Epochra: Precession of the Equinoxes
Cosmology & the Sky arc, page 166 of 193. Back to The Pixelated Physics Universe
Who they are
Epochra has one line, and says it often: “Wrong epoch. wrong sky.”
Epochra is a character of the Cosmology & the Sky arc: drawn in pixels, ruled by one piece of real physics, and never allowed to break it.
The physics
General precession in longitude is about 50.3″ per year; coordinates must specify the epoch (J2000).
$$ \begin{gathered} p_A \approx 5028.796195''\ \text{per Julian century} \approx 50.3''\,\text{yr}^{-1} \\ P = \frac{360^\circ}{p_A} \approx 25\,800\ \text{yr} \end{gathered} $$
| Symbol | Meaning | SI unit |
|---|---|---|
| $p_A$ | general precession in longitude | — |
| $P$ | precession period | yr |
Sources
Crossovers
Epochra meets Wobbleon (Chandler Wobble). Wobbleon's pole wanders by metres within the crust. Epochra's axis precesses in space, about 50.3″ per year, because the Sun and Moon pull on the equatorial bulge. Different motions, both measured with care by astronomers.
Epochra meets Siderelle (Sidereal Day). Siderelle's day measures Earth's spin against the stars. Epochra's precession slowly moves the reference point itself, which is why star catalogues must state their epoch.
Wear the lore
Concept keywords: Precession of the Equinoxes, Epochra, Cosmology & the Sky, physics lore, Pixelated Physics