The Two Moons of Kuha
Key characteristics of the two moons of Kuha, and the tidal consequences of their being.
Kuha is a super continent on an unnamed planet (Planet H) which is orbited by two satellites. Different peoples at different times call these satellites by different names, so here we will simply call them Luna 1 and Luna 2. The details of the two moons provide the foundations of climate, and the geographical details of Kuha.
Key Characteristics
Luna 1 is three‑quarters the mass of Earth’s Moon at 5.507 × 10²² kg, with a diameter of 3,156km. Being slightly smaller than the Moon, but being a distance of 306 000 km away from the planet, Luna 1 appears larger in the sky than the Moon by about 25%. The orbital period is about 19.83 days.
Luna 2 is significantly smaller - about an eighth of the Moon’s size with a mass of 9.178 × 10²¹ kg and a diameter of 1,736km. It is about 586 000 km away from Planet H, with an orbital period of around 60 days. It would appear roughly 25% the size of the Moon. The orbital period is about 60 days.
| Luna 1 | Luna 2 | Earth Moon (ref) | |
|---|---|---|---|
| Mass | 5.507 × 10²² kg | 9.178 × 10²¹ kg | 7.342 × 10²² kg |
| Radius | ~1,578 km | ~868 km | 1,737 km |
| Diameter | ~3,156 km | ~1,736 km | 3,474 km |
| Distance | 306,000 km | 586,000 km | 384,400 km |
| Apparent sky size | ~25% larger than our Moon | ~25% of our Moon | baseline |
| Orbital period | ~19.83 days | ~ 60 days | 27.3 days? |
| Synodic period | ~29.6 days | ~70.330 days | 29.5 days? |
Orbit and consequences for tides
Given that the two satellites have varying orbital periods, there is a gradient of “double full moons”. A near perfect alignment that lasts only 3-4 hours occurs approximately every 563 days - once every 1.38 years, making it a significant event due to its relative rarity. More commonly, near alignments occur about 8 times a year, where one of the two moons is full and the other is within 1 to 3 days of being full.
| Alignment Quality | Interval | Occurrences per planetary year (408 days) |
|---|---|---|
| Roughly full together (within 2–3 day) | Every ~62–70 days | Approx. 6 times per year |
| Noticeably close (within 1 day) | Every ~208 days | Approx. 2 times per year |
| Near-perfect (3-4 hours) | Every ~563 days | Once every 1.38 years |
Correspondingly, there is a gradient of “double new moons”. The darkest possible night where both moons are dark occurs every 563 days - the same interval as the double alignment. It occurs halfway through the approximately 563-day cycle, i.e. roughly 281 days after each double alignment. Luna 1’s 20.843-day cycle means complete single-moon darkness occurs roughly every 10 days, while Luna 2’s slower cycle means its contribution to darkness is less frequent but longer-lasting when it occurs.
Every four years the double alignment cycles come full circle. The double alignment advances by roughly 154 days each year (563 − 408 = 155), cycling through the calendar over roughly 3.6 years before returning to the same month. If a year begins with a double full moon event, the third year will have no double alignment at all, while the fourth year would begin with one again, with the same sequence as the first year.
The two satellites produce a complex tidal system with significant power. Luna 1 with it’s orbit of approximately 20 days is mostly responsible for the tidal patterns found across Planet H, but Luna 2 adds an extra layer of complexity.