How to Read the Dial

Like a clock that strikes only on the hour, the dial is designed to show standard clock time on the hour. Analemmas define the course of the sun’s shadow each daylight hour over the course of the year. When the shadow of the tip of the gnomon is exactly underneath the analemma, the time corresponds to the number above the analemma for Pacific Standard Time or the number below for Pacific Daylight Time.

Since the figure-8 analemma usually has two sides, except where it criss-crosses, on about 4/15 and 8/29, the correct side to use is determined by the First Day of the month markers. In the photo above, taken on February 11th, the left side of the analemma shows shadow positions for 2/1 and 3/1, indicating the left side should be used. 

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Above: The gnomon shadow is between the 11/1 and 12/1 markers, so time is read on the right side of the analemma. It is 9:00 AM, PST on 12/3/2023. The 12/1 metal ball marker is placed a little too high; it was tricky to superglue the balls in the exact position.

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Above: The 12/1 marker ball is more accurately placed; this picture was taken 12/1/2023 at 2:00 PM PST.

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Above: The gnomon shadow is over the 8/23 declination line . The marker ball for 8/1 is on the left side of the analemma. It is 4:00 PM PDT on 8/23/2023.

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Above: The shadow tip is between the 11/1 and 12/1 markers. It is 8:00 AM PST, 11/4/2023.

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Above: The shadow tip is underneath the 4:00 PM analemma wire – the sun is low in the sky and the analemma itself casts a shadow, but that should be ignored. The gnomom shadow tip is between the 11/1 and 12/1 markers. The photo was taken 11/25/2023, 4:00 PM PST.

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Above: Around noon, the shadows are very short. The dial still retains acceptable accuracy. The shadow tip touches the 12/1 marker. Photo taken 11:00 AM PST, 12/1/2023.

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Above: Photo taken 5/20/23. The shadow tip is very close to the declination line seperating Taurus (orange) and Gemini (red), It is between the 5/1 and 6/1 markers, which are on the right side of the analemma. It is exactly 10:00 AM PDT.

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Above: Photo taken 2/21/2024 at 5:00 PM PST. The declination line between Aquarius (blue) and Pisces (green) comes early in 2024, on February 18th, since we are just shy of adding another day to the calendar on 2/29/24. The shadow tip just touches the 5 PM analemma and is already well into Pisces. Note how the distance between 2/1 and 3/1 markers is shorter than the distance between 3/1 and 4/1. At the Equinoxes, the tilt of the earth’s axis maximizes the north-south apparent motion of the sun, causing daylight hours to lengthen or shorten quickly. The first of month markers therefore register a greater north-south excursion. At the solstices, the axis of the earth is either tilted toward or away from the sun. Note the 12/1 and 1/1 markers at 4 PM PST show mostly east-west motion, due to the effect of the elliptical orbit of the earth.

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Above: Photo taken 7:30 AM PST, 2/23/2024. The shadow tip just touches the left side of the 7:30 AM analemma. The tip has moved closer to the 3/1 marker ball and the Equinox center line.

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Above: Close up, 2/23/2024, 7:30:09 AM PST. Within 22 seconds, the shadow tip will already have moved further east, away from the analemma:

Above: Photo taken 2/23/2024 at 7:30:31 AM PST. After nearly one year’s observation, the dial maintains excellent accuracy. In the early AM and late PM hours, it is within one minute of standard time. In the mid-days hours short shadows and the blunted shadow of the gnomon tip make precise measurement to the minute more difficult.