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

1) The process of inducing or creating a state of → activity.
2) The process of producing a → radioactive isotope by bombarding a → stable → nuclide with → nuclear particles (such as → protons, → neutrons, → alpha particles, heavy ions, etc.).

Verbal noun of → activate; → -tion.

Chemistry: The minimum amount of energy that is required to activate → atoms or → molecules to a condition in which they can undergo a → chemical reaction. Most reactions involving neutral molecules cannot take place at all until they have acquired the energy needed to stretch, bend, or otherwise distort one or more → bonds. In most cases, the activation energy is supplied by → thermal energy.

→ activation; → energy.

1) Being in a state of action; not quiescent.
2) Functioning or capable of functioning.
3) Marked by vigorous activity.

M.Fr. actif, from L. activus, from actus, p.p. of agere, → act.

Žirâ, adj. from stem žir, → act + suffix -â.

A central region of an → active galaxy, which is a → light-year or less in diameter and has an abnormally high luminosity. The nucleus emits high energy radiation (→ gamma rays, → X-rays, → ultraviolet) and shows → variability over various time-scales, sometimes very short (hours to weeks). Emission line spectra reveal high velocity motions up to 10⁴ km s^-1. AGNs are divided into two main types. Type I refers to an AGN whose nucleus is visible (the spectra has both narrow and broad emission lines), while in type II AGN, the broad line region (BLR) is obscured and the lines are very narrow. This may be due either to the viewing angle or some intrinsic difference in structure. See also → broad-line region, → narrow-line region, → quasar.

→ active; → galactic; → nucleus.

A galaxy that produces huge amounts of energy at its center, which cannot be attributed to normal processes from stars, interstellar medium, and their interactions. There are several types of active galaxies: → Seyfert galaxies, → quasars, and → blazars. All of these objects show brightness variations, some as short as 3 hours. These fluctuations indicate a relatively very small size for the central object, because an object cannot vary in brightness faster than light can travel across it. For example, an object that is one → light-year in diameter cannot vary significantly in brightness over a period of less than one year.

→ active; → galaxy.

A technique for improving the → resolving power of a telescope by controlling the shape of the main mirror at a relatively slow rate. The → image quality is optimized automatically through constant adjustments by in-built corrective → actuators operating at fairly low temporal frequency ~0.05 Hz or less. → adaptive optics.

→ active; → optics.

A solar → prominence with very rapid motion (up to 2,000 km s^-1), moving and changing in appearance over a few minutes of time, in contrast to a → quiescent prominence.

→ active; → prominence.

An area of the Sun exhibiting → solar activity with the presence of → sunspots, → flares, → faculae, → prominences, and other phenomena associated with intense magnetic fields.

→ active; → region.

The Sun during its 11-year cycle of activity when spots, flares, prominences, and variations in radiofrequency radiation are at a maximum.

→ active; → sun.

1) The doctrine or practice of vigorous action or involvement as a means of achieving political or other goals, sometimes by demonstrations, protests, etc. (Dictionary.com). See also → activist.
2) Philosophy: a) A theory that the essence of reality is pure activity, especially spiritual activity, or process. b) A theory that the relationship between the mind and the objects of perception depends upon the action of the mind (Dictionary.com).

→ active; → action; → -ism.

An especially active, vigorous advocate of a cause, especially a political cause (Dictionary.com).

Agent noun from → activism.

For a radioactive substance, the average number of atoms disintegrating per unit time.

Activity, from → active + -ity.

Žirandegi, noun from žirandé, → active.

1) One who takes part; a participant.
2) A theatrical performer.

→ act + → -or.

1) Existing in act or fact; real.
2) Philosophy: The character of what is realized in act (such as a statue), as opposed to what can potentially be realized (from a piece of rock).

M.E. actuel, from O.Fr. actuel "now existing, up to date," from L. actualis "active, pertaining to action," adj. form of actus, → act.

Žirvand, from žir, → act, + -vand a suffix forming adjectives denoting "possessed of, similarity, relation," variants -âvand, -van (e.g. xodâvand "possessor, master," pulâdvand "hard as steel, name of a hero," dowlatvand "rich," setarvan "mule-like, barren," polvan "bridge-like, a raised path"), from Mid.Pers. -âwand (hunarâwand "skilled," warzâwand "powerful"); Av. -vant (aurvant- "swift," surunvant- "audible"); cf. Skt. -vant (amavant- "having attacking power").

1) The quality or state of being actual or something that is actual; reality.
2) Philosophy: According to Aristotle, what has → form and can causally interact with other things, as opposed to → potentiality.

→ actual; → -ity.

The act or process of actualizing.

Verbal noun of → actualize; → -tion.

To make actual or real; turn into action or fact.

→ actual; → -ize.

1) To put into mechanical action or motion.
2) To incite or move to action; motivate.

From L. actuatus, p.p. of actuare, from actus, → act.

Baržiridan, from bar- "on, upon, up," → on-, + žiridan "to → act."

The act or process of putting into action; activation.

Verbal noun of → actuate.

A mechanism to activate process control equipment by use of pneumatic, hydraulic, or electronic signals.

→ actuate; → -or.