The minimum azimuth difference Δθ between WIND and PSP in the HGI coordinate. The curve marked by the green circles shows all the angles of minimum azimuth difference from 2019 January 1 to 2020 July 31 in a temporal resolution of 1 day. Blue squares label the dates when PSP is in the encounter phases. The red solid line represents the position where Δθ equals 30°.