An Etymological Dictionary of Astronomy and Astrophysics
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Any of a set of physical properties whose values determine the characteristics or behavior of a system; for example, → mass, → size, → temperature, → luminosity, etc.

→ physical; → parameter.

An instrument for measuring electrical quantities by balancing an unknown potential difference against a known potential difference.

From potenti(al), → potential + -o + → -meter.

General term for the class of → actinometers that measure the intensity of solar radiation received on the surface of the Earth. It functions by converting the heat of the sunlight into a voltage using a device called a thermopile, and a recording voltmeter.

From pyr-, from → pyro- + → heliometer.

A device used for measuring high temperatures. By comparing a source whose temperature is to be measured to a standardized source of illumination, it determines the temperature of the former source.

→ pyro- + → -meter.

An → interferometer designed for radio frequencies.

→ radio; → interferometer.

An instrument that measures the intensity of radiant energy.

→ radio; → -meter.

A dimensionless quantity characterizing the → interstellar extinction, defined by the total-to-selective extinction ratio: R_V = A_V/E(B-V). The typical value found for the reddening parameter in the Milky Way is R_V ~ 3.1, but it is known to vary from one line of sight to another, from values as 2 to as large as 6. Very large → dust grains would produce extinction with R_V → ∞.

→ reddening; → parameter.

The northward variation of the Coriolis parameter, arising from the sphericity of the Earth.

→ Rossby number; → parameter.

The angle at the observer subtended by the equatorial radius of the Sun, Moon, or a planet.

→ semi-; → diameter.

A quantity that defines the type of → scattering.

→ size; → parameter.

In a → power-law distribution or → regression, the → exponent that represents the effect of the → independent variable, x, on the → dependent variable, y. X has no association with y if the slope parameter = 0 and x has strong association with y if the slope parameter is large.

→ slope; → parameter.

1) A spectrograph in which the spectrum is recorded by electronic means so that wavelength, intensity, etc. can be measured.
2) An instrument for determining the distribution of energies in a beam of particles.

→ spectro-; → -meter.

An instrument designed to measure the intensity of a particular spectral line or a series of spectral lines.

→ spectro-; → photometer.

An international project to construct a highly sensitive radio interferometer array operating between 0.15 and 20 GHz with an effective collecting area of one square kilometer. The number of individual telescopes will be 2000 to 3000. SKA will have a sensitivity 100 times higher than that of today's best radio telescopes and an angular resolution < 0.1 arcsec at 1.4 GHz. The site will be selected in 2012 and early science with Phase 1 is scheduled for from 2016 on. See also the SKA homepage.

→ square; → kilometer; → array.

Four parameters which are needed to fully describe the → polarization state of → electromagnetic radiation. They involve the maximum and minimum intensity, the ellipticity, and the direction of polarization. The four Stokes parameters are traditionally defined as follows:
I ≡ total intensity.
Q ≡ I₀ - I₉₀ = difference in intensities between → horizontal and → vertical  → linearly polarized components.
U ≡ I₊₄₅ - I_-45 = difference in intensities between linearly polarized components oriented at +45° and -45° (or 135°).
V ≡ I_rcp - I_lcp = difference in intensities between right and left → circularly polarized polarized components.

→ Stokes; → parameter.

Of or pertaining to scales smaller than millimeter.

→ sub-; → millimeter.

The study of astronomical objects with → submillimeter waves. As with millimeter-wave astronomy, this part of the spectrum is rich in lines emitted by interstellar molecules and dust.

→ submillimeter; → astronomy.

A member of an extremely luminous population of → high-redshift galaxies which are detected in → submillimeter waves (→ flux density at 850 μm ≥ 3 - 5 mJy). SMGs are powered primarily by star formation rather than an → active galactic nucleus (AGN). Because of their high → dust content, these galaxies emit almost all of their luminosity in the infrared, with a → bolometric luminosity ranging from 10¹²-10¹³ → solar luminosities. As such, SMGs resemble → ultraluminous infrared galaxies (ULIRGs), which are almost exclusively → merging galaxies. Indeed, many observations support a → merger origin for SMGs (see, e.g. C.C. Hayward et al. 2011 and references therein, astro-ph/1101.0002).

→ submillimeter; → galaxy.

That part of the → electromagnetic radiation with a → wavelength beyond 300 → microns.

→ submillimeter; → radiation.

An electromagnetic wave having wavelengths less than one millimeter (frequencies greater than 300 gigahertz).

→ millimeter; → wave.