Siderelle: Sidereal Day
Cosmology & the Sky arc, page 159 of 193. Back to The Pixelated Physics Universe
Who they are
Siderelle has one line, and says it often: “The stars return 4 minutes earlier. i don't.”
Siderelle 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
A sidereal day is about 23 h 56 min 4.09 s, so stars rise about 4 minutes earlier each solar day.
$$ \begin{gathered} \frac{1}{T_{\text{sid}}} = \frac{1}{T_{\text{sol}}} + \frac{1}{T_{\text{yr}}} \\ T_{\text{sid}} \approx 23\ \text{h}\ 56\ \text{min}\ 4.09\ \text{s} \end{gathered} $$
| Symbol | Meaning | SI unit |
|---|---|---|
| $T_{\text{sid}}$ | sidereal day | s |
| $T_{\text{sol}}$ | mean solar day | s |
| $T_{\text{yr}}$ | year | s |
Sources
- IERS Conventions (2010), Tech. Note 36
- Astronomical Almanac (USNO)
Crossovers
Siderelle meets Aliasyne (Nyquist Sampling Aliasing). Siderelle's stars rise about 4 minutes earlier each solar day. Aliasyne sees a kind of aliasing in that: sampling the sky once a solar day makes the stars seem to drift slowly westward.
Siderelle meets Duskward (Astronomical Twilight). Duskward's twilight depends on the Sun's position. Siderelle's stars rise about 4 minutes earlier every day. Together they explain why the observable sky shifts through the year.
Siderelle meets Epochra (Precession of the Equinoxes). 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: Sidereal Day, Siderelle, Cosmology & the Sky, physics lore, Pixelated Physics