The dimming of a star’s spectrum by the presence of many hundreds or thousands of weak absorption lines too faint and close together to be individually resolved. In cool stars there can be so many different absorbing atoms or molecules with lines in the visible or ultraviolet part of the spectrum that the spectrum appears to be ‘blanketed’ with them. The energy absorbed must be re-radiated, but this is usually at lower energies (i.e. longer wavelengths); hence the red or infrared part of the spectrum will appear enhanced relative to a star with a non-blanketed spectrum.