A map showing the approximate viewing geometry from LOFAR station RS508 towards Cygnus A on 14th July 2018 at 17:50 UT. Cygnus A was at an azimuth of 65° and an elevation of 34°. The eastward end of the yellow line corresponds to an ionospheric pierce point at an altitude of 350 km and the eastward end of the orange part of this line corresponds to an ionospheric pierce point at an altitude of 120 km. The blue line indicates the position of the ionospheric pierce point at an altitude of 350 km between 17:00 UT and 17:59 UT.