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

In a wave train, a correlation between the phases of waves at points separated in space at a given time.

→ spatial; → coherence.

The smallest detail that can be seen in an image. Same as → angular resolution.

→ spatial; → resolution.

A period of low → solar activity that lasted from about A.D. 1420 to 1570. It occurred before → sunspots had been studied, and was discovered by analysis of the proportion of carbon-14 in tree rings, which is strongly correlated with solar activity.

Named for the German astronomer Gustav Spörer (1822-1895); → minimum.

The empirical law that predicts the variation of → sunspot latitudes during a → solar cycle. At the start of a sunspot cycle, sunspots tend to appear around 30° to 45° latitude on the Sun's surface. As the cycle progresses, they appear at lower and lower latitudes, until 5° to 10°, at the end of the cycle. This tendency is revealed on a → butterfly diagram. Although named after Gustav Spörer, the "law" was first discovered by Richard Carrington.

→ Sporer minimum; → law.

To utter words with the ordinary voice (not singing) to communicate; to talk.

From M.E. speken "to speak," from O.E. specan, alteration of earlier sprecan "to speak;" cf. Low Germ. spreken "to speak," Du. spreken, Ger. sprechen "to speak;" ultimately from PIE *spreg- "to make a sound, utter, speak."

From M.P. saxwanitan "to speak, to talk," → speech.

Of a distinct or particular kind or character; having a particular function or purpose; not common, usual, or general.

M.E., from O.Fr. especial, from L. specialis "individual, particular," from → species "appearance, kind, sort."

Vižé, from Mid.Pers. apēcak "pure, sacred," from *apa-vēcak "set apart," from prefix apa- + vēcak, from vēxtan (Mod.Pers. bixtan) "to detach, separate, sift, remove," Av. vaēk- "to select, sort out, sift," pr. vaēca-, Skt. vic-, vinakti "to sift, winnow, separate; to inquire."

Of, relating to, or subject to the theory of → special relativity.

→ special; → relativistic.

The theory formulated by A. Einstein in 1905, which is based on the following two → postulates:
1) → Principle of relativity: The laws of physical phenomena are the same when studied in terms of two reference systems moving at a constant velocity relative to each other.
2) → Principle of constancy: The → velocity of light in free space is the same for all observers and is independent of the relative velocity of the source of light and the observer.
The term "special theory of relativity" refers to the restriction in the first postulate to reference systems moving at a constant velocity relative to each other (→ inertial reference frame). See also → general relativity.

→ special; → relativity.

1) A class of individuals having some common characteristics or qualities; distinct sort or kind.
2) Biology: The major subdivision of a genus or subgenus, regarded as the basic category of biological classification, composed of related individuals that resemble one another, are able to breed among themselves, but are not able to breed with members of another species.
3) Logic: One of the classes of things included with other classes in a genus. The set of things within one of these classes (Dictionary.com).

From L. species "a particular sort, kind, or type," originally "a sight, look, view, appearance," from specere "to look at, to see, behold;" PIE root spek- "to look around," → scope.

Âraz, from intensive/nuance â- + raz-, from Av. razan "order, → rule," from rāz- "to put in line, direct set," cf. Mod.Pers. raj "line, row," variants raž, rak, râk, rezg (Lori), radé, râdé "line, rule, row," rasté, râsté "row, a market with regular ranges of shops;" ris, risé "straight;" → right.

1) Clearly defined or identified; precise; particular.
2) Belonging or relating uniquely to a particular subject; not general.
3) Biology: Relating to species or a species.
4) Physics: Of or denoting a physical quantity expressed in terms of a unit mass, volume, or other measure, in order to give a value independent of the properties or scale of the particular system studied. → specific angular momentum; → specific charge; → specific density; → specific gravity; → specific heat; → specific humidity; → specific intensity; → specific volume.

From Fr. spécifique and directly from L.L. specificus "constituting a kind or sort," from L. species "kind, sort," → species.

Âbizé, from Mid.Pers. apēcak "pure, sacred" (older form of vižé, → special), from *apa-vēcak "set apart," from prefix apa- + vēcak, from vēxtan (Mod.Pers. bixtan) "to detach, separate, sift, remove," Av. vaēk- "to select, sort out, sift," pr. vaēca-, Skt. vic-, vinakti "to sift, winnow, separate; to inquire."

→ Angular momentum per unit mass.

→ specific; → angular; → momentum.

The electric charge to mass ratio of an elementary particle.

→ specific; → charge.

Same as → relative density.

→ specific; → density.

The ratio of the density of a substance at the temperature under consideration to the density of water at the temperature of its maximum density (4 °C).

→ specific; → gravity.

1) The quantity of heat required to raise the temperature of 1 gm of a substance through 1 °C. More generally, the → heat capacity of a unit mass of a substance. For a homogeneous body it is expressed as: C = dQ/M dT, where dQ is the quantity of heat transferred to a mass of M to raise the temperature by dT. It is often convenient to use the gram-mole as a unit of mass, → molar heat capacity.
2) For a gas there are two principal specific heats depending on the way in which the temperature is increased: i) that measured at constant pressure, C_P, and ii) that measured at constant volume, C_V. The specific heat C_P is greater than C_V, because a gas heated at constant pressure expands, and heat energy must be supplied equivalent to the work done in the expansion. The ratio γ = C_P/C_V is called the → adiabatic index. It varies from 1.66 for mono-atomic gases to a little over 1 for gases with complex molecules.

→ specific; → heat.

The dimensionless ratio of the mass of water vapor to the total mass in a particular volume. → humidity

→ specific; → humidity.

A measure of the amount of radiation received per unit solid angle per unit time per unit area normally from an element of surface.

→ specific; → intensity.

Star formation rate per unit → mass. More specifically, the → star formation rate in a galaxy divided by the → stellar mass of the galaxy. Observations of galaxies over a wide range of → redshifts suggest that the slope of the SFR-M_* relation is about unity, which implies that their sSFR does not depend strongly on stellar mass. Specific star formation rates increase out to z ~ 2 and are constant, or perhaps slowly increasing, from z = 2 out to z = 6, though with a large scatter, sSFR ~ 2-10 Gyr^-1 (Lehnert et al., 2015, A&A 577, A112, and references therein).

→ specific; → star; → formation; → rate.

The volume occupied by unit mass of a substance. Specific volume is the reciprocal of density.

→ specific; → volume.

1) The act of specifying.
2) A particular item, aspect, calculation, etc., in such a description.
3) Something specified, as in a bill of particulars; a specified particular, item, or article (Dictionary.com).

Verbal noun of → specify.