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

A plot showing the energy emitted by a source as a function of the radiation wavelength or frequency. It is used in many branches of astronomy to characterize astronomical sources, in particular mainly in → near infrared and → middle infrared to study → protostars or → young stellar objects. The SED of these objects is divided in four classes.
Class 0 in which the SED represents a very embedded protostar, where the mass of the central core is small in comparison to the mass of the → accreting envelope. The SED is characterized by the → blackbody radiation of the envelope and peaks at → submillimeter wavelengths.
Class I objects possess a SED that peaks in the → far infrared and is characterized by a weak contribution of the blackbody of the central protostar (detected in near infrared) and the emission of a thick disk and dense envelope. These objects have less mass in the envelope and more massive central cores with respect to Class 0.
Class II objects are the → classical T Tauri stars with a SED due to the emission of a thin disk and the central star. They have accumulated most of their final mass and have dispersed almost completely their circumstellar envelope.
Finally, Class III objects have pure photospheric spectra. Their SED is peaked in the optical and is well approximated by a blackbody emission with a faint → infrared excess due to the presence of a residual optically thin disk that may be the origin of → planetesimals.
This classification scheme can be made more quantitative by defining a → spectral index.

→ spectral; → energy; → distribution.

The → star formation rate as a function of time.

→ star; → formation; → history.

Of, pertaining to, consisting of, or based on → statistics.

Statistic, from → statistics + → -al.

The process of collecting, manipulating, analyzing, and interpreting quantitative data to uncover underlying causes, patterns, and relationships between variables.

→ statistical; → analysis.

A state in which the average density of atoms per cubic centimeter in any atomic state does not change with time and in which, statistically, energy is equally divided among all degrees of freedom if classical concepts prevail.

→ statistical; → equilibrium.

An assumed statement about the way a → random variable is distributed. A statistical hypothesis generally specifies the form of the → probability distribution or the values of the parameters of the distribution. The statement may be true or false. See also → null hypothesis.

→ statistical; → hypothesis.

A method of making decision between rejecting or not rejecting a → null hypothesis on the basis of a set of observations.

→ statistical; → hypothesis; → test.

The process of inferring certain facts about a → statistical population from results found in a → sample.

→ statistical; → inference.

A law that governs the behavior of a system consisting of a large number of particles and which differs from the laws obeyed by each of the particles making up the macroscopic system. See also → dynamical law.

→ statistical; → law.

→ statistical physics.

→ statistical; → mechanics.

The mean parallax of a group of stars that are all at approximately the same distance, as determined from their radial velocities and proper motions.

→ statistical; → parallax.

The branch of physics that applies methods of → probability theory and → statistics to the behavior of large numbers of microscopic particles (such as molecules, atoms, or subatomic particles) in order to explain and predict the overall properties of the system composed of such particles.

→ statistical; → physics.

Any collection of individuals or items from which → samples are drawn. See also → finite population, → infinite population.

→ statistical; → population.

Same as → statistical mechanics.

→ statistical; → thermodynamics.

1) Statistics: A number assigned to each value or range of values of a given quantity, giving the number of times this value or range of values is found to be observed.
2) Statistical mechanics: A multiplicative factor in the expression for the probability of finding a system in a given quantum state. Usually the number of degenerate substates contained in the state.

→ statistical; → weight.

A branch of applied mathematics that deals with the collection and interpretation of quantitative data and the use of probability theory to estimate population parameters.

From Ger. Statistik "political science," from Mod.L. statisticus (collegium) "state affairs," from It. statista "person skilled in statecraft," from stato "state," ultimately from L. status "position, form of government;" cognate with Pers. ist-, istâdan "to stand" (Mid.Pers. êstâtan; O.Pers./Av. sta- "to stand, stand still; set;" Av. hištaiti; cf. Skt. sthâ- "to stand;" Gk. histemi "put, place, weigh," stasis "a standing still;" L. stare "to stand;" Lith. statau "place;" Goth. standan; PIE base *sta- "to stand").

Âmâr "computation, arithmetic; statistics," from âmârdan "to reckon, to calculate," related to ošmârdan, šomârdan, šomordan "to count, to calculate," mar, mâr- "count, reckon, measure," bimar "countless," nahmâr "great, large, big;" Mid.Pers. âmâr "calculating, reckoning;" Av. base mar- "to have in mind, remember, recall," hišmar-; cf. Skt. smr-, smarati "to remember, he remembers," L. memor, memoria, Gk. mermera "care," martyr "witness."

Describing a system or situation for which the → Lorentz factor, γ, is much smaller than 1. See also → ultrarelativistic.

→ ultra- + → relativistic

1a) Of or pertaining to a → syllogism.
1b) Like or consisting of syllogisms.
2a) The part of logic that deals with syllogisms.
2b) Syllogistic reasoning (Dictionary.com).

→ syllogism; → -ic.

A person who believes in → theism.

→ theism; → -ist

A small satellite of → Jupiter, ninth in order from the planet. It is about 8 km in diameter and orbits Jupiter at a mean distance of 7 500 000 km every 130 days. It was discovered in 1975, lost, and then rediscovered in 2000. Also known as Jupiter XVIII.

Named after Themisto, daughter of the river god Inachus, who became the mother of Ister (the river Danube) by Zeus (Jupiter).