# Time scale

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Time scale may refer to:

In astronomy and physics:

• Dynamical time scale, in stellar physics, the time in which changes in one part of a body can be communicated to the rest of that body, or in celestial mechanics, a realization of a time-like argument based on a dynamical theory
• Nuclear timescale, an estimate of the lifetime of a star based solely on its rate of fuel consumption
• Thermal time scale, an estimate of the lifetime of a star once the fuel reserves at its center are used up

In cosmology and particle physics:

• Planck time, the time scale beneath which quantum effects are comparable in significance to gravitational effects

In mathematics:

• Time-scale calculus, the unification of the theory of difference equations with differential equations

In music:

In project management:

• Man-hour, the time scale used in project management to account for human labor planned or utilized

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In astrophysics, the thermal time scale or Kelvin-Helmholtz time scale is the approximate time it takes for a star to radiate away its total kinetic energy content at its current luminosity rate. Along with the nuclear and free-fall time scales, it is used to estimate the length of time a particular star will remain in a certain phase of its life and its lifespan if hypothetical conditions are met. In reality, the lifespan of a star is greater than what is estimated by the thermal time scale because as one fuel becomes scarce, another will generally take its place – hydrogen burning gives way to helium burning, which is replaced by carbon burning.

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