What you're seeing
Most of Orion's bright stars belong to the Orion OB1 association —
born together, 250–400 pc away, still travelling together. Their proper motions are tiny
(1–3 mas/yr), so the Belt and the hourglass survive a million years almost intact.
What breaks the figure is the foreground: Betelgeuse at 222 pc,
Bellatrix at 77 pc, and the fast nearby field stars that streak clean out of the frame.
Sirius, Procyon and Aldebaran are marked as landmarks — they are not part of Orion,
and they cross enormous distances.
Run forward and a loose fan of stars sweeps in from the upper right and
crosses Orion around +1 Myr. That is the Hyades — 50 co‑moving stars in this
sample at 47 pc, all sharing a proper motion near 105 mas/yr, streaming toward their
convergent point.
Figure lines fade as the asterism dissolves. Once a member has drifted
more than a few degrees the line dims, and past 14° it is dropped — the pattern has
genuinely ceased to exist rather than being dragged across the sky.
Star sizes track apparent magnitude, so stars swell as they approach
and fade as they recede.
Caveats
Data. Positions, parallaxes and proper motions are from the
Hipparcos‑2 reduction (van Leeuwen 2007, ESA I/311), which remains the reference for
naked‑eye stars — Gaia saturates above G ≈ 3, so Rigel and the
Belt have no usable Gaia DR3 astrometry.
Two stars are overridden. Hipparcos handles Betelgeuse badly — its
vast, asymmetric convecting photosphere shifts the measured photocentre, and the raw
Hipparcos‑2 parallax of 6.55 mas (153 pc) is a known outlier. It uses instead the
Harper et al. (2017) combined VLA/VLBA radio + Hipparcos solution: 4.51 mas
(222 pc), μ = 26.42, 9.60 mas/yr. The Trapezium returns a negative
Hipparcos parallax and uses the Gaia DR3 / VLBA cluster solution.
Radial velocities are literature values for the 32 labelled stars only;
field stars are integrated with vr = 0, which affects their perspective
terms but not their dominant tangential motion.
Extrapolation. Motion is linear — no Galactic potential, no binary
orbits. Over 1 Myr, Galactic tides and differential rotation would perturb these tracks at
the several‑degree level. Proper‑motion errors of ~0.8 mas/yr also compound to
~0.2° of positional uncertainty per star.
Betelgeuse is unlikely to survive the run. It is a ~10 Myr‑old
red supergiant expected to go supernova within roughly 100,000 years.