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

1a) To or toward what is ahead or in front.
1b) Directed toward a point in advance.
2) To send forward; transmit, especially (a letter or email) to a different address.

From fore "before, in front of," cognate with Pers. farâ, → pro-,+ → -ward.

Piš-su, from piš "forward; in front of; before;" Mid.Pers. pêš, + su, → direction.

Scattering in which photons emerge from the → scattering medium travelling predominantly in the same direction as they entered. The → halos around the Sun and Moon in wet weather are caused by forward scattering by water droplets in the Earth's atmosphere. → backscattering.

→ forward; → scattering.

1) Geology: The process whereby a geologic section (subsurface model of one-, two-, or three dimensions) is transformed into a synthetic seismogram (synthetic seismic record).
2) In → asteroseismology, a model that takes the physical properties of a star as input parameters and predicts the star's oscillations. Then, by finding parameters that yield oscillation frequencies (ω_nlm) close to those observed, one can infer the properties of the observed star. The quantum numbers n, l, and m must be identified before any meaningful comparison between seismic data and model predictions can be made. That mode identification requires a physical interpretation of the measured frequencies.

→ forward; → seismic; → modeling.

A highly → supersonic → shock wave created in a → supernova remnant as the expanding stellar ejecta runs into the → interstellar medium (ISM). This forward shock wave produces sudden, large changes in pressure and temperature behind the shock wave. The forward shock wave also accelerates electrons and other charged particles to extremely high energies. The forward shock front has a velocity of 10⁴ km s^-1 and can heat the shocked gas to temperatures ~ 10⁹ K. While the forward shock continues to expand into the ISM, it creates a → reverse shock that travels back into the freely expanding → supernova ejecta.

→ forward; → shock.

A powerful mathematical tool which is the generalization of the → Fourier series for the analysis of non-periodic functions. The Fourier transform transforms a function defined on physical space into a function defined on the space of frequencies, whose values quantify the "amount" of each periodic frequency contained in the original function. The inverse Fourier transform then reconstructs the original function from its transformed frequency components. The integral F(α) = ∫ f(u)e^-iαudu is called the Fourier transform of F(x) = (1/2π)∫ f(α)e^iαxdx, both integrals from -∞ to + ∞.

→ Fourier analysis; → transform.

Same as the → fundamental interaction.

→ fundamental; → force.

The study dealing with the processes that gave rise to galaxies in a remarkably → early Universe. See also → structure formation, → protogalaxy

→ galaxy; → formation.

The method of relating a measurement in one → reference frame to another moving with a constant velocity with respect to the first within the → Newtonian mechanics. The Galilean transformation between the coordinate systems (x,y,z,t) and (x',y',z',t') is expressed by the relations: x' = x - vt, y' = y, z' = z. Galilean transformations break down at high velocities and for electromagnetic phenomena and is superseded by the → Lorentz transformations.

→ Galilean; → transformation.

A change of the fields of a gauge theory that does not change the value of any measurable quantity.

→ gauge; → transformation.

The total electric flux ψ out of an arbitrary closed surface in free space is equal to the net charge within the surface divided by the → permittivity. In differential form: ∇ . E = ρ/ε₀, where ρ is the → charge density and ε₀ the permittivity. The integral form of the law: ∫E . dS = Q/ε₀ (closed surface integral). This is one of the four → Maxwell's equations.

→ gauss; → law; → electricity.

The → magnetic flux through an arbitrary closed surface equals zero. Mathematically, in differential form: ∇ . B = 0 and in integral form: Φ_B = ∫B.dS = 0 (closed surface integral). This is one of the four → Maxwell's equations. This law expresses the fact that there are no free magnetic poles (→ monopoles) in nature and that all the lines of force of a magnetic field are closed curves.

→ gauss; → law; → magnetism.

In → Lagrangian dynamics, forces related to → generalized coordinates. For any system with n generalized coordinates q_i (i = 1, ..., n), generalized forces are expressed by F_i = ∂L/∂q_i, where L is the → Lagrangian function.

→ generalized; → force.

The process by which dust grains are assembled or produced.

→ grain; → formation.

The weakest of the four fundamental forces of nature. Described by → Newton's law of gravitation and subsequently by Einstein's → general relativity.

→ gravitational; → force.

A reformulation of classical mechanics that predicts the same outcomes as classical mechanics. → Hamiltonian dynamics.

→ Hamiltonian; → mechanics.

The region to the right the → Hayashi track, representing objects that cannot be in → hydrostatic equilibrium. Energy transport in these objects would take place with a → superadiabatic temperature gradient.

→ Hayashi track; → forbidden; → zone.

A cosmological → structure formation model in which the smallest gravitationally bound structures (→ quasars and galaxies) form first, followed by → groups, → galaxy clusters, and → superclusters of galaxies.

→ hierarchical; → structure; → formation.

The meeting of light rays emanating from an object after crossing an optical system.

→ image; → formation.

Relating to → impulse, the force which is very large but acts for a very short time.

Impulsive, adj. of → impulse; → force.

A force arising from the → acceleration of an observer's → frame of reference.

→ inertial; → force.