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Published online by Cambridge University Press: 07 February 2017
Bright fine mottles seen on the solar disk are identified as the agency that locates the Sun on the K-line width-absolute magnitude relation of Wilson and Bappu. The contribution of the supergranular network emission and the plage emission from centres of activity tends to upset the uniqueness of the relation. The line width-absolute magnitude relation is thus a characteristic of the convection zone underlying the stellar atmosphere.