An Etymological Dictionary of Astronomy and Astrophysics
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فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory

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perigee full Moon
  پرمانگ ِ پیرازم   
pormâng-e pirâzam

Fr.: pleine lune de périgée   

The → full Moon when our natural satellite is at its closest approach to the Earth. Perigee full Moons are as much as 14% larger and 30% brighter than → apogee full Moons. Also called perigee-syzygy full Moon, super full Moon, and → supermoon. The Supermoon on November 14, 2016, was the closest (356,523 km) a Full Moon has been to Earth since January 26, 1948. The next time a Full Moon is even closer to Earth (356,448 km) will be on November 25, 2034.

perigee; → full; → moon.

perigee-syzygy full Moon
  پرمانگ ِ پیراهور-یوجان   
pormâng-e pirâhur-yujân

Fr.: lune de périgéé-syzygie   

perigee full Moon.

perigee-; → syzygy; → full; → moon.

perihelion
  پیراهور   
pirâhur

Fr.: périhélie   

The nearest point to the Sun in an orbit around the Sun; opposite of → aphelion.

Perihelion, from L. perihelium, from → peri- + helios "sun," cognate with L. sol, Skt. surya, Av. hvar-, Mod.Pers. xor, hur, O.H.G. sunna, Ger. Sonne, E. sun; PIE *sawel- "sun".

Pirâhur, from pirâ-, → peri-, + hur "sun," as above;

perihelion advance
  پیشرفت ِ پیراهور   
pišraft-e pirâhur

Fr.: avance du périhélie   

advance of perihelion.

advance of perihelion.

perihelion distance
  اپست ِ پیراهوری   
apest-e pirâhuri

Fr.: distance au périhélie   

The distance between the → Sun and an → object in orbit around it when they are at their closest approach.

perihelion; → distance.

perihelion precession
  پیشایانِ پیراهوری   
pišâyân-e pirâhuri

Fr.: précession du périhélie   

advance of perihelion.

perihelion; → precession.

perijove
  پیراهرمز   
pirâhormoz

Fr.: périjove   

The → point in the → orbit of a → satellite of → Jupiter that is nearest to Jupiter's center. → apojove.

peri- + jove, from L. Jovius "Jupiter," → Jovian.

peril
  سیج   
sij (#)

Fr.: péril   

1) Exposure to injury, loss, or destruction; grave risk; jeopardy; danger.
2) Something that causes or may cause injury, loss, or destruction (Dictionary.com).

M.E., from O.Fr. peril "danger, risk," from L. periculum "an attempt, trial; risk, danger," related to experiri "to try," cognate with Gk. peria "trial, attempt," empeiros "experienced;" O.Ir. aire "vigilance;" Goth. ferja "watcher;" O.E. fær "danger; fear."

Sij "trouble;" Mid.Pers. sêj "danger, trouble," sêjômand "dangerous;" Av. iθyejah- "trouble, danger," iθyejahvant- "full of danger, hazardous;" cf. Skt. tyajas- "difficulty, danger."

perilune
  پیراماه   
pirâmâh

Fr.: périlune   

The point in a lunar orbit that is nearest to the moon. Same as → pericynthion.

From → peri- + lune, from L. luna "moon;" → lunar.

Pirâmâh, → apocynthion.

perimeter
  پیرامون   
pirâmun (#)

Fr.: périmètre   

The total outer boundary of a two-dimensional figure.

peri- + → -meter.

period
  دوره   
dowré (#)

Fr.: période   

Physics: The duration of one complete cycle of an oscillation; the reciprocal of the frequency.
Astro.: The amount of time an astronomical body takes to complete an orbit.

From M.E. periode, from M.Fr., from M.L. periodus "recurring portion, cycle," from L. periodus "a complete sentence," from Gk. periodos "rounded sentence, cycle, circuit, period of time," literally "going around," from → peri- "around" + hodos "way, journey;" cognate with L. cedere "to go, yield."

Dowré, from dowr, from Ar. daur "age, time; revolution."

period derivative
  واخنه‌ی ِ دوره   
vâxane-ye dowré

Fr.: dérivée de la période   

The rate at which the rotation period of a → pulsar changes over time. This quantity, dP/dT, can range from as small as 0.05 picoseconds per year (1.5 x 10-21 seconds per second) to as large as about 10 milliseconds per year (4.2 x 10-10 seconds per second). For the → Crab pulsar, the period derivative is 4.2 x 10-13 s s-1, implying a decrease in the star's → rotation energy of about 4.5 x 1038 erg s-1. Period derivative is a very important parameter for the determination of the pulsar age.

period; → derivative.

period-luminosity relation
  باز‌آنش ِ دوره-تابندگی   
bâzâneš-e dowré-tâbandegi

Fr.: relation période-luminosité   

A → correlation between the periods and luminosities of → Cepheid variable stars: Cepheids with longer periods are intrinsically more luminous than those with shorter periods. The relation was discovered by Henrietta Leavitt in 1912 when studying Cepheids in the → Small Magellanic Cloud. Once the period of a Cepheid variable is determined from observations, the period-luminosity relation can be used to derive its luminosity. Since luminosity is a function of → distance, the distance can then be calculated with the luminosity. The period-luminosity relation is an invaluable tool for the measurements of distances out to the nearest galaxies and thus for studying the structure of our own Galaxy and of the Universe.

period; → luminosity; → relation.

period-mean density relation
  باز‌آنش ِ دوره-چگالی ِ میانگین   
bâzâneš-e dowré-cagâli-ye miyângin

Fr.: relation période-densité moyenne   

A relation that gives a rough estimate of the oscillation period of a → pulsating star as a function of its mean density. This relation is obtained by considering how long it would take a sound wave to travel across the diameter of a model star: Π ≅ (3π/2γGρ)1/2, where ρ is the mean density, γ the ratio of → specific heats (Cp/Cv), and G the → gravitational constant. This relation shows that the pulsation period of a star is inversely proportional to the square root of its mean density. And this is the reason why the pulsation periods decrease along the → instability strip from the luminous, very tenuous → supergiants to the faint, very dense → white dwarfs.

period; → mean; → density; → relation.

periodic
  دوره‌ای   
dowreyi (#)

Fr.: périodique   

Recurring at regular intervals of time.

Adjective of → period.

periodic comet
  دنباله‌دار ِ دوره‌ای   
dombâledâr-e dowreyi

Fr.: comète périodique   

A comet with a period of less than 200 years. Also called short-period comet.

periodic; → comet.

periodic function
  کریای ِ دوره‌ای   
karyâ-ye dowreyi

Fr.: fonction périodique   

A function f(x) if for all x, f(x + P) = f(x), where P is a positive constant. The least value of P > 0 is called the period of f(x).

periodic; → function.

periodic motion
  جنبش ِ دوره‌ای   
jonbeš-e dowreyi

Fr.: mouvement périodique   

Any motion that recurs in identical forms at equal intervals of time.

periodic; → motion.

periodic system
  راژمان ِ دوره‌ای   
râžmân-e dowreyi

Fr.: système périodique   

Arrangement of the → chemical elements in the → periodic table.

periodic; → system.

periodic table
  جدول ِ دوره‌ای   
jadval-e dowreyi (#)

Fr.: tableau périodique   

An arrangement of the → chemical elements in order of their → atomic numbers in such a way as to demonstrate periodic similarities and trends in physical and chemical properties. Elements with similar properties are arranged in the same column (called a group), and elements with the same number of → valence electrons, or number of electrons in the outer shell, are arranged in the same row (called a period). Under the latest recommendations from IUPAC (the International Union of Pure and Applied Chemistry), the groups are labelled 1 to 18 from left to right (1988, Pure and Applied Chemistry 60, 431). Also called Mendeleev's table.
The periodic table was introduced by Dmitri Ivanovich Mendeleev (1834-1907) in 1869, who originally arranged them in order of their → atomic weights. Using the table, it was possible for Mendeleev to correct some of the atomic weights (e.g. that of beryllium) and to predict the properties of a number of elements yet to be discovered (e.g. gallium, scandium, and germanium). The British physicist Frederick Soddy (1877-1956) showed that the loss of an → alpha particle reduces the nuclear charge by two and hence lowers the atomic number by two and the position of the element in the periodic table by two groups.

periodic; → table.

<< < -es -iv -ti 21- a p abe abs abs acc acc acc act act ada adi ads aes Age Alb Alf ali all alp alt ama amp ana ang ang ann ano ant ant ape apo app app arb are ari art ass ast ast ast Atl ato ato Aug aut awa azi bac bal Bar Bar Bay bea Bep Bet BIC bij bin bio bir bla bla blu blu bol Boo bou Bq bre bri bub B[e cal cal can car car Cas cat cau cel cen Cer cha cha cha che chi CI cir cir cla cle clo clu co- cob coh col col col com com com com com com com com Com con con con con con con con con con con con con coo cor cor cor cos cos cos cou cov cra cri cro cry cum cur cyc d'A dar dat DC dea dec dec dec def def deh Del den dep des det deu dia dif dif dif dim dip Dir dis dis dis dis dis div dom dos dou dri Dum dus dyn dyn ear eas ecl Edd eff Ein eje ele ele ele ele eli emb emi Enc ene ens eph epo equ equ eru eth Eul eve evo exc exc exi exo exp exp ext ext Fab fai Fan fea fem fer fie fil fir fir fla flo flu foc For for fos fra fre fre fro fun g m Gal gal gal gas gau gel gen geo geo geo gho gla gno gra gra gra gra Gre Gre gro gyr had hal har Har HD hea hel hel Her Her Hic hig hip hol hor hos hov Hub hun hyd hyd Hyd hyp IC ide ill ima imp imp inc inc ind ind inf inf inf inf inj ins ins int int int int int int int int inv Io ion iro isl iso iso Jal JHK Jul jur Kel Kep kin kne L2 Lag lam Lap lar lat law Lec len Lep lib lig lin lin lin liq lit loc log lon los low lum lun lux Lyr mac mag mag mag mag mag maj man Mar mas mas mat May mea mec mel mer mes met met met mic mid mil Min Mir mix mod mod mom moo mor mov mul mur Na nar nat nea neg Nes neu New New Nic nod non non non Nor nov nuc nul num OB obl obs occ Ock off Ohm on- ope opi opt opt orb orb ord Ori ort OSI out ove ozo pal pan par par par par pat pec pen per per per per per Pfu pha pho pho pho phy pie pix Pla pla pla pla Pli Poi pol pol pol pol por pos pos pow pre pre pre pre pri pri pri pro pro pro pro pro pro Pro pub pul pyr qua qua qua qua qui rad rad rad rad rad rad rak ran rat Ray rea rec rec rec red ref ref reg reg rel rel rem rep res res res ret rev Rho Rie ril riv rog Ros rot rul S A Sag sam sat sca sca Sch Sco Sec sec sec seg sel sem sen set sha SHB sho sib sid sil sim sin sit sky slo Sne Soc sol sol sol sol son sou spa spa spe spe spe spe sph spi spo Squ sta sta sta sta ste ste ste sto str str str sub sub sub sum sup sup sup sup sur sus sym syn T d tap tec tem ten tes the the the the thi thr tid tim tip ton tor tow tra tra tra tra tri tri tru tub tur two Typ ult un- und uni uni uno upp urg UX Van var veg vel ver vib vio vir vis Voi vow wan wat wav WC wea wel whi Wil wir WNh wor X-r yel Z C zer ZZ > >>