On the continuum intensity of the umbra of large sunspots

Spectral observations of large sunspots during the period June 1968 – Dec. 1969 in five wavelength regions between 4795 and 6775 are discussed. Selecting the best observations of two very large sunspots, we find slightly lower umbral intensities than derived by earlier observers. It is suggested that the small difference may be explained by the fact that earlier observers have used an average value, whereas we believe that the minimum value gives a more correct estimate of the umbral intensity.