Jupiter (CML)
Central meridian longitude · three rotations, one planet
Jupiter is not solid and does not turn as one body, so astronomers keep three clocks for it at once. System I covers the fast equatorial belt, turning in 9h 50m 30s; System II the temperate latitudes on either side, where the Great Red Spot sits, at 9h 55m 41s; System III the magnetic field at 9h 55m 30s, which the IAU treats as the planet’s true rotation because the field is anchored to the interior rather than the visible cloud. What each system reports is the central meridian longitude — the line of Jupiter facing Earth this moment. Observers use it to know when a feature will next come round, and the five-minute gap between System I and System II is the visible fact that the equator overtakes the rest of the planet.
In UTC at 02:02 on October 27, 2026, this calendar read System II · 200.0°. The reading above is live, in your own time zone.
At a glance
- Type
- Another world’s rotation, kept as three clocks
- Origin
- Planetary astronomy; System III was set from Jupiter’s radio emissions
- Day
- 9h 50m 30s at the equator (System I), 9h 55m 41s at temperate latitudes (System II), 9h 55m 30s for the interior (System III)
- Counts from
- No count — a longitude: the line facing Earth
- Where it’s used
- Observers timing features such as the Great Red Spot
- How it’s worked out here
- Each system’s rotation rate, counted on from a reference epoch — a guide to which face is turned toward us, not an ephemeris
Does something here look wrong? Tell us about the Jupiter (CML) calendar.