Thermal Time Scale is the time taken by electromagnetic radiation to reach the surface of the star from the center. In other words, the thermal time scale is the time in which a star would radiate away all its thermal energy if the nuclear energy production were suddenly turned off.
The thermal time scale is estimated using the expression
For the sun, is estimated as years. Thus for other stars, thermal time scale can be calculated as,
For the sun, the thermal time scale is about 1/500 of the nuclear time scale.