Estimation of auroral altitude using photograph taken by citizen scientist and satellite-derived magnetic field line. (a) The magnetic field line of the satellite location (red marker) is shown by black solid line. The lines-of-sight of 0-, 10-, 20-, 30-degree elevation angles are shown by red, green, blue, magenta solid lines. Each estimated altitude is indicated by the corresponding dotted curve, with altitudes of 220 km, 480 km, 800 km, and 1110 km. (b) The altitude distribution of auroral emission was visualized by superimposing an altitude grid on the photograph.