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

A lens placed at or near the focal plane of a telescope to create an image of the primary mirror inside the instrument.

→ field; → lens.

An → O-type star which is apparently not associated with a → star cluster. A significant fraction of → massive stars in the → Milky Way and other galaxies are located far from star clusters and → star-forming regions. It is known that some of these stars are → runaways, i.e. possess high → space velocities (determined through the → proper motion and/or → radial velocity measurements), and therefore most likely were formed in embedded clusters and then ejected into the field because of dynamical interactions or → binary-→ supernova explosions. However, there exists a group of field O stars whose runaway status is difficult to prove via direct proper motion measurements or whose low space velocities and/or young ages appear to be incompatible with their large separation from known star clusters. The existence of this group led some authors to believe that these stars can form → in situ. The question of whether or not O stars can form in isolation (→ isolated massive star formation) is of crucial importance for → star formation models (Gvaramadze et al., 2012, MNRAS, 424, 3037).

→ field; → O star.

An astronomical object that is seen in the direction of a group but not physically belonging to the group. → field galaxy.

→ field; → object.

The region of → space surrounding a body, such as a mass of → matter, a → charged particle, or a → magnet, within which it can exert a → force on another similar body not in contact with it.

→ field; → force.

The entire angular expanse of the sky viewed by an optical instrument.

→ field; → view.

The effect of the Earth's rotation on the position of the image formed on the → focal plane of a telescope during long exposures. In the case of → equatorial mounting, the image remains fixed, whereas it turns continuously with an → altazimuth mounting. In the latter case the image motion must be compensated by an appropriate mechanism, → field rotator.

→ field; → rotation.

A device used on a telescope to correct for the → field rotation while tracking an object.

→ field; → rotator.

A star that does not belong to a stellar cluster, but happens to be adjacent to it.

→ field; → star.

A diaphragm located at an image plane of an optical system that determines the size and shape of the image. → aperture stop.

→ field; → stop.

1) A theory which uses the concept of → field to describe physical phenomena. It consists of two types: → classical field theory and → quantum field theory.
2) Math.: A branch of mathematics which studies the → fields.

→ field; → theory.

Exposure of a diffuse and uniform source in order to calibrate the non-uniformity of an imaging detector such as a CCD.

→ flat; → field.

Meydân, → field; taxt, → flat.

Same as → field of force.

→ force; → field.

The condition in a plasma when the → Lorentz force is zero, that is when the electric current flows along the magnetic field. Force-free magnetic fields are encountered in astrophysical plasmas with negligible gas pressure. The solar corona is the best available example of such fields in action in a plasma.

→ force; → free; → magnetic; → field.

In a physical system, the → magnetic field belonging to an earlier magnetic process or event. A fossil magnetic field may be a vanished one or exist in relic forms. As an example, the solar magnetic field, which was present during the formation of the Sun, has disappeared over the last 4.6 billions years.

→ fossil;→ magnetic; → field;

An observing project using the → Hubble Space Telescope (HST) and the → Spitzer Space Telescope to obtain deep images for cosmological studies. The Frontier Fields combines the power of HST and Spitzer with the natural gravitational telescopes of massive high-magnification clusters of galaxies to produce the deepest observations of clusters and their lensed galaxies ever obtained. Six clusters (Abell 2744, MACSJ0416.1-2403, MACSJ0717.5+3745, MACSJ1149.5+2223, Abell S1063, and Abell 370) were selected based on their lensing strength, sky darkness, Galactic extinction, parallel field suitability, accessibility to ground-based facilities, HST, Spitzer and JWST observability, and preexisting ancillary data. (Lotz et al., 2016, arxiv/1605.06567 and references therein).

→ frontier; → field.

A → magnetic field line in a → fluid when the motion of the fluid carries the magnetic field along with it.

Frozen, p.p. of → freeze; → magnetic; → line.

The magnetic field that is generated within the Earth and extends out around the Earth. The intensity of the magnetic field at the Earth's surface is about 0.32 → gauss at the equator and 0.62 gauss at the north pole.

→ geomagnetic; → field.

The region of space in which → gravitational attraction exists.

→ gravitational; → field.

A theory that treats gravity as a field rather than a force acting at a distance.

→ gravitational; → field.

A unit used to express the strength of average → far ultraviolet (FUV) intensity in the → interstellar radiation field. It is equal to 1.2 × 10^-4 erg cm^-2 s^-1 sr^-1 = 1.6 × 10^-3 cm^-2 s^-1 = 10⁸ photons cm^-2 s^-1.

Named after Harm Habing, a pioneer in this field (Habing, H. J., 1968, Bull. Astr. Netherlands 19, 421).