Observational geometry as a function of time. The S3 observations are made with the HI-1 wide-field camera (solid lines) and COR2 coronagraph (dotted lines) on STEREO-A. After DOY 350, S3 is detected by the LASCO/C3 coronagraph on SoHO (solid lines). Perihelion is at UT 2020 December 12.67, indicated by the gray vertical line. Heliocentric distance, phase angle, and elongation are represented by red, green, and purple, respectively. Calendar dates are indicated along the top axis.