NOCTURNAL - Use the Stars to tell the Time [improved version]

This is an improved version of the original design at:  NOCTURNAL - Use the Stars to tell the Time [original design] by 3DMason | Download free STL model | Printables.com

The Nocturnal, sometimes also referred to as a horologium nocturnum (time instrument for night), or nocturlabe (French), is related to the astrolabe and sundial.  It is a universal device which indicates local mean time from the position of the stars during different times of the year.  Here's a picture of one dating back to 1781 which was used by sailors:

Most Nocturnals consist of the following main parts:

• an outer disc marked with the months of the year with subdivision for days;

• an inner disc marked with hours and quarter hours (on the larger instruments);

• tooth or tab for one or more reference stars;

• a pointer rotating on the same axis as the discs & sometimes extended beyond the rim;

• an axis, or pivot point with hollow center such that Polaris can be sighted through it.

Design Details

The original design was based on a card stock template which was downloaded from:  The Sundial Primer - The Nocturnal and measured 130x103x13mm.  Unfortunately, the template graphics were not great.  This updated version was completely redone to provide better readability of the discs, including the addition of a How to Use guide placed at the back of the outer disc.

A great thank you goes out to the originator Carl Sabanski.  Check out his cool sundial website:  https://www.mysundial.ca/tsp/tsp_index.htm

The hour disc consists of three teeth that are used to reference one-of-three different stars, all of which are located near the North Star, Polaris. They are:

• BD - "Big Dipper", or "Ursa Major" and references to the Pointer stars;

• LD - “Little Dipper” or "Ursa Minor" and references to the star Kochab;

• CA - "Cassiopeia" and references to the star Schedar.

The figure below shows these three constellations with their respective reference stars in relation to Polaris:

Construction Details

Consider printing with a glow-in-the-dark PLA filament to make it easier to see the markings at night.  Preferably red so as not to affect your night vision.  The assembly is very simple.  All pieces fit over top of each other, with the pointer snapping into the center holes of both inner & outer discs.  The outer disc is the larger piece with the handle at the bottom.  No additional hardware is required.

How to Use 

1. First decide which of the 3 reference stars is the most visible in the night sky;

2. Align the flat edge of your inner (hour) disc tooth of your chosen reference star; i.e. BD, LD or CA, with the current month & date located on the larger (month) disc;

3. Hold the instrument in a vertical position away from you with the handle pointing down towards the ground;

4. Sight the North Star (Polaris) through the hole at the center of the instrument;

5. Rotate the pointer until its indicating edge points to the chosen reference star;

6. Read the indicated local mean time from the inner hour disc from the edge of the pointer;

7. To obtain standard time, longitude correction needs to be applied to the reading.

If you think this is a cool design, don't forget to hit the like button. I hope you enjoy building this & thanks for your support!

References

1. NOCTURNAL - Use the Stars to tell the Time by 3DMason | Download free STL model | Printables.com

2. The Sundial Primer - The Nocturnal