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

A number that represents a → charge-coupled device (CCD)'s output and is proportional to the → electron charge created by the → photons, plus the constant → bias offset. The relationship between the ADUs generated and the number of electrons acquired on the CCD is defined by the → CCD gain. Intensities given in ADUs provide a convenient method for comparing images and data generated by different cameras. Also referred to as → count and digital number. In most cases, the analog signal is digitalized by an analog-to-digital (A/D) converter and fed into a computer where further manipulation and analysis are done on what the detector originally produced from the star's photons (Howell, S.B., Handbook of CCD Astronomy, Cambridge Univ. Press, 2000).

→ analogue; → digital; → unit.

Unit of length used to describe wavelengths and interatomic distances. 1 Å = 10^-10 m.

Named after Anders Jonas Ångström, Swedish physicist and astronomer who founded the science of spectroscopy and discovered by studying the solar spectrum that there is hydrogen in the Sun's atmosphere; → unit.

1) A unit of length equal to 149 597 870 700 m exactly, with symbol "au" (re-definition at the International Astronomical Union's 28th General Assembly in Beijing, China, August 20-31). The astronomical unit equals 1.5813 × 10^-5 → light-years and 4.8481 ×10^-6 → parsecs.
2) Previous definition: The radius of a circular orbit in which a body of negligible mass, and free of perturbations, would revolve around the Sun in 2 π / k days, where k is the → Gaussian gravitational constant. This is slightly less than the semi-major axis of the Earth's orbit.

→ astronomical; → unit.

A unit of mass used for atoms and molecules, equal to 1/12 of the mass of an atom of carbon-12 (including orbital electrons). It is equal to 1.660 33 × 10^-24 g.

→ atomic; → mass; → unit.

The primary component of a → computer that processes instructions. It runs the → operating system and → applications, constantly receiving input from the user or active → software programs. The CPU has two typical components: 1) Control Unit, which extracts instructions from memory and decodes and executes them. 2) Arithmetic Logic Unit (ALU), which handles arithmetic and logical operations.

→ central; → processing; → unit.

A → metric system of physical units based on → centimeter (length), → gram (mass), and → second (time).

CGS, the initials of → centimeter, → gram, and → second; meter, kilogram, and second; → unit.

A member of a communistic community; an advocate of such a community.

→ community; → -ary; → -an.

A doctrine or system of social organization that upholds the importance of communities. It tends to lessen the focus on individual rights and increase the focus on communal responsibilities.

→ communitarian; → -ism.

Of or relating to a community; communal.

→ community; → -ary.

1a) A social group whose members share common characteristics or interests, such as values, identity, and often a common location (e.g. a village, town, or neighborhood).
1b) Ecology: A group of populations of different species (plants and animals) within a specified location in space and time. 2) Common ownership or participation; joint possession.

Ultimately from L. communitas "partnership, society, fellowship," from communis, → common "common, public, general," + -itas, → -ity

Hamdârgân, from hamdâr, → common, + -gân suffix forming plural entities, from Mid.Pers. -gânag, -gâna, on the model of hamegân, → public.

The unit of electric charge in the → cgs system of units. Also called the → statcoulomb. The esu is defined such that if two objects, each carrying a charge of +1 esu, are 1 cm aparat, then they repel each other with a force of 1 → dyne. 1 esu = 3.3356 × 10^-10 → coulombs.

→ electrostatic; → unit; → charge.

In radio astronomy, same as → jansky (symbol Jy), a unit of electromagnetic flux equivalent to 10^-26 watts per square meter per Hertz.

→ flux; → density.

The metric system of units based on the → meter, → kilogram, → second, → ampere, → kelvin, and → candela. Also called MSKA system. Other SI units are → hertz, → radian, → newton, → joule, → watt, → coulomb, → volt, → ohm, → farad, → weber, and → tesla.

→ international; → system; → unit.

A physical → measurement unit in the → metric system.

→ metric; → unit.

The international system of units based on the → meter, → kilogram, and → second.

MKS, the initials of → meter, → kilogram, and → second; meter, kilogram, and second; → unit.

Physical units of measurement defined in terms of universal physical constants in such a manner that some chosen physical constants (e.g. the speed of light, Planck's constant, Boltzmann's constant, etc.) are equal to unity. The use of natural units allows these constants to be omitted from mathematical equations, leading to simpler calculations.

→ natural; → unit.

1) An appropriate or favorable time or → occasion.
2) A situation or condition favorable for attainment of a goal (Dictionary.com).

→ opportune + → -ity.

A set of → natural units in which the normalized units are: the gravitational constant, Planck's constant, the speed of light, the Coulomb constant, and Boltzmann's constant.

→ Planck; → unit.

A property in → quantum mechanics whereby in a quantum system the sum of all probabilities of all possible outcomes must be 1. Quantum unitarity makes the modulous of a → quantum state invariant with time.

→ quantum. → unitary.

One of the units into which an aggregate is divided for the purpose of sampling, each unit being regarded as individual and indivisible when the selection is made.

→ sampling; → unit.