An Etymological Dictionary of Astronomy and Astrophysics
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In Saturn's rings, the gap between rings B and C.

Named after Bernard Lyot (1897-1952), French astronomer who discovered the division. He was also a distinguished solar observer and invented (1930) the → coronagraph; → division.

The cone that confines the pressure disturbance created by a → supersonic object moving in a → compressible medium.

→ Mach number; → cone.

A stellar → explosion with energies between those of a → nova and a → supernova and observationally distinguished by being brighter than a typical nova (M_V ~ -8 mag) but fainter than a typical supernova (M_V ~ -19 mag) (Kulkarni 2005; arXiv:astro-ph/0510256).

→ macro-; → nova.

The transport of the magnetic field by a fluid. It is given by the term ∇ x (v x B) in the → induction equation.

→ magnetic; → advection.

Of magnetic field lines, the condition for them to be connected or the process whereby they become connected or connective.

→ magnetic;→ connectivity.

A physical constant relating mechanical and electromagnetic units of measurement. It has the value of 4π × 10^-7 henry per meter. Also called the permeability of free space, or → absolute permeability.

→ magnetic; → constant.

Thermal → convection modified by the presence of magnetic fields.

→ magnetic; → convection.

In terrestrial magnetism, the difference between → true north (the axis around which the earth rotates) and magnetic north (the direction the needle of a compass will point,→ magnetic pole).

→ magnetic; → declination.

The process whereby the magnetic field tends to diffuse across the plasma and to smooth out any local inhomogeneities under the influence of a finite resistance in the plasma. For a stationary plasma the → induction equation becomes a pure → diffusion equation: ∂B/∂t = D_m∇²B, where D_m = (μ₀σ₀)^-1 is the → magnetic diffusivity.

→ magnetic; → diffusion.

Same as → magnetic dip or → dip.

→ magnetic; → inclination.

1) Same as → magnetic flux density.
2) The production of a magnetic field in a piece of un-magnetized iron or other → ferromagnetic substance when a magnet is brought near it. The magnet causes the individual particles of iron, which act like tiny magnets, to line up so that the sample as a whole becomes magnetized.

→ magnetic; → induction.

A hypothetical particle that carries a single → magnetic pole, in contrast to magnets which are north-south pole pairs. These massive particles (billions of times heavier than the → proton) are required by grand unified theories(→ GUTs) to explain the actual matter content of the Universe, particularly the dominance of matter upon → antimatter. However, their existence contradicts → Gauss's law for magnetism.

→ magnetic; → monopole.

A problem concerning the compatibility of grand unified theories (→ GUTs) with standard cosmology. If standard cosmology was combined with grand unified theories, far too many → magnetic monopoles would have been produced in the early Universe. The → inflation hypothesis aims at explaining the observed scarcity of monopoles. The inflation has deceased their density by a huge factor.

→ magnetic; → monopole; → problem.

In a → plasma, a change of → magnetic connectivity of plasma elements due to the presence of a localized → diffusion region. It allows charged particles to move from one → magnetic field line to another. Magnetic reconnection is an important process transforming magnetic energy into heat or/and kinetic energy. Magnetic reconnection events occur in the Earth's → magnetosphere. The process plays an important role in explosive phenomena in the Sun, such as → coronal mass ejections and → solar flares which heat the → solar corona.

→ magnetic; → re-; → connection.

The process by which a magnetic system relaxes to its minimum energy state over time.

→ magnetic; → relaxation.

A phenomenon exhibited by certain atoms whereby they absorb energy at specific (resonant) frequencies when subjected to alternating magnetic fields.

→ magnetic; → resonance.

In → magnetohydrodynamic (MHD) treatment of → plasmas, that component of the → Lorentz force which is directed toward the centre of curvature of the → magnetic field lines and thus acts to straighten out the field lines. The Lorentz force can be decomposed into two components orthogonal to the magnetic field: j× B = (B . ∇) B / μ₀ - ∇ (B² / 2μ₀), where j is the → current density, μ₀ is the → magnetic permeability of free space, and B is the → magnetic flux density. The left side term is the Lorentz force, the first term on the right side is the magnetic tension and the second term the → magnetic pressure.

→ magnetic; → tension.

Radiation emitted by a rotating magnet.

→ magnetic; → dipole; → radiation.

1) General: The process of magnetizing or the state of being magnetized.
2) Electricity: The → magnetic moment per unit volume induced by an external magnetic field; measured in → amperes per meter.

Verbal noun of → magnetize.

The acceleration exerted on the plasma particles according to the → magnetocentrifugal model.

→ magnetocentrifugal model; → acceleration.