Close approaches of PSR B1706-16 and ζ Oph in SigMA 15. Lower panel: Flight paths (colored lines) for the closest approach of PSR B1706-16 and ζ Oph (best case) projected on the sky (Galactic longitude l versus Galactic latitude b at epoch of date). The paths start at their current positions (left) and are subsequently marked by small crosses after every 0.5 Myr of flight time. They end at the closest approach within 0.1 pc of each other 1.5 Myr before present (center). SigMA 15 is shown with an orange circle both 1.5 Myr ago (full line) and now (dashed). The gray dots show the 661 closest approaches of PSR B1706-16 and SigMA 15 (i.e., within 10 pc of each other). Upper panel: Distance, D, versus Galactic longitude, l, for the past flight paths. UCL’s position some 1.5 Myr ago is shown as a full green circle, and its current location is represented by the dotted green circle. These are for the best case in Neuhäuser et al. (2020).