The Octa Lune launched in 2003, two years after the original Octa Automatique, as the moonphase variant of the Octa platform. Where the standard Octa shows hours, minutes, large date, and power reserve, the Octa Lune adds a moonphase aperture at 9 o'clock showing a hand-engraved 18k gold moon disc cycling through the 29.5306-day synodic month. The complication is accurate to one day every 122 years before manual correction is required, far more precise than a conventional 30-day-cycle moonphase (which drifts a day every 2.5 years).
The technical achievement is in the gear ratios: a standard moonphase uses a 59-tooth wheel that advances once every 24 hours, completing the cycle in 29.5 days; the Octa Lune uses a more elaborate train that better approximates the actual lunar cycle of 29 days, 12 hours, 44 minutes, 2.8 seconds. Across 122 years, the watch accumulates one day of drift; over a typical wearing lifetime, the moonphase requires no correction. The 18k gold moon disc itself is hand-finished with a polished surface that catches light differently as the moon rotates.
The dial layout follows the standard Octa visual identity: off-centre time display at 1-2 o'clock, large date aperture at 12, retrograde 5-day power-reserve indicator at 11, moonphase aperture at 9. The dial is typically silvered guilloché on pink-gold variants and silvered or anthracite on platinum. The case is solid 18k pink gold, yellow gold, or platinum, sized at 40mm (most common) or 42mm. The Cal. 1300.3 underneath uses the same solid 18k pink gold bridges and baseplate as every modern Journe automatic.
Octa Lune retail is approximately CHF 50,000-65,000 depending on case material; secondary-market values for clean examples track close to retail or above. Annual production is small (typically 50-100 pieces per year across all variants), and the Octa Lune has remained one of F.P. Journe's most-recognised complications throughout its 20-year run. The watch sits between the time-only Octa Automatique and the more elaborate Calendrier and Souverain references in the catalogue, and is generally considered the most-collectible everyday Journe.