Most grandfather clocks with mechanical movement will have a functioning astrological moon dial. The design of the grandfather clock moon dials varies from a simple image to elaborate detailing.
The moon dial slowly moves clockwise following the 29.5 day lunar cycle. All moon dials have an image of the moon that moves showing the lunar date and position of the moon in the sky. For example, it is the new moon phase when the image of the moon disappears and the moon image will appear at the top of the dial on the 15th day.
The moon dial operates together with the clock movement and needs to be set only once.
Example: If the last full moon was 3 days ago, rotate the moon dial clockwise 3 lunar days so that the moon is centered at lunar day 18 on the lunar arch.
Step 4. The moon dial is now set and will indicate the proper moon phases as long as the clock operates continuously. If the clock stops the moon dial will also stop and can be reset when the clock is started again.
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