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blueshift

Overview page. Subjects: Astronomy and Astrophysics — Chemistry.

A Doppler shift of light towards the blue end of the spectrum, caused when the emitting source is approaching the observer. See also Radial Velocity; Redshift.

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Boltzmann constant

Overview page. Subjects: Chemistry — Astronomy and Astrophysics.

Symbol k. The ratio of the universal gas constant (R) to the Avogadro constant (N A). It may be thought of therefore as the gas constant per molecule:k = R/N A =...

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Cerenkov counter

Overview page. Subjects: Chemistry — Astronomy and Astrophysics.

A device for detecting high-energy charged particles via the Cerenkov radiation they generate. This radiation, which appears as a predominantly bluish light, can be detected using...

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Cerenkov radiation

Overview page. Subjects: Chemistry — Astronomy and Astrophysics.

The light emitted by charged particles such as protons or electrons when they pass through a transparent medium (e.g. the Earth's atmosphere, glass, or certain plastics) at a speed greater...

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correlation function

Overview page. Subjects: Astronomy and Astrophysics — Chemistry.

A mathematical function used in the statistical description of galaxy clustering. It measures the excess probability of finding a galaxy at a given distance from a particular galaxy,...

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degeneracy

Overview page. Subjects: Astronomy and Astrophysics — Chemistry.

A state of matter attained when atomic particles are packed together as tightly as is physically possible, at densities of several thousand tonnes per cubic metre. Particles which are very...

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docking

Overview page. Subjects: Chemistry — Astronomy and Astrophysics.

The binding of any macromolecule or part of such a molecule to its specific harbouring site on another molecular structure. See also signal recognition particle receptor.

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doublet

Overview page. Subjects: Astronomy and Astrophysics — Chemistry.

A pair of associated lines in certain spectra, e.g. the two lines that make up the sodium D-lines.

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electron density

Overview page. Subjects: Chemistry — Astronomy and Astrophysics.

The number of free electrons per unit volume of space. Typical values range from less than 10−4 electrons/cm3 in intergalactic space to 0.03 electrons/cm3 in the disk of our Galaxy, 104 ele...

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Faraday effect

Overview page. Subjects: Astronomy and Astrophysics — Chemistry.

The rotation of the plane of polarization of an electromagnetic wave as it passes through a region containing free electrons and a magnetic field; also known as Faraday rotation. The amount...

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fine structure

Overview page. Subjects: Astronomy and Astrophysics — Chemistry.

Closely spaced spectral lines arising from transitions between energy levels that are split by the vibrational or rotational motion of a molecule or by electron spin. They are visible only...

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flux density

Overview page. Subjects: Astronomy and Astrophysics — Chemistry.

1 (S) Spectral flux density, a quantity that indicates the observed strength of an astronomical source. It is a measure of the radiant power passing through unit area in unit...

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f-number

Overview page. Subjects: Chemistry — Astronomy and Astrophysics.

The number obtained by dividing the focal length of a lens or mirror by its diameter; it is the same as the focal ratio.

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forward scattering

Overview page. Subjects: Astronomy and Astrophysics — Chemistry.

Scattering in which photons emerge from the scattering medium travelling predominantly in the same direction as they entered. Forward scattering and backscattering always occur together,...

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Grotrian diagram

Overview page. Subjects: Chemistry — Astronomy and Astrophysics.

A diagram that summarizes the energy levels and the allowed transitions between these energy levels in an atom. The energy is plotted vertically with a horizontal line for each energy...

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Humphreys series

Overview page. Subjects: Astronomy and Astrophysics — Chemistry.

A series of lines in the hydrogen spectrum with the form 1/λ=R(1/62 – 1/n 2), n=7,8,9…, where λ is the wavelength associated with the lines and R is the Rydberg constant. The...

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hydrogen ion

Overview page. Subjects: Chemistry — Astronomy and Astrophysics.

A hydrogen atom that has gained or lost an electron, and thus has an electric charge. The positive hydrogen ion, H+, has lost its only electron and therefore consists of a single proton. A...

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hyperfine structure

Overview page. Subjects: Astronomy and Astrophysics — Chemistry.

Very close splitting of spectral lines, due to interaction between the spin of the atomic nucleus and the spin of an orbiting electron. It is a much smaller effect than fine structure and...

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interference filter

Overview page. Subjects: Astronomy and Astrophysics — Chemistry.

A type of filter that uses the effect of interference of light to limit the wavelengths that pass through it. Ordinary filters are coloured, but interference filters consist of very thin...

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interferometer

Overview page. Subjects: Astronomy and Astrophysics — Chemistry.

An instrument used in remote sensing that forms and uses interference patterns in radiation to measure the wavelengths of that radiation.

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