Magnetograph Observations of the Quiet Sun. I. Spatial Description of the Background Fields

A photoelectric magnetograph is described which achieves an rms noise equivalent sensitivity of 1 gauss (arc sec)-2 sec'. The dynamic range is 0 5-4000 gauss Fine-scan maps of the center of the disk, 45000 x 52000 km, show Ca~ K-emission associated fields of `-~-`1O0 gauss and background fields of `-`lO gauss. Both the K-emission fields and background fields resolve into elements of about the same size, 1000-2000 km, when measured at the half-intensity point The integrated flux contained in the back- ground fields was never zero (1965-1967) but ranged from 0 25 to 0 5 of the flux in the K-emission ele- ments. The background fields are suggested to he remnants of old K-emission fields reduced in strength, but not size, by the action of the supergranulation. Previously reported upper limits to a granular mag- netic field probably represent measures of these relatively large supergranule-related elements. Single line scans made with an aperture of 360 X 360 km achieve an effective resolution of 500 km when the seeing is good While velocity and brightness elements in the quiet Sun exhibit a spatial fine structure down to this observational resolution limit, no similar fine structure is found in magnetic fields