An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



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Number of Results: 732
Roche lobe overflow (RLOF)
  سرریز ِ لپ ِ رُش   
sarriz-e lap-e Roche

Fr.: débordement du lobe de Roche   

A process in a → binary system when a star fills its → Roche lobe, often by becoming a → giant or → supergiant during the later stages of → stellar evolution. When the star expands, any material that passes beyond the Roche lobe will flow onto the binary → companion, often by way of an → accretion disk. This occurs through the → inner Lagrangian point where the gravity of the two stars cancels. The RLOF is responsible for a number of phenomena including → cataclysmic variables, → Type Ia supernovae, and many → X-ray binary systems.

Roche lobe; → overflow.

  برد، سنگ   
bard (#), sang (#)

Fr.: roche   

1) A large mass of → stone forming a hill, cliff, promontory, or the like.
2) Geology: Mineral matter of variable composition, consolidated or unconsolidated, assembled in masses or considerable quantities in nature, as by the action of heat or water (

M.E. rokk(e), from O.Fr. ro(c)que, roche (cf. Sp., Provençal roca, It. rocca, M.L. rocca, V.L. *rocca, of uncertain origin.

Bard (Dehxodâ) "rock, stone," used in a large part of Western Iran, specifically in Lori and Kurd., related to Kurd. pal "rock, stone;" cf. Gk. poros "rock." Sang, → stone.

rock crystal
  بلور ِ سنگی، برد-بلور   
bolur-e sangi, bard-bolur

Fr.: cristal de roche   

Pure natural crystalline form of → silica, SiO2, which is transparent and colorless.

rock; → crystal.


Fr.: fusée   

A projectile driven by reaction propulsion that carries its own propellants. → missile = mušak (موشک).

From It. rocchetto "a rocket," literally "a bobbin," diminutive of rocca "a distaff," with reference to its shape.

rocket astronomy
  اخترشناسی با روکت   
axtaršenâsi bâ roket

Fr.: astronomie par fusée   

The study of celestial bodies in the wavelengths that are almost completely absorbed by the atmosphere, by using a rocket to carry instruments above 250 km to measure the searched for phenomena.

rocket; → astronomy.

  روکت‌شناسی، روکت‌گری   
roket šenâsi, roketgari

Fr.: fuséologie   

The science of rocket design, development, and flight.

rocket + -ry a noun suffix.

Roket šenâsi, from roket, → rocket, + šenâsi, → -logy; roketgari with suffix -gari, from -gar, → -or.


Fr.: fusée-sonde lancée à partir d'un ballon   

A rocket launched from a balloon at a pre-determined height and fired by a ground-controlled radio relay when some particular event, e.g. a solar flare, occurs.

From rocket + balloon.

From roket + lon, → ballon astronomy.

Roemer delay
  درنگ ِ رؤمر   
derang-e Rømer

Fr.: retard de Rømer   

A time delay caused by the light travel across a → dynamical system. The finite → speed of light causes a delay, for example, between the → primary eclipse and the → secondary eclipse in → binary systems.

Named after Ole Rømer (1664-1710), who discovered the finite speed of light, → Roemer's measurement; → delay.

Roemer's measurement
  اندازه‌گیری ِ رؤمر   
andâzegiri-ye Rømer

Fr.: mesure de Rømer   

The first successful measurement of the → speed of light carried out by the Danish astronomer Ole Rømer in 1675 at Paris Observatory. Astronomers knew that the mean period of revolution for Jupiter's innermost satellite → Io (Jupiter I) was 42.5 hours. During this period Io was sometimes eclipsed by Jupiter. Astronomers expected that if Io was visible at some time it must be visible 42.5 hours later. But Ole Rømer discovered that there were many irregularities in Io's orbital period. Sometimes Io appeared too early and other times too late in relation to the expected times. The irregularities repeated themselves precisely at a one-year interval, which meant that they must be connected to the Earth's rotation around the Sun. Rømer attributed this difference in time to the additional distance the light from Io had to travel at different times, and used this information to calculate the speed of light. He found that it takes light 22 minutes to traverse the Earth's orbital diameter; the correct figure was later determined to be 16 minutes and 40 seconds. Rømer was able to measure the speed of light to be 230,000 km s-1. Although this figure was very close to the currently accepted value of 300,000 km s-1, it was rejected by the scientific community of the time, who assumed it to be much too high a figure.

Ole Rømer (1664-1710); → measurement.

rontgen (#)

Fr.: roentgen   

A unit of radiation exposure defined as a charge release rate of 258 micro-coulombs per kilogram of air.

Named after the German physicist Wilhelm Konrad Röntgen (1845-1923), one of the early investigators of radioactivity.

rontgeniom (#)

Fr.: roentgenium   

An artificially produced radioactive chemical element; symbol Rg. Atomic number 111; mass number of most stable isotope 272; melting point, boiling point, specific gravity, and valence unknown.

Named after the German physicist Wilhelm Konrad Röntgen (1845-1923), one of the early investigators of radioactivity.

velgard (#)

Fr.: vagabond   

A vagabond or tramp. A dishonest or unprincipled person.

Perhaps short for obsolete roger "begging vagabond."

Velgard "vagabond, roamer, tramp."

rogue planet
  سیاره‌ی ِ ولگرد   
sayyâre-ye velgard

Fr.: planète vagabonde   

Same as → free-floating object.

rogue; → planet.

roll cloud
  ابر ِ لوله‌وار   
abr-e lule-vâr

Fr.: nuage en rouleau   

A low, horizontal, tube-shaped, and relatively rare type of → arcus cloud.

M.E. scroll, inscribed scroll, register, cylindrical object < OF ro(u)lle M.E. rolle, from O.Fr. roule, rolle, from M.L. rotulus "a roll of paper," from L. rotula "small wheel," diminutive of rota "wheel;" → cloud.

Abr, → cloud; lule-vâr "tube like," from lulé "tube, pipe," related to lulidan "to roll, rotate; to stir, vibrate" + -vâr suffix of resemblance.

Rolle's theorem
  فربین ِ رول   
farbin-e Rolle

Fr.: théorème de Rolle   

If a function f(x) is → continuous on an interval [a,b] and is → differentiable at all points within this interval, and vanishes at the end points x = a and x = b, that is f(a) = f(b) = 0, then inside [a,b] there exists at least one point x = c, a < c < b, at which the derivative f'(x) vanishes.

Named after Michel Rolle (1652-1719), a French mathematician; → theorem.

Roman calendar
  گاهشمار ِ رومی   
gâhšomâr-e Rumi

Fr.: calendrier romain   

Any of several → lunar calendars used by Romans before the advent of the → Julian calendar in 46 B.C. The original Roman calendar, which had 10 months and 304 days, went back to the Greek calendar, although Romulas, the ruler of Rome, is given credit for starting the Roman calendar. Originally, the Roman calendar started the year in March with the → vernal equinox. The Roman calendar went through several changes from 800 B.C. to the Julian calendar. The 800 B.C. calendar had 10 months and a winter period, with a year of 304 days. In this calendar, the first month, March, was followed by Aprilis, Maius, Junius, Quintilis, Sextilis, September, October, November, December, and Winter. The months starting with and following Quintilis all used the Latin numbers for names. Finally, for political reasons, the Romans made a change around 150 B.C. when they started using January as the beginning of their calendar year. Around 700 B.C. the 304 day calendar was expanded to 355 days by adding the months of February and January to the end of the year. Later in 450 B.C., January was moved in front of February. Finally, in 150 B.C. the Romans began to use January as the beginning of the calendar year. This calendar was replaced by the Julian calendar in 46 B.C.

From L. Romanus "of Rome, Roman," from Roma "Rome," of uncertain origin.

Roman numeral system
  راژمان ِ عددهای ِ رومی   
râžmân-e adadhâ-ye Rumi

Fr.: numération romaine   

A → number system in which letters represent numbers, still used occasionally today. The cardinal numbers are expressed by the following seven letters: I (1), V (5), X (10), L (50), C (100), D (500), and M (1,000). If a numeral with smaller value is written on right of greater value then smaller value is added to the greater one. If it is preceded by one of lower value, the smaller numeral is subtracted from the greater. Thus VI = 6 (V + I), but IV = 4 (V - I). Other examples are XC (90), CL (150), XXII (22), XCVII (97), CCCXCV (395). If symbol is repeated then its value is added. The symbols I, X, C and M can be repeated maximum 3 times. A dash line over a numeral multiplies the value by 1,000. For example V- = 5000, X- = 10,000, C- = 100,000, and DLIX- = 559,000.

numeral; → system.

zâq (#)

Fr.: corbeau freux   

A common Old World gregarious crow (Corvus frugilegus).

M.E., from O.E. hrôc; akin to O.H.G. hruoch "crow."

Zâq, from Mid.Pers. zâγ "crow."

rišé (#)

Fr.: racine   

1) Math.: A quantity that, when multiplied by itself a certain number of times, produces a given quantity. For example, since 3 × 3 × 3 × 3 = 81, 3 is a fourth root of 81.
2) Math.: A solution to an equation f(x) = 0. We say that x0 is a root or zero of a → polynomial if f(x0) = 0. For example, the roots of the equation x2 - 9 = 0 are +3 and -3.
3) In → graph theory, a special → vertex that turns a → tree into a → rooted tree or a graph into a → rooted graph.

From M.E., from O.E. rot, from O.N. rot "root;" cf. O.H.G. wurz "plant, herb;" Ger. Wurz; cognate with L. radix, radius "staff;" Gk. rhiza "root;" Albanian rrânzë "root;" PIE base *u(e)rad- "twig, root."

Rišé "root" (dialectal Tabari rexa; Kurd. regez, riše), from Mid.Pers. rêšak "root," maybe ultimately related to PIE *u(e)rad-, as above, although the Skt. offshoot is absent.

root mean square (rms)
  ریشه‌ی ِ چاروشی ِ میانگین، ~ ِ دوم ِ ~   
riše-ye câruši-ye miyângin, ~ dovom-e ~

Fr.: valeur quadratique moyenne   

The square root of the arithmetic mean of the squares of the numbers in a given set.

root; → mean; → square.

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