An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



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Number of Results: 450
heliacal rising
  بر‌آیش ِ هورانه   
barâyeš-e hurâné

Fr.: lever héliaque   

The first appearance of a star following a period of invisibility due to its conjunction with the Sun. → heliacal rising of Sirius.

heliacal; → rising.

heliacal rising of Sirius
  بر‌آیش ِ هورانه‌ی ِ تیشتر   
barâyeš-e hurâne-ye Tištar

Fr.: lever héliaque de Sirius   

The first rising of → Sirius at dawn shortly before → sunrise. The heliacal rising of Sirius played a significant role in ancient Egypt by heralding the annual flooding of the Nile. The event took place some 70 days after the star had been seen for the last time in the western horizon at sunset. The heliacal rising of Sirius and its association with the rebirth of the Nile was so important that it marked the start of the Egyptian calendar year. At the time, the heliacal rising occurred in early July, as seen from the ancient capital of Memphis. But due to the → precession of the equinoxes the star now reappears in early August in Egypt. The date depends on the latitude (assuming transparent skies), being later for higher latitudes. For latitude 48° it occurs on about August 19.

heliacal; → rising; → Sirius.

heliacal setting
  فروشد ِ هورانه   
forušod-e hurâné

Fr.: coucher héliaque   

The last visible setting of a star below the western horizon just after sunset entering into a conjunction with the Sun.

heliacal; → setting.


Fr.: hélicité   

1) In particle physics, the projection of the spin of an elementary particle on the direction of momentum.
2) In fluid mechanics, → kinetic helicity.
3) In magnetohydrodynamics, → magnetic helicity.

From → helix + → -ity.

  هور-، خور-، خورشید-   
hur- (#), xor- (#), xoršid- (#)

Fr.: hélio-   

A combining form of Gk. helios "sun."

Helio-, combining form of from Gk. helios "sun;" cognate with Persian hur "sun", variant xor and xoršid (Av. hvarə-xšaēta- "shining sun"); Mid.Pers. xvar "sun;" Av. hû-, hvar- "sun;" Skt. surya-; L. sol; O.H.G. sunna; Ger. Sonne; E. sun; PIE *sawel- "sun."

  هورمرکزی، خورشیدمرکزی   
hurmarkazi (#), xoršid markazi (#)

Fr.: héliocentrique   

Having or representing the Sun as a center. → heliocentric cosmology, → heliocentric gravitational constant, → heliocentric Julian Day, → heliocentric parallax, → heliocentric system.

helio- + → center + → -ic.

heliocentric cosmology
  کیهان‌شناسی ِ هورمرکزی   
keyhânšenâsi-ye hurmarkazi (#)

Fr.: cosmologie héliocentrique   

A model of the Universe in which the Sun was centrally located.

heliocentric; → cosmology.

heliocentric gravitational constant
  پایای ِ گرانشی هورمرکزی   
pâyâ-ye gerâneši-ye hur-markazi

Fr.: constante gravitationnelle héliocentrique   

A parameter representing the product of the → gravitational constant by the → solar mass. It is 13.27 x 1019 m3 s-2.

heliocentric; → gravitational; → constant.

Heliocentric Julian Date
  گاهداد ِ ژولی‌ین ِ هورمرکزی   
gâhdâd-e žulian-e hurmarkazi

Fr.: date julienne héliocentrique   

The → Julian Date referenced to the center of the → Sun. Since the Earth revolves around the Sun, and since light travels at a finite speed, observations of a given object taken at different positions in the Earth's orbit are not equivalent, and so a correction for Earth's orbit around the Sun is required. Left uncorrected, the time of an observational event measured by Earth clocks will vary by 16.6 minute over the course of a year. If not properly accounted for, this can lead to a spurious signal in a → periodogram.

heliocentric; → Julian Date.

heliocentric parallax
  دیدگشت ِ هورمرکزی   
didgašt-e hurmarkazi

Fr.: parallaxe héliocentrique   

The parallax of a celestial body when viewed from two points in the Earth's orbit around the Sun. More specifically, the angular difference in a celestial object's position as seen from the center of the Sun and the center of the Earth. Also called → annual parallax.

heliocentric; → parallax.

heliocentric system
  راژمان ِ هورمرکزی   
râžmân-e hurmarkazi

Fr.: système héliocentrique   

A system in which the Sun is assumed to lie at its central point while the Earth and other bodies revolve around it.

heliocentric; → system.

hurnegâšt (#)

Fr.: héliogramme   

A record made by a → heliograph.

helio-; + → -gram.

hurnegâr (#)

Fr.: héliographe   

1) An instrument for photographing the Sun, consisting of a camera and a specially adapted telescope.
2) A simple device using a mirror to reflect sunlight to a distant observer. By moving the mirror, flashes of light can be used to send coded messages. The heliograph was a highly effective instrument for instantaneous optical communication over 80km or more in the 19th century.
3) Meteo.: An instrument which records the duration of sunshine and gives a quantitative measure of the amount of sunshine.

helio-; + → -graph.

hursanj (#)

Fr.: héliomètre   

An instrument used to measure the angular separation of two stars that are too far apart to be included in the field of view of an ordinary telescope.  The instrument was originally designed for measuring the variation of the Sun's diameter at different seasons of the year.

helio- + → -meter.


Fr.: héliopause   

The edge of the solar system where the pressure of the → solar wind balances that of the → interstellar medium plasma. In other words, the surface boundary that separates the → heliosphere from interstellar space. It is estimated to be situated 100 → astronomical units or more from the Sun. A → bow shock likely forms as the interstellar medium wind approaches the heliosphere and is deflected around the heliosphere, forcing it into a teardrop-shaped structure with a long, comet-like tail.

From → helio- + pause "break, cessation, stop," from M.Fr. pause, from L. pausa "a halt, stop, cessation," from Gk. pausis "stopping, ceasing," from pauein "to stop, to cause to cease."

Hurmarz, from hur, → helio-, + marz "frontier, border, boundary," → frontier.


Fr.: héliosismologie   

The branch of astrophysics that investigates the interior structure of the Sun by studying its surface wave oscillations. See also → asteroseismology and → stellar pulsation. The surface of the Sun vibrates much like a bell. A piano has 88 keys or musical tones, whereas the Sun has millions of notes. These vibrations are the result of internal pressure waves that reflect off the → photosphere and repeatedly cross the solar interior. They are detected through the → Doppler shift of absorption lines formed in the photosphere. Because these vibrations make the solar surface move up and down, analysis of the surface patterns is used to study conditions far below the Sun's surface. The mean period of the vibrations is about five minutes, which corresponds to a speed of 0.5 km s-1 or a frequency of about 3 mHz. See also → p mode.

From → helio- + → seismology.


Fr.: héliogaine   

The region located between the → termination shock and the → heliopause where the turbulent and hot → solar wind is compressed as it passes outward against the interstellar wind.

Heliosheath, from → helio- + sheath, from O.E. sceað, scæð; cf. M.Du. schede, Du. schede, O.H.G. skaida, Ger. Scheide "scabbard."

Hurniyâm, from hur- "sun," → helio-, + niyâm "sheath," from Proto-Iranian *nigāma-, from ni- "down; into," → ni- (PIE), + gāma- "to go, to come" (Av. gam- "to come; to go," jamaiti "goes;" O.Pers. gam- "to come; to go;" Mod./Mid.Pers. gâm "step, pace," âmadan "to come;" cf. Skt. gamati "goes;" Gk. bainein "to go, walk, step;" L. venire "to come;" Tocharian A käm- "to come;" O.H.G. queman "to come;" E. come; PIE root *gwem- "to go, come"); cf. Skt. nigamá- "insertion, incorporation."

hursepehr (#)

Fr.: héliosphère   

The vast, three-dimensional region of space around the Sun filled with the → solar wind and the remnant of the → solar magnetic field carried in it. It is bounded by the → heliopause, which is estimated to be 100 → astronomical units or more from the Sun. The radius of the heliosphere is expected to vary with the → solar cycle. The heliosphere may be very elongated owing to the presence of an interstellar wind of neutral hydrogen flowing from the direction of the Galactic center.

From → helio- + → sphere.


Fr.: héliostat   

An instrument consisting of a mirror moved by clockwork for tracking the movement of the Sun and reflecting the sunlight into a stationary solar telescope. A heliostat is similar to a → coelostat.

Heliostat, from → helio- + -stat prefix denoting something that stabilizes, keeps, fixes, from -stata, from Gk. -states "one that causes to stand," or statos "standing," from *sta- "to stand."

Hurdâštâr, from hur-, → helio- + dâštâr "holder, maintainer," from dâštan "to hold, maintain; to have; to possess;" Mid.Pers. dâštan; O.Pers./Av. dar- "to hold, keep back, maintain, keep in mind;" cf. Skt. dhr-, dharma- "law;" Gk. thronos "elevated seat, throne;" L. firmus "firm, stable;" Lith. daryti "to make;" PIE base *dher- "to hold, support."

helium (#)

Fr.: hélium   

Chemical element; symbol He; atomic number 2; atomic weight 4.0026; melting point below -272°C at 26 atmospheres pressure; boiling point -268.934°C at 1 atmosphere pressure.

Helium, from Gk. helios "sun;" cognate with Persian hur "sun", variant xor; Mid.Pers. xvar "sun;" Av. hû-, hvar- "sun;" Skt. surya-; L. sol; O.H.G. sunna; Ger. Sonne; E. sun; PIE *sawel- "sun." The element was discovered by spectroscopy during a solar eclipse in the Sun's chromosphere in 1868 by the French astronomer Pierre-Jules-Cesar Janssen (1824-1907).

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