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., \(v_{\mathrm{esc}}(r) = \sqrt{2[\Phi(\infty)-\Phi(r)]}\).

galpy.potential.evaluatePotentials(Pot, R, z, phi=None, t=0.0, dR=0, dphi=0)[source]

Evaluate a potential or sum of potentials.

  • Pot (Potential or list of Potential) – Potential or list of potentials (dissipative forces in such a list are ignored).

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

  • z (float or Quantity) – Distance above the plane.

  • phi (float or Quantity, optional) – Azimuth (default: None).

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

  • dR (int, optional) – If set to a non-zero integer, return the dR derivative instead (default: 0).

  • dphi (int, optional) – If set to a non-zero integer, return the dphi derivative instead (default: 0).


Potential or potential derivative.

Return type:

float or Quantity


  • 2010-04-16 - Written - Bovy (NYU)