in the apparent shape of the Moon, because as the Moon orbits the Earth different amounts of its illuminated part are facing us. The phases of the Moon include: the → new moon, → waxing crescent, → first quarter, → waxing gibbous, → full moon, → waning gibbous, → last quarter, → waning crescent, and → new moon again.

lunar; → phase.

lunar probe
  گمانه‌ی ِ مانگی   
gomâne-ye mângi

Fr.: sonde lunaire   

A probe for exploring and reporting on conditions on or about the Moon.

lunar; → probe.

lunar recession
  دورشد ِ ماه   
duršd-e mâh

Fr.: éloignement de la lune   

The process whereby the → Moon gradually moves out into a slightly larger orbit. The → gravitational attraction of the Moon on the → Earth creates two ocean → tidal bulges on the opposite sides of our planet. The Earth rotates faster than the Moon revolves about the Earth. Therefore, the tidal bulge facing the Moon advances the Moon with respect to the line joining the centers of the Earth and the Moon. The Moon's gravity pulls on the bulge and slows down the → Earth's rotation. As a result, the Earth loses → angular momentum and the days on Earth are gradually increasing by 2.3 milliseconds per century. Since the angular momentum in the → Earth-Moon system is conserved, the Earth must impart the loss in its own angular momentum to the Moon's orbit. Hence, the Moon is being forced into a slightly larger orbit which means it is receding from the Earth. However, eventually this process will come to an end. This is because the Earth's own rotation rate will match the Moon's orbital rate, and it will therefore no longer impart any angular momentum to it. In this case, the planet and the Moon are said to be tidally locked (→ tidal locking). This is a stable situation because it minimises the energy loss due to friction of the system. Long ago, the Moon's own rotation became equal to its orbital period about the Earth and so we only see one side of the Moon. This is known as → synchronous rotation and it is quite common in the solar system. The Moon's average distance from Earth in increasing by 3.8 cm per year. Such a precise value is possible due to the Apollo laser reflectors which the astronauts left behind during the lunar landing missions (Apollo 11, 14, and 15). Eventually, the Moon's distance will increase so much that it will be to far away to produce total eclipses of the Sun.

lunar; → recession.

lunar regolith
  سنگپوش ِ ماه، ~ مانگی   
sangpuš-e mâh, ~ mângi

Fr.: régolithe lunaire   

The loose, fragmentary material on the Moon's surface. The lunar regolith has resulted from → meteorite collisions all along the Moon's history. It is the → debris thrown out of the → impact craters. The composition of the lunar regolith varies from place to place depending on the rock types impacted. Generally, the older the surface, the thicker the regolith. Regolith on young → maria may be only 2 meters thick; whereas, it is perhaps 20 meters thick in the older → highlands.

lunar; → regolith.

lunar terra
   \"خشکی ِ ماه\"   
"xoški-ye mâh"

Fr.: terre   

lunar highland.

lunar; terra "earth," → terrestrial.

lunar year
  سال ِ مانگی   
sâl-e mângi

Fr.: année lunaire   

A year based solely on the Moon's motion, containing 12 synodic months, each of 29.5306 days, that is a year of 354.3672 days. Used by Hebrews, Babylonians, Greeks, and Arabs.

lunar; → year.

lunârit (#)

Fr.: lunarite   

The rocks that make up the bright portions of the lunar surface.

From → lunar + ite a suffix used to form the names of minerals, such as hematite and malachite.


Fr.: lunaison   

The interval of a complete lunar cycle, between one new Moon and the next, that is 29 days, 12 hours, 44 minutes, and 2.8 seconds. or 29.5306 days. → synodic month.

M.E. lunacyon, from M.L. lunation-.

Mahâyand, literally "coming, arrival of the Moon," from mâhmoon + âyand "coming, arrival," present stem of âmadan "to come"; O.Pers. aitiy "goes;" Av. ay- "to go, to come," aēiti "goes;" Skt. e- "to come near," eti "arrival;" Gk ion " going," neut. pr.p. of ienai "to go;" L. ire "to go;" Goth. iddja "went," Lith. eiti "to go;" Rus. idti "to go;" from PIE base *ei- "to go, to walk."

lunisolar calendar
  گاهشمار ِ مانگی-خورشیدی   
gâhšomâr-e mângi-xoršidi

Fr.: calendrier luni-solaire   

A calendar in which the → solar year consists of 12 or 13 lunar → synodic months. Lunisolar calendars are → solar calendars, but use the lunar month as the basic unit rather than the → solar day. The 13th → embolismic month is to keep lunar and solar cycles in pace with each other. The reason is that the solar year has about 365 days, but 12 lunar months amount to 354 days, which is about 11 days short of a year. The most well-known lunisolar calendars are the Babylonian, Hebrew, and Chinese.

From luni-, from → lunar, + → solar; → calendar.

lunisolar precession
  پیشایان ِ مانگی-خورشیدی   
pišâyân-e mângi-xorši

Fr.: précession lunisolaire   

precession of the equator.

From luni-, from → lunar, + → solar; → precession.

Gorg (#)

Fr.: Loup   

The Wolf. A constellation in the southern hemisphere, located at about 15h right ascension, 45° south declination. Abbreviation: Lup; genitive: Lupi.

L. lupus "wolf," PIE *wlqwos/*lukwos; cf. Pers. gorg, as below; Gk. lykos; Albanian ulk; O.C.S. vluku; Rus. volcica; Lith. vilkas "wolf;" P.Gmc. *wulfaz (cf. O.S. wulf, O.N. ulfr, O.Fris., Du., O.H.G., Ger., E. wolf).

Gorg "wolf," Aftari dialect varg, M.Pers. gurg, O.Pers. Varkana- "Hyrcania," district southeast of the Caspian Sea, literally "wolf-land," today Iran Gorgân; Khotanese birgga-; Sogdian wyrky; Av. vəhrka-; Skt. vrka-.

Lupus Loop
  گردال ِ گرگ   
gerdâl-e gorg

Fr.: Boucle du Loup   

An large nonthermal radio source in the constellation → Lupus, identified as a very old supernova remnant. It is also an extended source of soft X-rays.

Lupus; → loop.

  ۲۱ لوتسیا   
21 Lutetia

Fr.: 21 Lutetia, 21 Lutèce   

A large → main belt  → asteroid that belongs to a sub-type of hydrated → M-type asteroids. It is an elongated body with its longest side around 130 km. The → Rosetta space probe flew by Lutetia and gathered data on it in 2008. Lutetia was discovered on November 15, 1852, by Hermann Goldschmidt (1802-1866) from the balcony of his apartment in Paris.

Named → Lutetia from L. Lutetia Parisiorum, literally "Parisian swamps," the Gallo-Roman city that was the ancestor of present-day Paris.

Lutz-Kelker bias
  ورک ِ لوتز-کلکر   
varak-e Lutz-Kelker

Fr.: biais de Lutz-Kelker   

A systematic error that can be introduced when → trigonometric parallaxes are used to calibrate a luminosity system. The bias arises when stars are selected by a lower limit in the observed parallax values. This favors the stars for which the measured parallax result is relatively too large.

Named after Th. Lutz & D.H. E. Kelker, 1973, PASP 85, 573; → bias.

luks (#)

Fr.: lux   

SI unit of illumination equal to a luminous flux of 1 lumen per square meter. SI unit of luminous incidence or illuminance, equal to 1 lumen per square meter.

From Gk. lux "light," → lumen.


Fr.: Lyman   

Theodore Lyman (1874-1954), an American physicist who was a pioneer in studying the spectroscopy of the → extreme ultraviolet region of the electromagnetic radiation.
Lyman alpha blob, → Lyman alpha forest, → Lyman alpha line, → Lyman alpha nebula , → Lyman band, → Lyman break, → Lyman break galaxy, → Lyman continuum, → Lyman continuum escape, → Lyman limit, → Lyman ghost, → Lyman series, → Lyman-Werner photon.

Named for Th. Lyman, as above.

Lyman alpha blob (LAB)
  ژیگ ِ لایمن-آلفا   
žig-e Lyman-alpha


A gigantic cloud of → hydrogen hydrogen gas emitting the → Lyman alpha line identified in → high redshift, → narrow band → surveys. LABs can span hundreds of thousands of → light-years that is larger than galaxies. Normally, Lyman alpha emission is in the ultraviolet part of the spectrum, but Lyman alpha blobs are so distant, their light is redshifted to (longer) optical wavelengths. The most important questions in LAB studies remain unanswered: how are they formed and what maintains their power? One of the largest LABs known is SSA22-LAB-01 (z = 3.1). Embedded in the core of a huge → cluster of galaxies in the early stages of formation, it was the very first such object to be discovered (in 2000) and is located so far away that its light has taken about 11.5 billion years to reach us. Recent observations of SSA22-LAB-01 using → ALMA shows two galaxies at the core of this object and they are undergoing a burst of → star formation that is lighting up their surroundings. These large galaxies are in turn at the centre of a swarm of smaller ones in what appears to be an early phase in the formation of a massive cluster of galaxies (see J. E. Geach et al. 2016, arXiv:1608.02941).

Lyman; → alpha; → blob.

<< < -le Lag lam Lap lar lat lea leg len lev lig lim lin lin liq loa loc lon Lor low lum lun Lym > >>