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

A disk or cylindrical part tightly fitting and moving within a cylinder, either to compress or move a fluid collected in the cylinder, as air or water, or to transform energy imparted by a fluid entering or expanding inside the cylinder, as compressed air, explosive gases, or steam, into a rectilinear motion usually transformed into rotary motion by means of a connecting rod (Dictionary.com).

From Fr. piston, from M.Fr. piston "large pestle," from O.It. pistone "a piston," from pestare "to pound," from L.L. pistare, from pistare "to pound."

The distribution of radiation with wavelength for a blackbody, given by → Planck's radiation law.

→ Planck; → distribution.

The earliest Epoch of the Quaternary Period, beginning about 1.6 million years ago and ending 10,000 years ago. Commonly known as the "Ice Age," a time with episodes of widespread continental glaciation.

From Gk. pleisto(s), superlative of Polys "much," cognate with Pers. por, → full, + -cene from Gk. kainos "new, recent."

A → probability function that characterizes → discrete  → random events occurring independently of one another within some definite time or space. It may be regarded as an approximation of the → binomial distribution when the number of events becomes large and the probability of success becomes small. The Poisson distribution is expressed by: f(x) = (λ^xe^-λ)/x!, where λ is the mean number of successes in the interval, e is the base of the → natural logarithm, and x is the number of successes we are interested in.

Named after Siméon Denis Poisson (1781-1840), French mathematician, who developed the application of Fourier series to physical problems and made major contributions to the theory of probability and to the calculus of variations; → distribution.

The angular distance of an object from a celestial pole. It is equal to 90° minus the object's declination.

→ polar; → distance.

A person who studies the structure and theory of government and seeks practical and theoretical solutions to political problems.

→ political; → scientist.

Kârâhikdân, literally "politics scientist," from kârâhik, → politics, + dân "knower," present stem of dânestan, → science.

For a → random variable X, any → distribution which has the form: P(X ≥ x) = (k/x)^α, where x is a value in the range defined for X, k > 0 is a parameter termed location parameter, and α > 0 is the → slope parameter.

→ power; → law; → distribution.

One consequence of the theory of → special relativity, according to which no two events separated by a distance greater than their separation in time multiplied by the → speed of light may have a → causal influence on each other. Violation of this principle leads to → paradoxes, such as that of an → effect preceding its → cause.

→ principle; → relativistic; → causality.

The function that describes the range of possible values that a random variable can attain and the probability that the value of the random variable is within any (measurable) subset of that range.

→ probability; → distribution.

A distance between two nearby events in the frame in which they occur at the same time. It is the distance measured by a ruler at the time of observation. Hence, for a cosmological time t, D_proper = D_C . a(t), where D_C is the → comoving distance, and a(t) is the → scale factor. In the present epoch a = a(t_obs) = 1, and D_proper = D_C.

→ proper; → distance.

The distance derived from the → proper motion of an object. If an object has a known → transverse velocity  u, and has an observed angular motion of dθ/dt, then the proper motion distance is defined as: d = u/(dθ/dt).

→ proper; → motion; → distance

1) A person who tends to view or represent things as they really are; an adherent of → realism.
2) Of or pertaining to realism or to a person who embodies its principles or practices.

→ real; → -ist.

1) Interested in, concerned with, or based on what is real or practical.
2) Philo.: Of or pertaining to realists or → realism.

From → real + -istic, from L. -isticus, Gk. -istikos, from -ikos, → -ic.

The distortion observed in → redshift space of → galaxy clusters caused by peculiar velocities of the members (→ peculiar velocity). In a perfectly homogeneous → Friedmann-Lemaitre Universe the redshifts would accurately measure radial distances from the observer, and the mapping from real space to redshift space would simply be an identity. In an inhomogeneous Universe the peculiar velocities associated with any inhomogeneous structure will introduce a distortion in this mapping (N. Kaiser, 1987, MNRAS 227, 1). See also: → fingers of God, → Kaiser effect.

→ redshift; → space; → distortion;.

The correlation, first established by E. Hubble, between the cosmological recession velocities of galaxies and their distances.

→ redshift; → distance; → relation.

1a) A book in which records of acts, events, names, etc., are kept; a list or → record of such acts, events, etc.
1b) An entry in such a book, record, or list.
1c) → Registration or → registry (Dictionary.com).
1d) In computer science, → registry.
2a) To enter or cause to be entered formally in a register.
2b) To enroll (a student, voter, etc.) in a school or course of study, on the voting rolls, etc. (Dictionary.com).

M.E. registre, from M.Fr., from O.Fr. registre and directly from M.L. registrum, alteration of L.L. regesta "list, matters recorded," noun use of L. regesta, from regestus, p.p. of regerere "to record; retort," literally "to carry back, bring back" from → re- "back" + gerere "carry, bear."

Barnus, from bar- "on, upon, up," → on-, + nus "to write;" cf. Kurd. (Sor.) nus, nusen "to write;" Lori nisane "to write;" variants of nevis-, neveštan, → write.

1) The act or instance of registering.
2) An entry in a register (Dictionary.com).

→ register; → -tion.

1) The act of registering; registration.
2) A place where a register is kept; an office of registration.
3) The state of being registered (Dictionary.com).
4) In → computers, a part of the → central processing unit used to store configuration information about the → software installed on a computer.

→ register + -y.

An adherent or advocate of relativism.

From → relative + -ist a suffix of nouns.

Adj. from → relativism.

1) Physics: Relating to the → relativity theory.
2) Philosophy: Involving or characterized by → relativism.
See also:
→ non-relativistic, → relativistic aberration, → relativistic Doppler effect, → relativistic effect, → relativistic mass, → relativistic particle, → relativistic precession, → relativistic quantum mechanics, → relativistic redshift, → relativistic speed, → relativistic spin precession, → relativistic velocity, → ultrarelativistic, → ultrarelativistic gas.

From → relativist + → -ic.