Work in Progress. Caution: Wet Paint
Look for the date markers along the North-South Line.
Note that half of the calendar is on one side of the line, and the other half is on the other side of the line.
Stand on the white North-South line as close as you can to the current date, facing North (marked “N”).
To help in placement, put your heels’ position on the desired date on the line.
Look to where your shadow falls on the yellow band, between two numbers on the band.
It is one hour between adjacent numbers so if in between, estimate how much past the hour the shadow falls. The number to the left of your shadow plus the fraction of the hour between that number and your shadow is the time. Think of the hour hand on a clock.
What time did you just read? That was “solar time”.
Solar time noon is always with the sun directly south and the highest it will be in the sky for that day. You can’t do anything about solar time. It is what it is, and all you can do is catch what it is right now. This is what Nature and the Universe has given us.
That’s not what my cell phone says.
Look at the date marker closest to where you are standing. There is a number (in minutes) with a + or a – in front of it. Add that to the solar time you just read and you will just about match your cell phone time. This is called the Equation of Time correction. An additional hour would be added for Daylight Savings Time, shown as “+ DST”, for those months currently so afflicted.
The tilt of the Earth on its axis, the ellipticity of the Earth’s orbit around the sun, as well as your position on the Earth cause the apparent time of the sun’s rising, setting, and noon to vary throughout the year, by as much as about 20 minutes.
If you are in between two date markers, you can pick a number in between the two Equation of Time correction numbers and use it to add to your solar time instead. You can read the solar time a little better also if instead of your body’s shadow you use a skinny stick, pointing straight up.
Your cell phone or watch shows “civil time”.
Civil time is just what everybody has agreed to as the time. Go East 100 miles, and it’s still the same time as here, even though the sun might come up 8 minutes earlier. When we switch to Daylight Savings Time, everybody agrees that it is an hour earlier today when the sun comes up than it was yesterday. Why is that OK? Everybody agrees, mostly, because we can synchronize all our group activities better that way.
On the East-West axis of the sundial are two spots marked "Sunset" and "Sunrise". You can click here to go to how to read the time of sunrise or sunset for any day of the year, or to find where the sun will rise or set.
Inside the hour ring are pointers to the locations of historically important observatories of the sun and the heavens around the world. The directions indicated are by great circle navigation. Many of these observatories are thousands of years old and had important roles in the culture and daily lives of the people who built them, or their descendants. Some have deep meaning even today to the inheritors of these structures. The marking of the solstices and equinoxes on this sundial show we live under the same sky as our ancient ancestors. While these people understood the universe in different terms and told different stories, they used minds no different from our own to find their place in it. I encourage you to check out the links below for a bit of the history and background of these treasures.
I've made some small windowsill sundials just for Monta Loma, designed for our latitude and longitude, although they can be used anywhere in the Bay Area and be no more than a few minutes off. You can take a look, and even buy one at a discount by clicking here.
You will notice that living here the Santa Clara Valley, we have mountains around us, and with the houses and trees also around us it is impossible to really see the horizon of a spherical Earth. So this feature of the sundial is really about where and when the sunrise or sunset would be if we could see the horizon. While this doesn’t work so well for us, when you look at the ancient solar and astronomical observatories shown on the sundial face and linked elsewhere on this site, you can easily imagine why locations located on mountains or flat plains were so favored to mark out the position of the sunrise and sunset throughout the year. Marking these solar positions is one way we can share in the experience of anticipating the solstices and equinoxes that were so important to ancient peoples for marking the annual cycles of agricultural, seasonal, and cultural milestones.
For Sunrise position and time:
Look for the date markers along the North-South Line.
Pick any date you like on the North-South line.
Face West and you’ll see half-way to the West marker a spot marked “Sunrise”.
If you trace an imaginary line (or pull a real string) from the date marker through the Sunrise point to the hour ring, the time you read there is the sunrise time for that date.
If you stand on the hour ring and trace that same imaginary line (or pull a real string) from the Sunrise point to the date, the direction the line points to on the horizon in the East is where the sun will rise from on that date.
You can do the same for the “Sunset” point.
Face East from the North-South Line and you’ll see half-way to the East marker a spot marked “Sunset”.
Trace a line from any date on the date marker through the Sunset point to the hour ring for the sunset time for that date.
Trace a line from the Sunset point to any date you like on the date marker and the line’s direction to the horizon will give you the location of sunset for that date.
You may notice that the sunrise’s or sunset’s most extreme positions North or South of due East or West are bounded by the Winter or Summer Solstices on the date marker and are noted with dashed lines radiating from the Sunrise and Sunset points on the sundial. It is difficult to see how the sun changes its position in the sky throughout the year but seeing where it rises and sets is much easier, especially when you can line up the sunrise or sunset with a faraway hilltop or a mark on a sundial. This is the principle of solar alignment most frequently used in the ancient solar observatories to mark the seasons of the year. This has been carried through to today even, with the first day of Winter and Summer on the Solstices, and the start of Spring and Autumn on the Equinoxes.
I don't give more precise information on the location of these sites so that you can explore for yourself their location, what they look like, and their history. But they are found on every inhabited continent and in almost every direction from here.
Kanaloa Stone 250.3°
Majorville Medicine Wheel 24.6°
Big Horn Medicine Wheel 50.7°
Newark Earthworks 72.6°
Watson Brake, LA 92.6°
Poverty Point, LA 91.5°
Wurdi Youang 239.7°
El Caracol, Chichén Itzá 110.5°
Jantar Mantar 342.6°
Rego Grande 99.6°
Zorats Karer 9.3°
Nabta Playa 25.0°
Ahu Akivi 167.6°
Chaco Canyon 92.5°
Tower of the Winds 26.6°