Coronal light reflected by the one mirror that is optimized for visible light is focused onto the square pinhole of the UVCS White Light Channel (WLC). This pinhole has a dimension of 50 micrometers on a side, which opens into an angle of 14 square arcseconds on the sky. There is no spatial resolution in the WLC; all of the light that comes in through the pinhole is summed together in one "pixel."
The WLC is designed to measure the broad-band visible intensity of the extended corona (averaging all photons between about 4500 and 6000 Angstroms) and to determine to what extent this light is linearly polarized. These measurements determine the degree of Thomson scattering in the corona (see "atoms, ions, electrons") and allow us to derive the electron density along the line-of-sight to which the pinhole points.
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