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Sundials- A Passive Solar Timekeeping Device (Why and How)

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Why Sundials?

Modern Time
In 1967, the International System of Units defined the second as "the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom".  The current global standard, Coordinated Universal Time (UTC) depends upon hundreds of atomic clocks in laboratories around the globe.  We all have to use UTC for certain things, but I argue that our drift away from using the sun as the standard for time is indicative of our disharmony with and irreverence for nature.

Nature's Time
If we want to see time the way plants and animals see it, it helps to have a sundial.  The sundial doesn't need to be very complex.  If it simply and accurately marks noon, then it serves its most important purpose, dividing the day into equal halves.  After all, AM and PM are ante-meridian and post-meridian, meaning before and after midday.  This was especially important to our ancestors who instinctively knew they shouldn't travel further from home after noon or they'd risk trying to return home after the sunset.

Noon no longer established by the sun
Before the 20th century, it was standard to set clocks and watches to noon at the very moment the sun was at its zenith.  Now, the sun is completely disregarded in the measurement of time.  Thanks to time zones and daylight saving, local solar noon is often one or two hours after 12pm.  In extreme cases, solar noon nears 3pm.  For everyone living by UTC instead of by the sun, they unwittingly experience long evenings at the expense of short mornings.

The abomination of daylight saving
Despite its name, daylight saving time ("saving" is singular, not plural) doesn't save any daylight, it simply shifts it from the morning to the evening.  I suspect the reason this highly unpopular practice is maintained is it maximizes consumptive behavior- people are generally more productive before noon and more consumptive after noon.  It essentially gives modern commerce 180+ hours of high consumption hours during the six most consumptive months of the year.  

Returning to solar time
If you're comfortable with UTC, keep using it.  But I argue that no permaculturist would choose to mine and refine caesium to measure its radioactive decay, nor is it very sustainable to rely on the people who do this.  If you're looking for a reliable alternative used by humans longer than any other method, and uniquely fits your local environment, you should try a passive solar timekeeping device.
Britton Sprouse
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How to make a Sundial

You can get extremely creative with a sundial.  I'll only include here some general instructions for basic horizontal and vertical sundials.  Look online or in local libraries for other resources on sundials.  

How it works: The two basic parts of a sundial are the gnomon and the dial.  The conceptual key to understand is you need to make the gnomon parallel to the earth's rotational axis.  This means it will cast a consistent shadow and the hour lines are the easiest to calculate.  Then the gnomon needs to be fixed to a dial with hour lines appropriate for the latitude.

1. Record your coordinates, latitude and longitude.  Ex. 34N 97W
1a. Calculate local solar noon.  The equation is LSN = 4*(Longitude - Time Zone Meridian) + equation of time + Daylight Saving (if applicable)
  -Ex. 4*(97 - 90) + 6 + 60 = 94 minutes after clock noon = 1:34pm is local solar noon.  This is important for knowing whether your sundial tells time accurately or not.  
1b. There's more information on the equation of time here: https://www.sfog.us/solar/sfsundialsx.htm.  The value for the equation of time today is +6 mins, but it can vary from +15 to -16.

2. Pick a location for your sundial.  Since a sundial doesn't work in the shade, choose a place with as little shade as possible, keeping in mind the sun shines from the southern half of the sky in the northern hemisphere.
2a. Decide whether you want a horizontal or vertical sundial.  A horizontal sundial usually requires a pedestal, and a vertical sundial requires a building or post to mount it to.

3. Make your gnomon, including the angle it needs to be for your latitude.  If your sundial is horizontal: the angle of the gnomon will be equal to the latitude of your location; Ex. 34 degrees.  If vertical: the angle of the gnomon will be equal to the co-latitude, meaning 90 - latitude; Ex. 90 - 34 = 56 degrees.

4. Calculate the angles for the hours.  You can use a book or online calculator for this.  
4a. Using tangent coefficients for a unit square can be more accurate than using a protractor by hand.
4b. A vertical dial will only tell time from 6am to 6pm, but a horizontal dial may be able to include hours 5am to 7pm or 4am to 8pm, depending on latitude.
4c. I recommend this site for a good calculator: https://www.blocklayer.com/sundialeng.aspx.  This is for horizontal dials, but if you enter the co-latitude, the lines will be accurate for a vertical dial.

5. Mark your dial, including numerals.  If your gnomon is a significant width, then you'll have to separate the AM and PM sides of the dial by that width (the side of the gnomon that casts the shadow changes at noon).
5a. This is usually the best time to add any embellishments to the dial, such as artistic renderings, quotes, etc.

6. Fix your gnomon to the dial.  It will run the along the noon line(s), and the point opposite the tip should touch the 6am/pm lines.

7. Install the dial.  The gnomon of a horizontal dial should point true north; the gnomon and face of a vertical dial should point directly south.
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Wow. This is so cool. Thank you for sharing your learnings Britton.
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