sundial1

I have always had a sundial in my garden. It keeps you in touch with the movement of the Sun during the day and during the seasons.

My basic horizontal sundial shows a shadow from its style onto a surface marked with lines indicating the hours of the day. The style is the time-telling edge of the gnomon, the straight edge. As the sun moves across the sky, the shadow-edge aligns with hour-lines.

Sundials that directly measure the sun’s hour/angle must have that edge parallel to the axis of the Earth’s rotation to tell the correct time throughout the year. The style’s angle from the horizontal should equal the sundial’s geographical latitude, but in most inexpensive sundials the hour angles are off and cannot be adjusted. There are many other types of sundials.

Isaac Newton developed a convenient and inexpensive reflection sundial using a small mirror placed on the sill of a south-facing window. The mirror casts a single spot of light on the ceiling and, depending on the geographical latitude and time of year, the light-spot on the ceiling was drawn large enough to be accurate.

Most mass-produced sundials are not the most accurate timekeepers, but in mid-April time by the sun and time by my clocks agrees. Noon is noon in both places.

I adjust my sundial as the months move past me, but I suppose that is a bit of a cheat. This weekend the length of the day as measured by the midday sun is slightly less than 24 hours long. This discrepancy between my watch and the Sun accumulates until mid-May when noon on my sundial will be a few minutes earlier than the clock. After that the sundial middays will become slightly more than 24 hours long and by mid-June, they will match up again.

Cycles. Very much a part of our lives, whether we pass attention to them or not.

 

Sundial Bridge, Redding Ca. The white pylon is 218 feet tall and the Sundial Bridge free spans 500 feet across the river. The Sundial is functional and the northern shoreline has markings with the summer solstice and time of day.

 

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