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Planisphere Clock

Updated May 21, 2018

A 3D-printed astronomical clock that shows the Sun and stars alongside local civil, solar and sidereal time.

May 21, 2018

Build photos

The completed clock (12-hour version). Wooden frame, white hour ring, and bluish-purple sky dial with stars inside, and a yellow hand pointing to the hour on the white ring and the date on the edge of the blue one. — The completed clock (12-hour version). More images and info coming soon!

This reads: This astronomical clock shows the Sun and stars rotating counterclockwise around the North Star, as they appear to do. The oval represents the current sky view at Dallas' 33 degrees North latitude. The yellow Sun hand indicates: local civil time (the time of day, equivalent to mean solar time adjusted for time zones and daylight savings); local mean solar time (the time according to the Sun, on average); the date; the equation of time (used to convert mean solar time to apparent - true - solar time, or “sundial time”; due to the Earth's tilt and eccentric orbit, the Sun appears to go different rates throughout the year, gaining and losing up to 16 minutes); astronomical zodiac (in yellow: the one the Sun is occluding at this time of year; it's about a month “behind” the astrological zodiac, because Earth's axis has precessed about 30 degrees since the zodiac was established); and the Sun's position in the sky (the point where the Sun hand intersects the ecliptic, which traces the Sun's annual path and runs through the zodiac constellations). The sidereal arrow (printed on the blue dial, at around September 21st), indicates local sidereal time (the time according to the rotation of the stars; because Earth orbits the Sun as well as rotates, the stars rotate slightly faster than the Sun, such that there's one extra sidereal day per year. Astronomers use this because the stars are in the same position at the same sidereal time each day. Mean and apparent sidereal time differ by the Equation of Equinoxes, but only by 1sec at most.) — How to read it.

First place in Class 4 at the 2017 NAWCC National Convention!

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