An Etymological Dictionary of Astronomy and Astrophysics
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The principle of interconversion of mass and energy, described by the → mass-energy relation.

→ mass; → energy; → equivalence.

The famous equation proposed by Einstein as a consequence of his special theory of relativity describing the equivalence of mass and energy: E = mc², where E is energy, m is the equivalent amount of mass, and c is the velocity of light.

→ mass; → energy; → relation.

The energy that is possessed by an object due to its motion or due to its position. It is equal to the sum of the → kinetic energy and → potential energy.

→ mechanical; → energy.

Energy released during a nuclear reaction as the result of the conversion of mass into energy. → mass-energy equivalence.

→ nuclear; → energy.

The → sum of the → potential energy and the → kinetic energy of an object in → orbit.

→ orbital; → energy.

In nuclear physics, the extra binding energy associated with pairs of nucleons of the same kind. This quantity expresses the fact that nuclei with odd numbers of neutrons and protons have less energy and are less stable than those with even numbers of neutrons and protons.

Pairing, verbal noun of → pair; → energy.

The unit of energy in the system of Planck units. E_P = √ (ħ c⁵/G) ≅ 1.22 x 10¹⁹ GeV. It can also be defined as E_P = ħ / t_P, where t_P is the Planck time. This is an extraordinarily large amount of energy on the subatomic scale and particle accelerators have yet to produce a particle with this magnitude of energy. Understanding the properties of a subatomic particle that contains the Planck Energy is helpful in developing a Unified Field Theory which encompasses the realms of Quantum Theory and Relativity, although this too has evaded complete scientific understanding.

→ Planck; → energy.

Of a system, the work done in changing the system from some standard configuration to its present state. Thus, if a body of mass m is raised vertically through a height h, the work done, mgh, is the increase in potential energy.

→ potential; → energy.

A plot that displays the → potential energy of a moving body as a function of its position. It is explained by the → conservation of energy and the conversion of potential energy into → kinetic energy and vice versa.

→ potential; → energy; → curve.

The energy that is transmitted in the form of → radiation, in particular as → electromagnetic radiation.

→ radiant; → energy.

The energy which a particle has when it is at rest. According to Einstein's → mass-energy relation, it is equal to the → rest mass times the square of the → speed of light: E = mc².

→ rest; → energy.

Same as → rest energy.

→ rest; → mass; → energy.

The → kinetic energy of rotational motion of an object. It is expressed by E_R = (1/2)Iω², where I is the → moment of inertia and ω → angular velocity (2π/P).

→ rotation; → energy.

The → kinetic energy due to the → rotation of and object. Rotational energy is part of the total kinetic energy of the body. It is given by: (1/2)Iω², where I is the → moment of inertia and ω is the → angular velocity. Same as → angular kinetic energy.

→ rotational; → energy.

Same as → Weizsacker formula.

→ semiempirical; → binding; → energy; → formula.

The energy required to remove a particle (a proton or a neutron) from a particular atomic nucleus.

→ separation; → energy.

The energy which → sound waves impart to a medium. Same as acoustic energy.

→ sound; → energy.

A plot showing the energy emitted by a source as a function of the radiation wavelength or frequency. It is used in many branches of astronomy to characterize astronomical sources, in particular mainly in → near infrared and → middle infrared to study → protostars or → young stellar objects. The SED of these objects is divided in four classes.
Class 0 in which the SED represents a very embedded protostar, where the mass of the central core is small in comparison to the mass of the → accreting envelope. The SED is characterized by the → blackbody radiation of the envelope and peaks at → submillimeter wavelengths.
Class I objects possess a SED that peaks in the → far infrared and is characterized by a weak contribution of the blackbody of the central protostar (detected in near infrared) and the emission of a thick disk and dense envelope. These objects have less mass in the envelope and more massive central cores with respect to Class 0.
Class II objects are the → classical T Tauri stars with a SED due to the emission of a thin disk and the central star. They have accumulated most of their final mass and have dispersed almost completely their circumstellar envelope.
Finally, Class III objects have pure photospheric spectra. Their SED is peaked in the optical and is well approximated by a blackbody emission with a faint → infrared excess due to the presence of a residual optically thin disk that may be the origin of → planetesimals.
This classification scheme can be made more quantitative by defining a → spectral index.

→ spectral; → energy; → distribution.

The splitting of a single atomic level into a group of closely spaced levels when the substance producing the single line is subjected to a uniform magnetic field. → Zeeman effect; → Stark effect.

→ spliting; → energy level.

The total amount of energy liberated by a → supernova. A typical supernova radiates between 10⁵¹ and 10⁵²  → erg, or 10^44-45 J (→ joules).

→ supernova; → energy.