An Etymological Dictionary of Astronomy and Astrophysics
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The mathematical description of the interval (→ space-time separation) between → events ("points" in space-time) in a → homogeneous and → isotropic → Universe. It results from an exact solution of → Einstein's field equations of → general relativity. Under the assumptions, the Robertson-Walker interval is expressed by:
ds² = c²dt² - R²(t) [dr²/(1 - kr²) + r²dθ² + r²sin²θ dθ²)].
Same as Friedmann-Lemaître-Robertson-Walker metric. Compare → Minkowski metric.

Named after Howard Percy Robertson (1903-1961), American mathematician and physicist, and Arthur Geoffrey Walker (1909-2001), British mathematician and physicist, for their contributions to physics and physical cosmology; → metric.

In → general relativity, the → metric that describes the → space-time outside a static mass with spherically symmetric distribution.

→ Schwarzschild black hole; → metric.

A tensor that is the negative of its → transpose. For example, a second-order covariant tensor A_jk if its components satisfy the equality: A_jk = - A_kj. Also called antisymmetric tensor.

→ skew; → symmetric; → tensor.

Tânsor, → tensor; pâd-, → anti-; hamâmun, → symmetric.

The → extreme adaptive optics system and → coronagraphic facility at the → European Southern Observatory (ESO) → Very Large Telescope (VLT) (UT3) available from May 2014. Its primary science goal is imaging, low-resolution spectroscopic, and polarimetric characterization of → exoplanetary system at → visible and → near-infrared wavelengths (0.5-2.32 μm). SPHERE is capable of obtaining → diffraction-limited images at 0''.02 to 0''.08 resolution depending on the wavelength. Its → spectral resolution is 30 to 350, depending on the mode.

→ spectro-; → polarimetric; → high; → contrast; → exoplanet.

Of or relating to → spectrophotometry.

→ spectrum; → photometry.

Of or relating to → spectropolarimetry.

→ spectropolarimetry; → -ic.

1) Of or pertaining to → stoichiometry.
2) Pertaining to or involving substances that are in the exact proportions required for a given reaction.

→ stoichiometry; → -ic.

A relation between two quantities such that the first is to the second as the second is to the first. In symbols: a R b = b R a. For example, multiplication is an operation with a symmetric relation between the factors: 5 x 3 = 3 x 5.

→ symmetric; → relation.

A tensor that is → invariant under any → permutation of its indices (→ index). In other words, a tensor that equals its → transpose. For example, a second-order → covariant tensor A_jk if its components satisfy the equality: A_jk = A_kj.

→ symmetric; → tensor.

Characterized by or exhibiting → symmetry.

Adj. of → symmetry.

Relating to or used in → trigonometry. → trigonometric function.

→ trigonometry; → -ic.

A function of an angle, one of six functions (sine, cosine, tangent, cotangent, secant, and cosecant) that represent ratios of sides of right triangles. Also called circular function.

→ trigonometric; → function.

The → parallax of a nearby star (less than 300 → light-years) against the background of more distant stars resulting from the motion of the Earth in its orbit around the Sun.

→ trigonometric; → parallax.