Temporal evolution and geometric structure of coma Fan A in comet 41P. This image series shows coma and Fan A therein fromtop to bottom on nights 2017 March 26–27, 2017 April 08–09, 2017 April 24–25, 2017 May 16-17, 2017 May 25–26, and 2017 June 14-15 (date format in the panels is year/month/day). All images were taken through the SDSS r filter and have an extension of 16 000 km at the comet in X and Y direction with the nucleus position in the center of the frames. North is up and East is to the left. Left column: isophote pattern. Middle panel: radially normalized version. Right panel: Laplace filtered version. For each night, we present median averaged images of all exposures. Fan A appears in the northern hemisphere of the coma. Noise patterns of the size of the typical pixel window used appear as irregular “salt-and-pepper islands” in the Laplace filtered result. Since the Laplace filter is sensitive to curvature in the pixel flux distribution of the image, the appearance of the fan differs slightly from that in the radially normalized image. The wide structure in the south marks the anti-sunward tail orientation of the comet. Image artifacts due to incompletely removed star trails or charge overflow patterns appear as linear streaks in the images. Between the middle and right panel, small inserts illustrate the results of the fan modeling with the Beisser & Drechsel (1992) model. These inserts show the fan geometry for the solution of the rotation axis and active area location that we consider to best describe the observed fan structure in the coma of 41P.