For parabolic orbits, in place of the semi-major axis of the ellipse \(a\), we use the perihelion distance \(q\), and in place of the epoch time we use the time of perihelion passage \(T_{p}\). In the...For parabolic orbits, in place of the semi-major axis of the ellipse \(a\), we use the perihelion distance \(q\), and in place of the epoch time we use the time of perihelion passage \(T_{p}\). In the case of a body orbiting the Sun, \(G M\) is the graviational constant of the Sun, equal to \(1.32712440041 \times\) \(10^{20} \mathrm{~m}^{3} \mathrm{~s}^{-2}\).
