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

An important astronautical technique whereby a → spacecraft takes up a tiny fraction of the → orbital energy of a planet it is flying by, allowing it to change → trajectory and → speed. Since the planet is not at rest but gravitating around the Sun, the spacecraft uses both the orbital energy and the gravitational pull of the planet. Also known as the slingshot effect or → gravitational slingshot. More specifically, as the spacecraft approaches the planet, it is accelerated by the planet's gravity. If the spacecraft's velocity is too low, or if it is heading too close to the planet, then the planet's → gravitational force will pull it down to the planet. But if its speed is large enough, and its orbit does not bring it too close to the planet, then the gravitational attraction will just bend the spacecraft's trajectory around, and the accelerated spacecraft will pass rapidly by the planet and start to move away. In the absence of other gravitational forces, the planet's gravity would start to slow down the spacecraft as it moves away. If the planet were stationary, the slow-down effect would be equal to the initial acceleration, so there would be no net gain in speed. But the planets are themselves moving through space at high speeds, and this is what gives the "slingshot" effect. Provided the spacecraft is traveling through space in the same direction as the planet, the spacecraft will emerge from the gravity assist maneuver moving faster than before.

→ gravity; assist, from M.Fr. assister "to stand by, help, assist," from L. assistere "assist, stand by," from → ad- "to" + sistere "to cause to stand," from PIE *siste-, from *sta- "to stand" (cognate with Pers. istâdan "to stand").

Yâri "assistance, help; friendship," from yâr "assistant, helper, friend," from Mid.Pers. hayyâr "helper," hayyârêh "help, aid, assistance," Proto-Iranian *adyāva-bara-, cf. Av. aidū- "helpful, useful."

The → probability distribution of the → number of galaxies that a host → dark matter halo of a given mass contains. HOD is a powerful theoretical frame to populate dark matter halos with luminous galaxies. More specifically, it describes the bias between galaxies and dark matter by specifying (a) the probability P(N|M) that a halo of → virial mass M contains N galaxies of a particular class and (b) the relative spatial and velocity distributions of galaxies and dark matter within halos.

→ halo; → occupation; → distribution.

Someone who interprets literary or scriptural texts.

Agent noun from → hermeneutics

Methodology, Math.: Pertaining to a method of analyzing outcome through comparison to previously recognized patterns in the absence of an → algorithm for formal proof.

From L. heuristicus (from Gk. heuretikos "inventive," related to heuriskein "to find," from heur-) + -isticus, → -ic.

Yâftik, from yâft past tense of yâftan, yâb- "to → find" + -ik, → -ic.

A type of graphical representation, used in statistics, in which frequency distributions are illustrated by rectangles.

Histogram, from Gk. histo-, a combining form meaning "tissue," from histos "mast, loom, beam, warp, web," literally "that which causes to stand," from histasthai "to stand," from PIE *sta- "to stand" (cf. Pers. ist-, istâdan "to stand;" O.Pers./Av. sta- "to stand, stand still; set;" Skt. sthâ- "to stand;" L. stare "to stand;" Lith. statau "place;" Goth. standan); → -gram.

Nemudâr, → diagram + sotuni "column-like," from sotun "column," from Mid.Pers. stun, from O.Pers. stênâ "column," Av. stuna-, Skt. sthuna- "column."

Of, pertaining to, treating, or characteristic of → history or past events (Dictionary.com). → historical supernova.

→ history; → -al.

A supernova event recorded in the course of history before the invention of the telescope. The well recorded supernovae of this small group are SN 185, SN 1006, SN 1054 (→ Crab Nebula), SN 1181, SN 1572 (→ Tycho's star), and SN 1604 (→ Kepler's star).

→ historical; → supernova.

1) The branch of knowledge dealing with past events.
2) The record and explanation of past events and times, especially in connection with a particular people, country, period, person, etc. See: → star formation history, → historical supernova.

History, from M.E. histoire, historie, from O.Fr. estoire, histoire, from L. historia "narrative, tale, story," from Gk. historia "a learning or knowing by inquiry, record, account," from historein "to inquire," from histor "one who knows or sees, wise man, " from PIE *wid-tor-, from base *weid- "to know; to see;" cf. Pers. bin- "to see" (present stem of didan); Mid.Pers. wyn-; O.Pers. vain- "to see;" Av. vaēn- "to see;" Skt. veda "I know." Related to Gk. idein "to see," and to eidenai "to know," → idea.

Târix, from Ar., itself, according to Abu Rayhân Biruni (973-1048, in Athar al-Baqqiya), loan from Mid.Pers. mâhrôz "date," first Arabicized as murux, from which the infinitive taurix, and then târix.

The distance from the Earth to the → cosmic horizon which marks the edge of the → observable Universe. Same as → Hubble radius, → Hubble length, and → cosmic horizon.

→ Hubble; → distance.

A person having a strong interest in or concern for human welfare, values, and dignity (dictionary.com).

→ human + → -ist.

1) Lack of consistency or agreement; incompatibility; an inconsistent feature or quality.
2) Logic: The property of being inconsistent; a self-contradictory proposition (TheFreeDictionary.com).

→ in-; → consistency.

1) Lacking in consistency, agreement, or compatibility; at variance.
2) Containing contradictory elements.
4) Maths: (of two or more equations) not having one common set of values of the variables: x + 2y = 5 and x + 2y = 6 are inconsistent
5) Logic: (of a set of propositions) Enabling an explicit contradiction to be validly derived (TheFreeDictionary.com).

→ in-; → consistent.

1) A person who shows great independence or individuality in thought or action (Dictionary.com).
2) An advocate of → individualism (Dictionary.com).

→ individual; → -ist.

To be firm in a demand or course; refuse to yield (Dictionary.com).

L. insistere "stand upon, dwell upon," from → in- "upon" + sistere "take a stand," → resist.

Daristâdan "to insist" (Dehxodâ), from dar-, → in-, + istâdan "to stand," → resist.

The act or fact of insisting; the quality of being insistent.

Verbal noun of → insist.

Earnest or emphatic in dwelling upon, maintaining, or demanding something; persistent; pertinacious (Dictionary.com).

Adjective from → insist.

An astronomer, engineer, or technician who is concerned with the construction of astronomical instruments.

→ instrumental + → -ist.

The random fluctuation of voltage across a resistor caused by the thermal excitation of electrons within it, and the dissipation of power associated with these fluctuations. More generally, an intrinsic noise generated by thermal agitation of electrons by all bodies whose temperature is above 0 K. Also called → thermal noise, Johnson noise, or Nyquist noise.

Named after John Bertrand Johnson (1887-1970) and Harry Nyquist (1889-1976) Swedish-born American engineers and physicists, who did important work on thermal noise and information theory. → noise.

A person versed in the law, as a judge, lawyer, or scholar.

M.E., from M.Fr. juriste, from M.L. iurista "jurist," from L. ius "law," → just.

Dâdšenâs, literally "knower of justice," → jurisprudence.

The distance traversed by a photon between the time it is emitted and the time it reaches the observer. It is also referred to as the → look-back time.

→ light; → travel; → distance.