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Using the 2004 Venus transit of the Sun to constrain a semi-empiricalpoint-spread function for the TRACE EUV solar telescope, we have measured theeffect of stray light in that telescope. We find that 43% of 171A EUV lightthat enters TRACE is scattered, either through diffraction off the entrancefilter grid or through other nonspecular effects. We carry this result forward,via known-PSF deconvolution of TRACE images, to identify its effect on analysisof TRACE data. Known-PSF deconvolution by this derived PSF greatly reduces theeffect of visible haze in the TRACE 171A images, enhances bright features, andreveals that the smooth background component of the corona is considerably lessbright (and hence much more rarefied) than commonly supposed. Deconvolutionreveals that some prior conlclusions about the Sun appear to have been based onstray light in the images. In particular, the diffuse background "quiet corona"becomes consistent with hydrostatic support of the coronal plasma; featurecontrast is greatly increased, possibly affecting derived parameters such asthe form of the coronal heating function; and essentially all existingdifferential emission measure studies of small features appear to be affectedby contamination from nearby features. We speculate on further implications ofstray light for interpretation of EUV images from TRACE and similarinstruments, and advocate deconvolution as a standard tool for image analysiswith future instruments such as SDO/AIA.

Solar Coronal Structures and Stray Light in TRACE