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

Occurring in nature; not artificially prepared. → nature.

Adj. of → nature.

Any frequency of small-amplitude oscillation for a system with a position of stable equilibrium and in the absence of external forces. In other words, the frequency of → free oscillation. Also called characteristic frequency.

→ natural; → frequency.

The → sciences, as → botany, → mineralogy, or → zoology, dealing with the study of all objects in → nature: used especially in reference to the beginnings of these sciences in former times (Dictionary.com).

→ natural; → history.

Linguistics: A language that has evolved naturally as a means of communication among people, as opposed to → artificial language and → formal language (Dictionary.com).

→ natural; → language.

The broadening of any spectral line due to the fact that excited levels have mean lives, which, by virtue of the uncertainty principle, implies a spread in the energy values.

→ natural; → line; → broadening.

The logarithm in which the → base is the → irrational number e = 2.718281828.... Also called → Napierian logarithm. The natural logarithm is denoted ln, an abbreviation of logarithmus naturalis. Natural logarithms are related to → common logarithms through: ln x = (1/M) log x, with M = (1/ln 10) ≅ 0.434294.

→ natural; → logarithm.

Either a member of the set of positive integers 1, 2, 3, ..., or the set of non-negative integers 0, 1, 2, 3, ... There seems to be no general agreement about whether to include 0 in the set of natural numbers.

→ natural; → number.

Of a body or system, the period of → free oscillation.

→ natural; → period.

A resonance such that the period of the driving force is the same as the natural period of the system.

→ natural; → resonance.

A solar system → object that → revolves around a → primary body and is not man made.

→ natural; → satellite.

A science that deals with matter, energy, their interrelations and transformations, In other words, natural sciences are concerned with physical processes observable in nature. They can be divided into physical and biological sciences.

→ natural; → science.

Physical units of measurement defined in terms of universal physical constants in such a manner that some chosen physical constants (e.g. the speed of light, Planck's constant, Boltzmann's constant, etc.) are equal to unity. The use of natural units allows these constants to be omitted from mathematical equations, leading to simpler calculations.

→ natural; → unit.

Uranium as found in nature. It contains 0.7% uranium-235, 99.3% uranium-238, and a trace of uranium-234 by weight.

→ natural; → uranium.

Philosophy: 1) The view of the world that takes account only of natural elements and forces, excluding the supernatural or spiritual.
2) The belief that all phenomena are covered by laws of science and that all teleological explanations are therefore without value (Dictionary.com).

→ natural; → -ism.

The natural world as it exists without human beings or civilization.

M.E. natur(e), from O.Fr. nature from L. natura "the things at the outset, as it was when brought into existence; conditions of birth; essence, natural qualities," from natus "born," p.p. of nasci "to be born," from PIE *gen- "to give birth, beget," cognate with Pers. zâdan "to give birth," as below.

Zâstâr, literally "birth," from zâst past stem of [Dehxodâ] zâstan, variant of zâdan "to bring forth, give birth;" (Lâsgardi, Sorxeyi, Aftari) nestor "barren, sterile" (Mid.Pers. zâtan; Av. zan- "to bear, give birth to a child, be born," infinitive zazāite, zāta- "born;" cf. Skt. janati "begets, bears;" L. gignere "to beget," nasci "to be born," as above, PIE base *gen- "to give birth, beget") + suffix -âr (forming verbal nouns as in raftâr, kerdâr, goftâr, didâr, jostâr, and so on; or forming accusative nouns, as in gereftâr, koštâr, etc.).

The branch of practical astronomy concerned with the determination of position and direction on sea by observation of celestial objects.

Nautical, from M.Fr. nautique, from L. nauticus "pertaining to ships or sailors," from Gk. nautikos, from nautes "sailor," from naus "ship," from PIE *nau- "boat;" cf. Pers. nâv "ship;" O.Pers./Av. *nāv-, O.Pers. nāviyā- "fleet;" Skt. nau-, nava- "ship, boat;" → astronomy.

Axtaršenâsi→ astronomy; daryâ-navardik, relating to daryâ-navardi "sea navigation," from daryâ "sea" (Mid.Pers. daryâp variant zrah; O.Pers. drayah-; Av. zrayah- "sea;" cf. Skt. jráyas- "expanse, space, flat surface") + navardi, noun of navardidan, navardan "to travel, walk, pass by and over" + -ik, → -ic.

One of the three twilight phases which is the period before sunrise and after sunset when the center of the Sun's disk is between 6° and 12° below the horizon. This twilight phase is followed or preceded by → civil twilight. See also → astronomical twilight. In clear weather conditions, the horizon is faintly visible during this phase. Many of the brighter stars can also be seen, making it possible to use the position of the stars in relation to the horizon to navigate at sea. This is why it is called nautical twilight.

→ nautical astronomy; → twilight.

One of a set of → differential equations that describes the motion of a → fluid as a function of → pressure, → density, total external force, and → viscosity. See also → Euler equation.

Named after Claude-Louis Navier (1785-1836), a French engineer and physicist, and George Gabriel Stokes, → stokes; → equation.

Same as → nautical astronomy.

Navigational, adj. of navigation, from L. navigationem (nom. navigatio), from navigatus, p.p. of navigare "to sail, steer a ship," from navis "ship," cognate with Pers. nâv "ship," as below, + root of agere "to drive," → act; → astronomy.

Axtaršenâsi→ astronomy; nâvrâni "navigation," from nâv "ship;" O.Pers./Av. *nāv-, O.Pers. nāviyā- "fleet;" cf. Skt. nau-, nava- "ship, boat" + râni verbal noun of rândan "to drive, to cause to go," causative of raftan "to go, walk, proceed" (present tense stem row-, Mid.Pers. raftan, raw-, Proto-Iranian *rab/f- "to go; to attack").

Tide which occurs during the → first quarter and → third quarter of the → Moon when the pull of the Sun is at → right angles to that of the Moon.

Neap, from M.E. neep, from O.E. nepflod "neap tide" + → tide.

Kehkešan "small tide," from keh- "small, little," → low, + kešand, → tide.