Moon Librations

Animations the librations of the Moon: the apparent motion of the Moon as viewed from the Earth

import pyvista as pv

import mirage as mr
import mirage.vis as mrv

Let’s animate the librations of the Moon over the course of a synodic month (the time required for the Moon to complete an orbit with respect to the Sun-Earth line).

dates = mr.date_linspace(
    mr.now(),
    mr.now() + mr.days(mr.AstroConstants.moon_synodic_period_days),
    100,
)
pl = pv.Plotter()
pl.open_gif('moon_librations.gif', fps=20, subrectangles=True)
for date in dates[:-1]:
    mrv.plot_moon(pl, mode='eci', date=date)
    pl.camera.view_angle = 1.0  # The Moon's angular size from the Earth is about 0.5 deg, so let's double that FOV
    pl.camera.focal_point = pl.actors['moon'].user_matrix[
        :3, -1
    ]  # Focal point must be set before position, for some reason
    pl.camera.position = (0.0, 0.0, 0.0)
    pl.write_frame()
pl.close()