Sundials

 All you wanted to know about Sundials but didn't know whom to ask

The Willowgate Sundial, following a time-tested tradition, aims to be more than a garden ornament or a cutesy timepiece. Offering a localised reference for planting schedules, we hope it becomes a working part of the Community Garden, guiding the annual activities of our gardeners.

Planting guide using the Willowgate Sundial

For starters, you will need to know which half of the year we are currently in. From January through June, the first half of the year, look for the information on the left half of the sundial. It follows that from July through December, the second half of the year, look for the information on the right half of the sundial.

1. You can see what colored bands exist in the current month for potential planting candidates. As an example in March, the sundial shows you can plant Cilantro, Potatoes, Chard, Mustard, Broccoli, Peas, Lettuce, Cauliflower, Bok choy and Kale.  This information is taken from the Master Gardeners of Santa Clara planting guide
2. Next, check the symbols at the top of the colored band to see whether the crop can be planted by direct seed or by transplant. As an example, the symbol for Potatoes is DD which means direct planting only where for Peas it is TD which means transplant or direct seed.

Notes:

• The reason the sundial months vary in size is that the position of the sun changes at different rates for the different months of the year, traveling slower around the solstices (when months are compressed) and faster in between (when months are expanded). 
• The shadow cast by the gnomon (overhanging part that casts a shadow in a sun-dial) will give you the true solar time tuned to the Bay Area timezone of daylight saving time.

Sundials

Historically, for gardeners, keeping track of where you are in the year has been far more important than knowing the time of day, as planting times, harvest times, and religiously significant days were all important to be marked at the same time every year.  

It's a time-honored tradition that dates back to Stonehenge (2500 BCE) and Nabta Playa (6000 BCE).

Note for nerds, sundials do two things: Determine the position of the sun in the sky, of course, but that's just the start. By using a specially designed gnomon (the shadow-forming overhanging part) the gnomonist (sundial designer) can additionally extract key planting information after adjusting for the Earth's tilt as it follows an elliptical journey around the Sun once every year.

The fact that the Earth rotates on a tilted axis as it orbits in an elliptical path around the Sun means the Sun seems to take different paths in the sky from sunrise to sunset as the year progresses. During summer, in the northern hemisphere, the Sun rises north of east and sets north of west. It appears high in the sky at noon. However, during winter in the northern hemisphere, sunrise and sunset appear farther south along the horizon.

Suffice it to say that our gnomonist, fellow Willowgate gardener Jeff Kaiser, had to use fairly complex mathematical computations, after first localising them to the GPS coordinates of the Willowgate Community Garden.

Willowgate Community Garden Sundial

The Willowgate Sundial is a vertical sundial whose face is perpendicular to the Earth’s surface.  The sundial has hour markings of True Solar Time, using Daylight Savings hours.  That means that true Noon (which is also called Local Noon) when in the Northern Hemisphere the Sun is on the North-South meridian (outside of the tropics, this would be when the Sun is highest or due South) occurs at 1:00 on the sundial.   

For the nerds, The Pacific Time Zone is set for the average time at 120° West, but since Mountain View is at 122.1° West, that means True Noon here occurs 8 minutes later than True Noon at 120° West.  That’s what gnomonists mean when they say 'sundials being local'.

For the nerdiest of nerds, there is still one more wrinkle which we decided to skip. Due to Earth's elliptical orbit and tilted axis, the True Solar Time and Civil Time (that which your watch or smartphone tells you) differ by varying amounts through the year, up to almost 20 minutes. This amount is called “The Equation of Time” (EOT). To get Civil Time you must add the longitude correction (the 8 minutes from not being at 120° West) to True Solar Time plus the Equation of Time value for the day to the Solar Time.

Acknowledgement

The sundial discussion, design and installation were possible due to the active involvement of Willowgate gardeners. We'd like to thank all our fellow Willowgate gardeners who sent in their plant selections. Last but not least, thanks to the City of Mountain View for giving us this opportunity to enhance the community aspect of Willowgate Community Garden.