THE CENTER-TO-LIMB BRIGHTNESS VARIATION OF THE SUN AT LAMBDA=850 MICRONS

The 10.4 m submillimeter telescope of the Caltech Submillimeter Observ atory was used to map the full disk of the Sun on 1991 July 9-10 at a wavelength lambda = 850 mum with an angular resolution of 20.6''. A ma ximum entropy-type deconvolution was performed to correct the map for the broad wings of the telescope beam. The brightness distribution of the resulting map shows (i) a high degree of correlation with correspo nding images in Halpha, the Ca II K line, and with the photospheric ma gnetogram; (ii) a systematic center-to-limb brightening of the quiet S un (almost-equal-to 12% at an offset of 0.94 R.) with no apparent diff erence in the limb brightening between the EW and NS quadrants; (iii) an average contrast of almost-equal-to 11% between active region plage s and the quiet Sun near disk center; (iv) a smaller degree of center- to-limb brightening of active region plages (almost-equal-to 5% at an offset of 0.94 R.), leading to a decrease in contrast between active r egion plages and the quiet Sun from the center to limb. We compare the observed center-to-limb brightness variation of the quiet Sun and pla ges with that expected for several chromospheric models, including tho se which include a 'spicular'' component. We find that although the ob served center-to-limb variation of the quiet Sun at 850 mum is broadly consistent with the chromospheric models of Vernazza, Avrett, & Loese r (1981), it differs in detail. However, no improvement results from t he inclusion of ad hoc models of chromospheric inhomogeneities. The br ightness variation in plages from center to limb is consistent with ex isting models for enhanced chromospheric network.