By J. Bovy (2015)
What it does
galpy provides gravitational potentials for the Milky Way, among them MWPotential2014 and McMillan17 (McMillan 2017), and integrates orbits in them with Python and C integrators. It computes action-angle coordinates and orbit parameters such as the eccentricity, the maximum height above the plane (z_max), the pericentre and the apocentre, among them through the Stäckel approximation (Binney 2012).
Given a star's position, distance, proper motion and radial velocity, it returns the path the star follows through the Galaxy and the conserved quantities that label it. galpy is written by J. Bovy (2015) and is open source.
How I used it
I use galpy for orbit parameters (the Stäckel approximation, in the McMillan17 potential) in work in preparation. I also use it in my ArqueoGal data repository, which assembles extinction, distances and galpy kinematics for Gaia DR3 and APOGEE DR19 stars, for the FCT ArqueoGal project.
The animation
The star is Gaia DR3 5474633394457737216, a red giant chosen at random from the Gaia archive. Its position, parallax, proper motion and radial velocity are the Gaia DR3 values, with the distance taken as the inverse of the parallax. The orbit is integrated with galpy 1.12.1 in McMillan17 over 1.2 billion years. The ring is built from the same orbit integrated over 10 billion years. The shapes of the disc and bulge light follow McMillan (2017).
The brightness of the Galaxy, the colours and the camera are drawn. The scattered disc stars are visual texture only and stand for no Gaia star or catalogue. The look of the star is that of the site's rendered star, which stands in for the surface of this giant, and its size against the Galaxy is a jump in scale.