Figure 17-2: Stellar Parallax (a) As Earth orbits the Sun, a nearby star appears to shift its position against the background of distant stars. The parallax (p) of the star is equal to half the angle that the star appears to shift as Earth moves from one side of its orbit to the other. (b) The closer the star is to us, the greater the parallax angle p. The distance d to the star (in parsecs) is equal to the reciprocal of the parallax angle p (in arcseconds): d = 1/p.