Paper detail

Uniformity of the quiet solar disk: 3130 - 46700 Å

Taking advantage of the absence of solar activity in the recent 2008-9 epoch (no spots, few faculae), we have made equatorial and meridian disk scans in continua from 3129 Å to 46700 Å. Averaging 20 scans at each wavelength to suppress granulation, which takes a total of 35 minutes, we achieve a system noise level of 0.01%. We believe this noise level is a record low, not because of instrument improvements, but simply because of observing procedures and the cooperation of the Sun and sky. The observed solar fluctuations significantly exceed the noise and range from 0.3% at 3130 Å, 0.05% at 34000 Å, to 0.06% at 46700 Å near disk center. These fluctuations (corresponding to about 3 K) presumably arise from the incomplete averaging of granulation. Standard solar models for limb darkening fit the data for true continuum regions reasonably well. No significant differences are seen between scan directions (EW, N-S). Perhaps our results can serve as a template for exoplanet detection by the transit of quiet G2V-like stars.