Expansion of the AT Cnc ejecta blobs was calculated following the fluid drag equation (Williams 2013). For input parameters and details, see Sects. 4 and 5 and Appendix D. The solution ranges are shown for initial expansion velocities of 3000 (grey), 670 (red), and 1200 km s⁻¹ (blue), the latter to differentiate between fast and slow novae. (We show 670 km s⁻¹, the minimum initial expansion velocity for Sedov-Taylor solutions, for better comparison with Fig. 2.) Left: Evolution of shell radius. Right: Evolution of expansion velocity. The current radius and velocity (in 2016) of the AT Cnc ejecta (horizontal lines) are reached simultaneously for an age range of ca. 128–631 yr (dash-dotted green lines).