galpy potentials do not necessarily approach zero at infinity. To compute, for example, the escape velocity or whether or not an orbit is unbound, you need to take into account the value of the potential at infinity. E.g., \(v_{\mathrm{esc}}(r) = \sqrt{2[\Phi(\infty)-\Phi(r)]}\).

Potential.__call__(R, z, phi=0.0, t=0.0, dR=0, dphi=0)[source]

Evaluate the potential at the specified position and time.

  • R (float or Quantity) – Cylindrical Galactocentric radius.

  • z (float or Quantity) – Vertical height.

  • phi (float or Quantity, optional) – Azimuth (default: 0.0).

  • t (float or Quantity, optional) – Time (default: 0.0).

  • dR (int, optional) – Order of radial derivative (default: 0).

  • dphi (int, optional) – Order of azimuthal derivative (default: 0).


The potential at the specified position and time.

Return type:

float or Quantity


  • 2010-04-16 - Written - Bovy (NYU)