The Sun's immutable basal quiet atmosphere

We employ limb darkening, spectral energy distribution (color), and center-disk spectrum line strength to investigate photospheric temporal variability. Current limb-darkening curves agree to 1% with past observations taken at different epochs extending back to 1975. Concerning color, from the data of Labs and Neckel (Cox, 1999) we deduce that the solar limb is 1000 Angstrom more red than disk center. But when integrated over the entire disk to represent the Sun-as-a-star, the color shift is only 30 Angstrom. Color is therefore not a very sensitive indicator of full-disk photospheric change. We examine the center-disk time series for C 5380 Angstrom and Fe 5379 Angstrom equivalent width and the Ca K index. The ratio C 5380/Fe 5379 in equivalent width is 0.4221+0.00011 (+/-0.00003) y(-1), indicating secular change but with no cycle modulation. Converted to temperature this variance amounts to +/-0.028 K. This is in contrast to the full-disk cycle modulation of these lines reported by Gray and Livingston (1997b). Ca K index also exhibits no cycle variation at disk center. Taking into account these findings, plus the small fraction of the photosphere occupied by magnetic elements as revealed in high-resolution G-band pictures, we suggest that cycle magnetic fields thread through the basal atmosphere without physical effect; that the basal quiet atmosphere is observationally immutable to the magnetic cycle within the limits given above.