Uploaded April 2018 | Updated September 2026, 2 weeks ago
Shown here is the initial gearing for the sun hand precession within the planisphere module. In this example the hand remains stationary when the plastic disk below is rotated. This was made to demonstrate what later will have a set of gears that will allow the hand to have an annual precession across the sky. In other words, the star plate rotates once in a sidereal day with the sun rotating once in a solar day. A sidereal day is 3 minutes, 55 seconds shorter than a solar day thus after one solar day the sun hand will be just under four minutes ahead of the star plate. So if on January 1st both the sun hand and a point marked on the star plate are aligned at twelve o’clock, the sun hand will advance just under four minutes each day and after one year the sun hand will return to its twelve o’clock position aligned with the mark on the star plate. This is the representation of the sun’s precession across the sky as it relates to its position against the stars.
Shown here is the initial gearing for the sun hand precession within the planisphere module. In this example the hand remains stationary when the plastic disk below is rotated. This was made to demonstrate what later will have a set of gears that will allow the hand to have an annual precession across the sky. In other words, the star plate rotates once in a sidereal day with the sun rotating once in a solar day. A sidereal day is 3 minutes, 55 seconds shorter than a solar day thus after one solar day the sun hand will be just under four minutes ahead of the star plate. So if on January 1st both the sun hand and a point marked on the star plate are aligned at twelve o’clock, the sun hand will advance just under four minutes each day and after one year the sun hand will return to its twelve o’clock position aligned with the mark on the star plate. This is the representation of the sun’s precession across the sky as it relates to its position against the stars.
