Piaget Limited Serie Mode D'emploi page 8

580P - 584P
EXPLANATION OF THE FUNCTIONS
THE MOON-PHASES INDICATORS
Watches with moon-phases indicators depict the cycle of the moon (new moon, first quarter,
full moon, last quarter) on their dials.
As the moon orbits the Earth, the relative positions of the sun, Earth and moon change
constantly. The phases of the moon correspond to the illuminated half of the moon being
visible from different angles; they are therefore not due to the shadow cast by the Earth on
the moon. The moon merely reflects the light of the sun on the Earth.
The phases of the moon depend on the relative positions of the sun, moon and Earth.
The moon is full when the sun and moon are on either side of the Earth. However they
become invisible (new moon) when they are both aligned on the same side of the Earth.
The first lunar phase is the newmoon. The main feature of this phase is the invisibility of the
moon in the sky. At this precise moment, the moon is located between the sun and the Earth.
Little by little, the illuminated side of the moon becomes visible to the human eye as it moves
around the Earth. At first, a slim crescent can be observed in the evening sky and, as the days
pass, the crescent becomes thicker and remains visible for increasingly longer periods of
time. After the full moon, the visible part of the moon diminishes.
A complete cycle is called a lunation, or lunar month, and corresponds to the duration
between two full moons (synodic period). It lasts 29 days, 12 hours, 44 minutes and 2.8
seconds, or approximately 29.530588 days.
1 2
SELF-WINDING MECHANICAL MOON-PHASES
MOVEMENTS
The Piaget moon-phases is said to be "astronomical". The wheel that indicates the moon
has 135 teeth. With this system, the precision of the lunar month is 29 days, 12 hours and 45
minutes (29.53125 days as opposed to 29.5 days in general). The gap between this mechanism
and the true lunar cycle thus only amounts to one day every 122 years (instead of one day
every 3 years in general). The complication is modelled on the Northern hemisphere.
15 night 11 night 7 night 4 night
th th th th
First quarter First crescent
(quadrature)
Gibbous moon
Earth
Full moon
(opposition)
Last quarter
Gibbous moon
(quadrature)
18 night 22 night 26 night
th nd th
The complication is symbolized by a disc bearing the moons and rotating according to the
lunar calendar. The dial reveals the shiny part of the moon, which illustrates the interplay
between the sun and the Earth perfectly.
1 3
Night 0
New moon
(conjunction)
Sun
Last crescent
29 night
th