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

A cosmological model of → structure formation in which larger structures, such as galaxy → superclusters or perhaps even the vast → filaments and → voids, form earlier and then they fragment into smaller structures such as individual galaxies. Opposite of → bottom-up structure formation.

→ top; → down; → structure; → formation.

1) Math.: A mathematical quantity obtained from a given quantity by an algebraic, geometric, or functional transformation.
The transformation itself.
2) To change in form, appearance, or structure; to change in condition, nature, or character; convert.
Physics: To change into another form of energy.
To increase or decrease (the voltage and current characteristics of an alternating-current circuit), as by means of a transformer.
Math.: To change the form of (a figure, expression, etc.) without in general changing the value.

→ trans- + → form.

1) The act or process of transforming. The state of being transformed.
2) The relationship between description of a physical phenomenon in one → reference frame to another. → Galilean transformation; → Lorentz transformation.
3) Math.: The act, process, or result of transforming or mapping.

Verbal noun of → transform.

A device that converts low voltages to higher voltages, or vice versa. A transformer consists of a primary coil and a secondary coil, both traversed by the same magnetic flux.

→ transform + → -or.

The formation of second-generation stars in a → molecular cloud, as set off by the action of → massive stars. → sequential star formation; → radiation-driven implosion.

→ trigger; → star formation.

Without variations; identical, always the same in quality, degree, character, or manner.

→ uni- + → form.

Yekdis, from yek, → uni-, + dis, → form; yeknavâxt, literally "with one rhythm," from yek, → one, + navâxt "rhythm," from navâxtan, navâzidan "to play an instrument; to gratify," navâ "music, song, melody" (Mid.Pers. nw'c "to treat kindly, honour," niwag "music, melody;" Proto-Iranian *ni-uac-, from ni- "down; into," → ni- (PIE), + *uac- "to speak, treat kindly").

The motion of an object around a fixed point at a constant angular speed, and at constant radius.

→ uniform; → circular; → motion.

A field that at a given instant has the same value at all points within a specified region of interest.

→ uniform; field.

A → magnetic field whose direction does not change and whose strength is constant at every point.

→ uniform; → magnetic; → field.

Motion at a constant → velocity. The state of rest is a special case of uniform motion. → accelerated motion; → inertial motion.

→ uniform; motion.

1) Of, characterized by, or conforming to → uniformity.
2) Of or relating to → uniformitarianism.

→ uniformity + -arian.

The doctrine whereby geologic processes (→ erosion, → deposition, → compaction, and → uplift) observed at Earth's surface now are the same that have shaped Earth's landscape over long periods of time in the past. The term uniformitarianism was first used in 1832 by William Whewell, to present an alternative explanation for the origin of the Earth. The prevailing view at that time was that the Earth was created through supernatural means and had been affected by a series of catastrophic events such as the biblical Flood. This theory is called → catastrophism. The ideas behind uniformitarianism originated with the work of Scottish geologist James Hutton. In 1785, Hutton presented at the meetings of the Royal Society of Edinburgh that the Earth had a long history and that this history could be interpreted in terms of processes currently observed. For example, he suggested that deep soil profiles were formed by the weathering of bedrock over thousands of years. He also suggested that supernatural theories were not needed to explain the geologic history of the Earth (PhysicalGeography.net).

→ uniformitarian; → -ism.

The state or quality of being uniform.

→ uniform; → -ity.

A transformation whose reciprocal is equal to its Hermitian conjugate.

→ unitary; → transformation.

A weak attractive force between neutral atoms and molecules arising from polarization induced in each particle by the presence of other particles. All molecules contain electrically charged particles, and even though the molecule as a whole is electrically neutral there do exist between molecules van der Waals attractive forces of electric origin.

Named after Dutch physicist Johannes Diderik van der Waals (1837-1923), Nobel Prize in Physics 1910; → force.

The concept of star formation pertaining to a variety of systems (OB associations, giant H II regions, H II galaxies, massive star clusters, etc.) that are believed to have formed large numbers of stars in a very short time.

→ violent; → star formation.

The force per unit volume or per unit mass arising from the action of tangential stresses in a moving → viscous fluid.

→ viscous; → force.

A graphical representation of the shape of a wave for a given instant in time.

→ wave; → form.

The resolution of a complex waveform into a sum of simple periodic waves, usually by computer means.

→ waveform; → analysis.

Same as → weak interaction.

→ weak; → force.