A fragment of the butterfly diagram around the gap between the southern wings of cycles 8 and 9. Sunspot groups belonging to cycle 8 are plotted in grey and cycle 9 groups in black. The centres of all the detected gaps longer than the threshold gap length of Table 4 are plotted in black circles. The fitted line up to −28° and the vertical line poleward of −28° between the wings are plotted in black.