Possible sky-projected orbit of KELT-20 induced by a companion, shown for the best-fit solution (Section 2.3). Left: motion of the host star between the Hipparcos and Gaia epochs (1991–2016), color-coded by time. The axes show R.A. (﹩\alpha * \equiv \alpha \cos \delta ﹩) and decl. (δ), with the origin at the center of mass. Right: illustration of proper-motion vectors from Hipparcos (blue), Gaia (orange), and Hipparcos-Gaia (HG; red). The HG vector points along the displacement vector between Hipparcos and Gaia epochs (gray dashed line). It is much shorter than the others because it is based on the net displacement over ∼25 yr, during which the star completed several orbits and returned to nearly its original position as shown in the left panel.