Fig. 8

The count profile of the zero-order and spectral images of Flash 170201 (2nd-frame). The dark frame and the lunar background have been subtracted. The abscissa shows the distance along the spectral image from an arbitrary point. The atmospheric dispersion elongates the zero-order profile. We used the plots of more than 5000 in count (encircled by the rings) to determine the center of count of the zero-order image (O in the figure). The distance from the center is denoted by x