### Local Thermodynamic Equilibrium

**(LTE)**
(state where temperature variation is too small to matter)

**Local Thermodynamic Equilibrium** is a condition,
e.g., of some gas, such that the variation in Temperature
is small enough that "constant temperature" is a useful approximation,
i.e., it can be usefully treated as if in Thermodynamic Equilibrium.
If processes under study directly affect matter only within
sufficiently short distances, then assuming a
constant temperature can be a useful approximation.
The term is also used for the model that assumes the condition.

The term **NLTE** (for **Not** or **Non Local Thermodynamic Equilibrium**)
is used for an amended LTE-like model that accommodates
a common discrepancy from true LTE,
specifically, excess Electromagnetic Radiation invading the locality.
Like LTE, it is an approximation used to make stellar models
(and other models) tractable.
The terms **Kinetic Equilibrium** and **Statistical Equilibrium**
are sometimes used as an alternative to "NLTE" since
the term NLTE might literally be taken to mean
"global Thermodynamic Equilibrium"
or to mean any other concept that isn't LTE.

(*thermodynamics,astrophysics*)
http://en.wikipedia.org/wiki/Thermodynamic_equilibrium

https://arxiv.org/pdf/1406.3553.pdf

**Referenced by:**

Photosphere

Stellar Structure

Thermodynamic Equilibrium (TE)

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