ASTRONOMICAL COMPLICATIONS
Astronomical complications are all functions or indications that depend on celestial bodies and their positions. The information from a simple or complex calendar, moon phases, or even a precise star chart are all considered astronomical complications.
DATE
The date corresponds to the ordinal number of the day within the month, typically ranging from 1 to 31. Watches usually display the date either through the aperture on a dial or with the hand day indicator.
WEEK DAY
Displaying the seven days of the week is one of the simplest complications. In most cases, the days of the week are indicated by a disc showing the current day in an aperture or by a hand on a subsidiary dial. In some instances, the day of the week display may also be of the retrograde type.
MONTH
This complication involves displaying the current month of the Gregorian calendar. This information is typically provided in addition to, at the very least, the date indication. The month display is commonly found on simple calendars as well as annual, perpetual, and secular calendars.
MOONPHASE
The moon phase display shows the progression of the lunar cycle (or the moon’s age). Astronomically, the average length of a synodic month (lunar cycle) is 29 days, 12 hours, 44 minutes, and 2.8 seconds — that is, 29.530589 days.
SIMPLE CALENDAR (TRIPLE CALENDAR)
This type of calendar displays the date, day, month, and sometimes the moon phase. The mechanism does not account for months with 28, 29, or 30 days and therefore requires manual correction five times per year.
ANNUAL CALENDAR
Ce type de calendrier affiche la date, le jour, le mois et parfois la phase de lune. Ce mécanisme ne tient pas compte des mois de 28, 29 et 30 jours et nécessite donc de corriger manuellement la date cinq fois par an.
PERPETUAL CALENDAR
The perpetual calendar is a complication that displays a calendar taking into account the varying lengths of months — 28, 29, 30, and 31 days. It only requires adjustment in secular years that are not divisible by 400 (e.g., 2100, 2200, 2300, 2500, etc.).
SECULAR CALENDAR
Like the perpetual calendar, it takes into account the varying lengths of months—28, 29, 30, and 31 days—across the four-year leap year cycle. However, the secular calendar also accounts for exceptions, namely the secular years that are not divisible by 400, such as 2100, 2200, 2300, and 2500.
EQUATION OF TIME
The equation of time indicates the difference, in minutes, between true solar noon (when the sun is at its zenith at a given location) and mean solar noon. Mean solar time is what our watches display: a constant 24-hour day that represents the annual average of true solar days, whose actual astronomical duration varies depending on the Earth’s position in its elliptical orbit around the Sun.
INDICATION OF THE SEASONS, EQUINOXES, SOLSTICES & ZODIAC SIGNS
Indication normally has a hand that makes one turn in a year that indicates the four seasons and points to the two equinoxes and the two solstices, as well as sometimes the signs of the zodiac.
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