NATARAJAES-03
Sidereal day and sidereal time
Learning outcomes & permitted supports
- Explain the sidereal day (≈ 23h 56m 04s) and why it differs from the solar day.
- Predict how star transit times drift night to night and month to month.
- Read GMST/GAST as 'which hour circle is on the meridian' — the entry point to star sights.
Supports in this lab: live physical model with freeze-orbit thought experiment, twin clocks, engine-solved transit table.
Sun and star from a moving Earth
Two clocks
Engine readout
| GMST | 18:10:59 |
|---|---|
| GAST | 18:10:59 |
| Eq. of equinoxes | 0.58 s |
| Star RA | 18:41:04 |
| Sidereal gain / solar day | 3m 55.9s |
| Tonight's star transit (UT) | 21:00:00 |
The star's transit, night after night
| Local date | Transit (UT) | Change |
|---|---|---|
| 16 Aug 2026 | 21:00:00 | — |
| 17 Aug 2026 | 20:56:04 | −3m 56s |
| 18 Aug 2026 | 20:52:08 | −3m 56s |
| 19 Aug 2026 | 20:48:12 | −3m 56s |
| 20 Aug 2026 | 20:44:16 | −3m 56s |
| 21 Aug 2026 | 20:40:20 | −3m 56s |
| 22 Aug 2026 | 20:36:25 | −3m 56s |
Computed by solving GAST = star's RA each night with the validated engine — not by adding a memorised constant. The ≈ −3m 56s is a RESULT, and it is why a given star rises about 2 hours earlier each month.